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AVMA (American Veterinary Medical Association) guidelines for the Euthanasia of Animals.

AVMA (American Veterinary Medical Association) guidelines for the Euthanasia of Animals.

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  • 1. AVMA Guidelinesfor the Euthanasiaof Animals: 2013 EditionMembers of the Panel on EuthanasiaSteven Leary, DVM, DACLAM (Chair); Washington University, St. Louis, MissouriWendy Underwood, DVM (Vice Chair); Eli Lilly and Company, Indianapolis, IndianaRaymond Anthony, PhD (Ethicist); University of Alaska Anchorage, Anchorage, AlaskaSamuel Cartner, DVM, MPH, PhD, DACLAM (Lead, Laboratory Animals Working Group); University of Alabama at Birmingham, Birmingham, AlabamaDouglas Corey, DVM (Lead, Equine Working Group); Associated Veterinary Clinic, Walla Walla, WashingtonTemple Grandin, PhD (Lead, Physical Methods Working Group); Colorado State University, Fort Collins, ColoradoCheryl Greenacre, DVM, DABVP (Lead, Avian Working Group); University of Tennessee, Knoxville, TennesseeSharon Gwaltney-Brant, DVM, PhD, DABVT, DABT (Lead, Noninhaled Agents Working Group); ASPCA Poison Control Center, Urbana, IllinoisMary Ann McCrackin, DVM, PhD, DACVS (Lead, Companion Animals Working Group); Virginia Polytechnic Institute and State University, Blacksburg, VirginiaRobert Meyer, DVM, DACVA (Lead, Inhaled Agents Working Group); Mississippi State University, Mississippi State, MississippiDavid Miller, DVM, PhD, DACZM (Lead, Reptiles, Zoo and Wildlife Working Group); Loveland, ColoradoJan Shearer, DVM, MS, DACAW (Lead, Animals Farmed for Food and Fiber Working Group); Iowa State University, Ames, IowaRoy Yanong, VMD (Lead, Aquatics Working Group); University of Florida, Ruskin, FloridaAVMA Staff ConsultantsGail C. Golab, PhD, DVM, MANZCVS, DACAW; Director, Animal Welfare DivisionEmily Patterson-Kane, PhD; Animal Welfare Scientist, Animal Welfare DivisionThe following individuals contributed substantively through their participation in the Panel’s Working Groups and their assistance is sincerelyappreciated.Inhaled Agents—Scott Helms, DVM, DABVP; Lee Niel, PhD; Daniel Weary, PhDNoninhaled Agents—Virginia Fajt, DVM, PhD, DACVCP; Don Sawyer, DVM, PhD, DACVA, DABVPPhysical Methods—Rose Gillesby, DVM; Jeff Hill, PhD; Jennifer Woods, BScAquatics—Craig Harms, DVM, PhD, DACZM; Helen Roberts, DVM; Nick Saint-Erne, DVM; Michael Stoskopf, DVM, PhD, DACZMAvian—Laurel Degernes, DVM, MPH, DABVP; Laurie Hess, DVM, DABVP; Kemba Marshall, DVM, DABVP; James Morrisey, DVM, DABVP; Joanne Paul-Murphy, DVM, DACZM, DACAWCompanion Animals—Kathleen Cooney, MS, DVM; Stacey Frick, DVM; John Mays; Rebecca Rhoades, DVMEquids—Fairfield Bain, DVM, MBA, DACVIM, DACVP, DACVECC; Midge Leitch, VMD, DACVS; Thomas R. Lenz, DVM, MS, DACT; Nathaniel Messer, DVM, DABVP; Hayden Sears, DVM; Stuart Shoemaker, DVM, ACVSFood and Fiber Animals—Eric Benson, PhD; C. Scanlon Daniels, DVM, MBA; John Deen, DVM, PhD, DABVP, DACAW; Robert Evans, PhD, DVM, DACPV; Jerome Geiger, DVM, MS; Dee Griffin, DVM, MS; Christa Goodell, DVM; Glen Johnson, DVM; Richard Reynnells, PhD; James Reynolds, DVM, MVPM, DACAW; Bruce Webster, PhDLaboratory Animals—James Artwhol, MS, DVM, DACLAM; Larry Carbone, DVM, PhD, DACLAM; Paul Flecknell, VetMB, MRCVS, PhD, DECVA, DECLAM, DACLAM, FRCVS; David P. Friedman, PhD; Kathleen Pritchett-Corning, DVM, DACLAM, MRCVSReptiles, Zoo and Wild Animals—Scott Citino, DVM, DACZM; Mark Drew, DVM; Julie Goldstein, DVM; Barry Hartup, DVM, PhD; Gregory Lewbart, MS, VMD, DACZM; Douglas Mader, MS, DVM, DABVP, FRSM; Patrick Morris, DVM, DACZM
  • 2. Copyright © 2013 by the American Veterinary Medical Association 1931 N. Meacham Road Schaumburg, IL 60173The AVMA Guidelines for the Euthanasia of Animals: 2013 Edition (“work”) is licensed under the CreativeCommons Attribution-NonCommercial-NoDerivs 3.0 Unported License (http://creativecommons.org/licenses/by-nc-nd/3.0/). You are free to share, copy, distribute, or transmit the work, provided that proper attribution to theAmerican Veterinary Medical Association is included (but not in any way that suggests that the AVMA endorses youor your use of the work). You may not use this work for commercial purposes, including without limitation any saleof the work, or modify or change the work in any way, or create derivative works from it without permission fromthe American Veterinary Medical Association. ISBN 978-1-882691-21-0
  • 3. CONTENTSPart I—Introduction and General Comments M3. Physical Methods ................................................ 34I1. Preface .................................................................... 5 M3.1 Common Considerations .............................. 34I2. Historical Context and Current Edition ................... 5 M3.2 Penetrating Captive Bolt ............................... 35 I2.1 History of the Panel on Euthanasia ................... 5 M3.3 Nonpenetrating Captive Bolt ........................ 35 I2.2 Substantive Changes Since the Last Edition ...... 5 M3.4 Manually Applied Blunt Force Trauma I2.3 Statement of Use............................................... 6 to the Head .............................................. 36I3. What Is Euthanasia? ................................................ 6 M3.5 Gunshot ....................................................... 36 I3.1 A Good Death as a Matter of Humane Disposition.. 7 M3.5.1 Basic Principles of Firearms................... 36 I3.2 A Good Death as a Matter of Humane M3.5.2 Muzzle Energy Requirements ................ 37 Technique....................................................... 7 M3.5.3 Bullet Selection ..................................... 37I4. Euthanasia and Veterinary Medical Ethics ............... 7 M3.5.4 Firearm Safety ....................................... 37I5. Evaluating Euthanasia Methods ............................. 10 M3.6 Cervical Dislocation ...................................... 38 I5.1 Consciousness and Unconsciousness .............. 11 M3.7 Decapitation ................................................. 38 I5.2 Pain and Its Perception ................................... 12 M3.8 Electrocution ................................................ 39 I5.3 Stress and Distress .......................................... 13 M3.9 Kill Traps ...................................................... 40 I5.4 Animal Behavior ............................................. 13 M3.10 Maceration.................................................. 41 I5.5 Human Behavior............................................. 14 M3.11 Focused Beam Microwave Irradiation ......... 41I6. Mechanisms of Euthanasia .................................... 15 M3.12 Thoracic (Cardiopulmonary, Cardiac)I7. Confirmation of Death .......................................... 16 Compression............................................ 41I8. Disposal of Animal Remains .................................. 16 M3.13 Adjunctive Methods.................................... 41 M3.13.1 Exsanguination ................................... 41Part II—Methods of Euthanasia M3.13.2 Pithing ................................................ 41M1. Inhaled Agents .................................................... 18 M1.1 Common Considerations .............................. 18 Part III—Methods of Euthanasia M1.2 Principles Governing Administration ............ 19 by Species and Environment M1.3 Inhaled Anesthetics ...................................... 20 S1. Companion Animals ............................................. 43 M1.4 Carbon Monoxide......................................... 22 S1.1 General Considerations .................................. 43 M1.5 Nitrogen, Argon ............................................ 23 S1.2 Acceptable Methods ....................................... 43 M1.6 Carbon Dioxide ............................................ 24 S1.2.1 Noninhaled Agents ................................. 43M2. Noninhaled Agents.............................................. 26 S1.3 Acceptable With Conditions Methods ............ 44 M2.1 Common Considerations .............................. 26 S1.3.1 Noninhaled Agents ................................. 44 M2.1.1 Compounding....................................... 27 S1.3.2 Inhaled Agents ....................................... 45 M2.1.2 Residue/Disposal Issues......................... 27 S1.3.3 Physical Methods ................................... 45 M2.2 Routes of Administration .............................. 27 S1.4 Adjunctive Methods ....................................... 46 M2.2.1 Parenteral Injection ............................... 27 S1.5 Unacceptable Methods ................................... 46 M2.2.2 Immersion ............................................ 28 S1.6 Special Considerations ................................... 46 M2.2.3 Topical Application ............................... 28 S1.6.1 Dangerous or Fractious Animals ............. 46 M2.2.4 Oral Administration .............................. 28 S1.6.2 Disposal of Animal Remains ................... 46 M2.3 Barbituric Acid Derivatives ........................... 28 S1.7 Fetuses and Neonates..................................... 46 M2.4 Pentobarbital Combinations ......................... 29 S1.8 Euthanasia in Specific Environments ............. 47 M2.5 Tributame ..................................................... 29 S1.8.1 Individual Animals in Presence of Owners ... 47 M2.6 T-61 .............................................................. 29 S1.8.2 Breeding Facilities .................................. 47M2.7 Ultrapotent Opiods ........................................... 30 S1.8.3 Animal Control, Sheltering, and Rescue M2.8 Dissociative Agents and α2-Adrenergic Facilities ............................................. 47 Receptor Agonists .................................... 30 S1.8.4 Laboratory Animal Facilities ................... 47 M2.9 Potassium Chloride and Magnesium Salts ..... 30 S2. Laboratory Animals .............................................. 48 M2.10 Chloral Hydrate and α Chloralose .............. 31 S2.1 General Considerations .................................. 48 M2.11 Alcohols ..................................................... 31 S2.2 Small Laboratory and Wild-Caught Rodents M2.12 Tricaine Methanesulfonate (MS 222, TMS) . 32 (Mice, Rats, Hamsters, Guinea Pigs, Gerbils, M2.13 Benzocaine Hydrochloride .......................... 32 Degus, Cotton Rats).................................... 48 M2.14 Clove Oil, Isoeugenol, and Eugenol ............ 33 S2.2.1 Acceptable Methods ............................... 48 M2.15 2-Phenoxyethanol....................................... 33 S2.2.2 Acceptable With Conditions Methods .... 48 M2.16 Quinaldine (2-Methylquinoline, S2.2.3 Unacceptable Methods ........................... 49 Quinalidine Sulfate) ................................. 34 S2.2.4 Fetuses and Neonates ............................. 50 M2.17 Metomidate ................................................ 34 S2.3 Laboratory Farm Animals, Dogs, Cats, M2.18 Sodium Hypochlorite ................................. 34 Ferrets, and Nonhuman Primates .............. 50 M2.19 Formaldehyde ............................................ 34 S2.3.1 General Considerations .......................... 50 M2.20 Unacceptable Agents................................... 34 S2.3.2 Special Cases .......................................... 50AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 3
  • 4. CONTENTS S2.4 Laboratory Rabbits ......................................... 50 S6.2 Finfish ................................................................ 69 S2.4.1 General Considerations .......................... 50 S6.2.1 Noninhaled Agents ................................. 69 S2.4.2 Acceptable Methods ............................... 50 S6.2.2 Physical Methods ................................... 70 S2.4.3 Acceptable With Conditions Methods .... 50 S6.2.3 Adjunctive Methods ............................... 71 S2.4.4 Special Cases .......................................... 51 S6.2.4 Unacceptable Methods ........................... 71 S2.5 Laboratory Finfish, Aquatic Invertebrates, S6.2.5 Life Stage Considerations ....................... 71 Amphibians, and Reptiles............................. 51 S6.2.6 Finfish in Particular Environments ......... 72S3. Animals Farmed for Food and Fiber ..................... 51 S6.3 Aquatic Invertebrates ..................................... 74 S3.1 General Considerations .................................. 51 S6.3.1 Acceptable First Steps of 2-Step S3.2 Bovids and Small Ruminants.......................... 51 Methods .............................................. 74 S3.2.1 Cattle ..................................................... 51 S6.3.2 Acceptable Second Steps of 2-Step S3.2.2 Sheep and Goats..................................... 55 Methods.............................................. 74 S3.3 Swine ............................................................. 58 S6.3.3 Life Stage Considerations ....................... 74 S3.3.1 Mature Sows, Boars, and S6.3.4 Unacceptable Methods ........................... 74 Grower-Finisher Pigs .............................58 S7. Captive and Free-Ranging Nondomestic S3.3.2 Nursery Pigs (70 lb or Lighter) ............... 60 Animals ............................................................. 74 S3.3.3 Suckling Pigs .......................................... 61 S7.1 General Considerations .................................. 75 S3.4 Poultry ........................................................... 62 S7.2 Captive Invertebrates ..................................... 75 S3.4.1 Acceptable Methods ............................... 62 S7.2.1 Acceptable Methods ............................... 76 S3.4.2 Acceptable With Conditions Methods .... 62 S7.2.2 Acceptable With Conditions Methods .... 76 S3.4.3 Adjunctive Methods ............................... 63 S7.2.3 Unacceptable Methods ........................... 76 S3.4.4 Embryos and Neonates........................... 63 S7.2.4 Developmental Stages of Invertebrates ... 76S4. Equids .................................................................. 63 S7.3 Captive Amphibians and Reptiles................... 76 S4.1 General Considerations .................................. 63 S7.3.1 Anatomy and Physiology ........................ 76 S4.1.1 Human Safety......................................... 63 S7.3.2 Restraint ................................................. 76 S4.1.2 Disposal of Remains ............................... 64 S7.3.3 Verification of Death ............................... 76 S4.2 Methods......................................................... 64 S7.3.4 Acceptable Methods ............................... 76 S4.2.1 Acceptable Methods ............................... 64 S7.3.5 Acceptable With Conditions Methods .... 77 S4.2.2 Acceptable With Conditions Methods .... 64 S7.3.6 Adjunctive Methods ............................... 78 S4.2.3 Adjunctive Methods ............................... 64 S7.3.7 Unacceptable Methods ........................... 78 S4.2.4 Unacceptable Methods ........................... 64 S7.3.8 Special Cases and Exceptions ................. 78 S4.3 Special Cases and Exceptions ......................... 65 S7.3.9 Destruction of Viable Eggs...................... 78S5. Avians................................................................... 65 S7.4 Captive Nonmarine Mammals........................ 78 S5.1 General Considerations ............................. 65 S7.4.1 General Considerations .......................... 78 S5.1.1 Anatomy and Physiology ........................ 65 S7.4.2 Restraint ................................................. 79 S5.1.2 Restraint ................................................. 65 S7.4.3 Acceptable Methods ............................... 79 S5.2 Methods......................................................... 65 S7.4.4 Acceptable With Conditions Methods .... 79 S5.2.1 Acceptable Methods ............................... 65 S7.4.5 Adjunctive Methods ............................... 80 S5.2.2 Acceptable With Conditions Methods .... 66 S7.4.6 Unacceptable Methods ........................... 80 S5.2.3 Adjunctive Methods ............................... 67 S7.4.7 Embryos, Fetuses, and Neonates ............ 80 S5.2.4 Unacceptable Methods ........................... 67 S7.5 Captive Marine Mammals ............................. 80 S5.3 Eggs, Embryos, and Neonates ........................ 67 S7.5.1 Acceptable Methods ............................... 80S6. Finfish and Aquatic Invertebrates ........................ 67 S7.5.2 Acceptable With Conditions Methods .... 80 S6.1 General Considerations .................................. 67 S7.6 Free-Ranging Wildlife ................................... 81 S6.1.1 Terms Applicable to Ending Life............. 68 S7.6.1 General Considerations .......................... 81 S6.1.2 Human and Animal Considerations........ 68 S7.6.2 Special Considerations ........................... 81 S6.1.3 Preparation and Environment................. 68 S7.6.3 Methods ................................................. 82 S6.1.4 Indicators of Death in Finfish and S7.6.4 Embryos, Fetuses, and Neonates ............ 83 Aquatic Invertebrates ........................... 69 S7.7 Free-Ranging Marine Mammals..................... 83 S6.1.5 Disposition of Euthanized Animals......... 69 S7.7.1 Acceptable Methods ............................... 83 S6.1.6 Finfish and Aquatic Invertebrates S7.7.2 Acceptable With Conditions Methods .... 83 Intended for Human Consumption ...... 69 S7.7.3 Adjunctive Methods ............................... 84 S7.7.4 Unacceptable Methods ........................... 84 References ................................................................ 84 Glossary .................................................................... 984 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 5. Part I—Introduction and General CommentsI1. PREFACE ing and applying appropriate pre-euthanasia (eg, seda- Animal issues are no longer socially invisible. Dur- tion) and animal handling practices, as well as atten-ing the past half-century, efforts to ensure the respect- tion to disposal of animals’ remains.ful and humane treatment of animals have garneredglobal attention.1,2 Concern for the welfare of animals I2. HISTORICAL CONTEXTis reflected in the growth of animal welfare science AND CURRENT EDITIONand ethics. The former is evident in the emergence ofacademic programs, scientific journals, and funding I2.1 HISTORY OF THE PANEL ON EUTHANASIAstreams committed either partially or exclusively to the Since 1963 the AVMA has convened a POE tostudy of how animals are impacted by various environ- evaluate methods and potential methods of euthanasiaments and human interventions. The latter has seen for the purpose of creating guidelines for veterinariansthe application of numerous ethical approaches (eg, who carry out or oversee the euthanasia of animals.rights-based theories, utilitarianism, virtue ethics, con- The scope of the 1963 edition was limited to methodstractarianism, pragmatic ethics) to assessing the moral and recommendations applicable to dogs, cats, andvalue of animals and the nature of the human-animal other small mammals. Subsequent editions publishedrelationship.1,3–9 The proliferation of interest in animal in 1972 and 1978 encompassed more methods and spe-use and care, at the national and international levels, is cies (laboratory animals and food animals, respective-also apparent in recent protections accorded to animals ly), and included additional information about animals’in new and amended laws and regulations, institutional physiologic and behavioral responses to euthanasiaand corporate policies, and purchasing and trade agree- (specifically, pain, stress, and distress), euthanasia’s ef-ments. Changing societal attitudes toward animal care fects on observers, and the economic feasibility and en-and use have inspired scrutiny of some traditional and vironmental impacts of various approaches. In 1986 in-contemporary practices applied in the management of formation on poikilothermic, aquatic, and fur-bearinganimals used for agriculture, research and teaching, wildlife was introduced; in 1993 recommendations forcompanionship, and recreation or entertainment and horses and wildlife were added; and in 2000 an updateof animals encountered in the wild. Attention has also acknowledged a need for more research on approachesbeen focused on conservation and the impact of human suitable for depopulation. An interim revision by theinterventions on terrestrial and aquatic wildlife and the AVMA Animal Welfare Committee in 2007 incorporat-environment. Within these contexts, stakeholders look ed information derived from an existing, but separate,to veterinarians to provide leadership on how to care AVMA policy on the use of maceration to euthanizewell for animals, including how to relieve unnecessary day-old chicks, poults, and pipped eggs, and the namepain and suffering. of the report was changed to the AVMA Guidelines on In creating the 2013 edition of the AVMA Guide- Euthanasia.lines for the Euthanasia of Animals (Guidelines), the The 2013 iteration of the Guidelines constitutesPanel on Euthanasia (POE) made every effort to iden- the eighth edition of the POE’s report. The process fortify and apply the best research and empirical informa- compiling this edition was substantially changed to in-tion available. As new research is conducted and more clude more breadth and depth of expertise in the af-practical experience gained, recommended methods fected species and environments in which euthanasiaof euthanasia may change. As such, the AVMA and its is performed. More than three years of deliberationPOE have made a commitment to ensure the Guide- by more than 60 individuals, including veterinarians,lines reflect an expectation and paradigm of continuous animal scientists, behaviorists, psychologists, and animprovement that is consistent with the obligations of animal ethicist, resulted in the commentary and rec-the Veterinarian’s Oath.10 As for other editions of the ommendations that follow. A comment period alloweddocument, modifications of previous recommendations AVMA members an opportunity to provide input andare also informed by continued professional and public share their experiences directly with POE members.sensitivity to the ethical care of animals. Their input helps ensure the resulting document is not While some euthanasia methods may be utilized in only scientifically robust, but practically sound.slaughter and depopulation, recommendations relatedto humane slaughter and depopulation fall outside the I2.2 SUBSTANTIVE CHANGESpurview of the Guidelines and will be addressed by sep- SINCE THE LAST EDITIONarate documents that are under development. In the 2013 Guidelines, methods, techniques, and The Guidelines set criteria for euthanasia, specify agents of euthanasia have been updated and detailedappropriate euthanasia methods and agents, and are descriptions have been included to assist veterinariansintended to assist veterinarians in their exercise of pro- in applying their professional judgment. Species-spe-fessional judgment. The Guidelines acknowledge that cific sections have been expanded or added to includeeuthanasia is a process involving more than just what more guidance for terrestrial and aquatic species kepthappens to an animal at the time of its death. Apart for a variety of purposes and under different conditions.from delineating appropriate methods and agents, these Information has been incorporated about the handlingGuidelines also recognize the importance of consider- of animals before and during euthanasia, including un-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 5
  • 6. der free-ranging conditions, where the needs of animals sight that may be species specific, available equipmentand the challenges faced by veterinarians and other and facilities, options for disposal, potential secondarypersonnel may be quite different from those in domes- toxicity, and other factors must be considered. Humantic environments. And, where possible, appropriate safety is of utmost importance, and appropriate safetyflowcharts, illustrations, tables, and appendices have equipment, protocols, and knowledge must be availablebeen used to clarify recommendations. Appendices 1 before animals are handled. Advance preparation in-through 3 also may be useful as a quick reference guide, cludes protocols and supplies for addressing personnelbut those performing euthanasia are strongly advised to injury due to animal handling or exposure to drugs andrefer to the full text of the document for important ad- equipment used during the process. Once euthanasiaditional information. Section labels have been included has been carried out, death must be carefully verified.in Appendix 1 to assist readers in locating related text All laws and regulations pertaining to the species beingfor particular species. euthanized, the methods employed, and disposal of the Collection of animals for scientific investigations, animal’s remains and/or water containing any pharma-euthanasia of injured or diseased wildlife, and removal ceuticals used for euthanasia must be followed.of animals causing damage to property or threatening The POE’s objective in creating the Guidelines ishuman safety are addressed. Recognizing that veteri- to provide guidance for veterinarians about how to pre-nary responsibilities associated with euthanasia are not vent and/or relieve the pain and suffering of animalsrestricted to the process itself, additional information that are to be euthanized. While every effort has beenabout confirmation of death and disposal of animal re- made to identify and recommend appropriate approach-mains has been included. es for common species encountered under common One area identified as needing additional guidance conditions, the POE recognized there will be less thanin the last iteration of the Guidelines was depopulation perfect situations in which a recommended method of(ie, the rapid destruction of large numbers of animals euthanasia may not be possible and a method or agentin response to emergencies, such as the control of cata- that is best under the circumstances will need to be ap-strophic infectious diseases or exigent situations caused plied. For this reason, although the Guidelines may beby natural disasters). Depopulation may employ eutha- interpreted and understood by a broad segment of thenasia techniques, but not all depopulation methods general population, a veterinarian should be consultedmeet the criteria for euthanasia. Because they do not al- in their application.ways meet the criteria for euthanasia, these techniqueswill be addressed in a separate document, the AVMA I3. WHAT IS EUTHANASIA?Guidelines for the Depopulation of Animals. Similarly, Euthanasia is derived from the Greek terms eubecause methods used for slaughter or harvest may also meaning good and thanatos meaning death. The term isnot meet all the conditions necessary to be deemed usually used to describe ending the life of an individualeuthanasia, these techniques will be addressed by a animal in a way that minimizes or eliminates pain andthird document, the AVMA Guidelines for the Humane distress. A good death is tantamount to the humane ter-Slaughter of Animals. mination of an animal’s life. In the context of these Guidelines, the veterinar-I2.3 STATEMENT OF USE ian’s prima facie duty in carrying out euthanasia in- The Guidelines are designed for use by members cludes, but is not limited to, (1) his or her humane dis-of the veterinary profession who carry out or oversee position to induce death in a manner that is in accordthe euthanasia of animals. As such, they are intended to with an animal’s interest and/or because it is a matterapply only to nonhuman species. of welfare, and (2) the use of humane techniques to The species addressed by the practice of veterinary induce the most rapid and painless and distress-freemedicine are diverse. A veterinarian experienced with the death possible. These conditions, while separate, arespecies of interest should be consulted when choosing a not mutually exclusive and are codependent.method of euthanasia, particularly when little species-spe- Debate exists about whether euthanasia appropri-cific research on euthanasia has been conducted. Methods ately describes the killing of some animals at the endand agents selected will often be situation specific, as a of biological experiments11 and of unwanted sheltermeans of minimizing potential risks to the animal’s wel- animals. The Panel believes that evaluating the socialfare and personnel safety. Given the complexity of issues acceptability of various uses of animals and/or the ra-that euthanasia presents, references on anatomy, physiol- tionale for inducing death in these cases is beyond itsogy, natural history, husbandry, and other disciplines may purview; however, current AVMA policy supports theassist in understanding how various methods may impact use of animals for various human purposes,12 and alsoan animal during the euthanasia process. recognizes the need to euthanize animals that are un- Veterinarians performing or overseeing euthana- wanted or unfit for adoption.13 Whenever animals aresia must assess the potential for animal distress due to used by humans, good animal care practices should bephysical discomfort, abnormal social settings, novel implemented and adherence to those good practicesphysical surroundings, pheromones or odors from should be enforced. When evaluating our responsibili-nearby or previously euthanized animals, the pres- ties toward animals, it is important to be sensitive to theence of humans, or other factors. In addition, human context and the practical realities of the various types ofsafety and perceptions, availability of trained person- human-animal relationships. Impacts on animals maynel, potential infectious disease concerns, conservation not always be the center of the valuation process, andor other animal population objectives, regulatory over- there is disagreement on how to account for conflicting6 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 7. interspecific interests. The Panel recognizes these are fect to the animal, the humaneness of the technique (ie,complex issues raising concerns across a large number how we bring about the death of animals) is also an im-of domains, including scientific, ethical, economic, en- portant ethical issue. As veterinarians and human be-vironmental, political, and social. ings it is our responsibility to ensure that if an animal’s life is to be taken, it is done with the highest degree ofI3.1 A GOOD DEATH AS A MATTER respect, and with an emphasis on making the death asOF HUMANE DISPOSITION painless and distress free as possible. When euthanasia Humane disposition reflects the veterinarian’s de- is the preferred option, the technique employed shouldsire to do what is best for the animal and serves to bring result in rapid loss of consciousness followed by car-about the best possible outcome for the animal. Thus, diac or respiratory arrest and, ultimately, a loss of braineuthanasia as a matter of humane disposition can be function. In addition, animal handling and the eutha-either intent or outcome based. nasia technique should minimize distress experienced Euthanasia as a matter of humane disposition oc- by the animal prior to loss of consciousness. The POEcurs when death is a welcome event and continued recognized that complete absence of pain and distressexistence is not an attractive option for the animal as cannot always be achieved. The Guidelines attempt toperceived by the owner and veterinarian. When ani- balance the ideal of minimal pain and distress with themals are plagued by disease that produces insurmount- reality of the many environments in which euthanasiaable suffering, it can be argued that continuing to live is performed.is worse for the animal than death or that the animal no While recommendations are made, it is importantlonger has an interest in living. The humane disposi- for those utilizing these recommendations to under-tion is to act for the sake of the animal or its interests, stand that, in some instances, agents and methods ofbecause the animal will not be harmed by the loss of euthanasia identified as appropriate for a particular spe-life. Instead, there is consensus that the animal will be cies may not be available or may become less than anrelieved of an unbearable burden. As an example, when ideal choice due to differences in circumstances. Con-treating a companion animal that is suffering severely versely, when settings are atypical, methods normallyat the end of life due to a debilitating terminal illness, not considered appropriate may become the methoda veterinarian may recommend euthanasia, because the of choice. Under such conditions, the humaneness (orloss of life (and attendant natural decline in physical perceived lack thereof) of the method used to bringand psychological faculties) to the animal is not rela- about the death of an animal may be distinguishedtively worse compared with a continued existence that from the intent or outcome associated with an act ofis filled with prolonged illness, suffering, and duress. killing. Following this reasoning, it may still be an actIn this case, euthanasia does not deprive the animal of of euthanasia to kill an animal in a manner that is notthe opportunity to enjoy more goods of life (ie, to have perfectly humane or that would not be considered ap-more satisfactions fulfilled or enjoy more pleasurable propriate in other contexts. For example, due to lack ofexperiences). And, these opportunities or experiences control over free-ranging wildlife and the stress associ-are much fewer or lesser in intensity than the presence ated with close human contact, use of a firearm mayor intensity of negative states or affect. Death, in this be the most appropriate means of euthanasia. Also,case, may be a welcome event and euthanasia helps to shooting a suffering animal that is in extremis, insteadbring this about, because the animal’s life is not worth of catching and transporting it to a clinic to euthanize itliving but, rather, is worth avoiding. using a method normally considered to be appropriate Veterinarians may also be motivated to bring about (eg, barbiturates), is consistent with one interpretationthe best outcome for the animal. Often, veterinarians of a good death. The former method promotes the ani-face the difficult question of trying to decide (or helping mal’s overall interests by ending its misery quickly, eventhe animal’s owner to decide) when euthanasia would though the latter technique may be considered to bebe a good outcome. In making this decision many vet- more acceptable under normal conditions.18 Neither oferinarians appeal to indices of welfare or quality of life. these examples, however, absolves the individual fromScientists have described welfare as having three com- her or his responsibility to ensure that recommendedponents: that the animal functions well, feels well, and methods and agents of euthanasia are preferentiallyhas the capacity to perform behaviors that are innate or used.species-specific adaptations14–16 (an alternative view isalso available17). An animal has good welfare if, over- I4. EUTHANASIA ANDall, its life has positive value for it. When an animal VETERINARY MEDICAL ETHICSno longer continues to enjoy good welfare (when it no The AVMA has worked to ensure that veterinarianslonger has a life worth living because, on balance, its remain educated about public discourse around animallife no longer has positive value for it, or will shortly be ethics and animal welfare issues and that they are ableovercome by negative states), the humane thing to do is to participate in meaningful ways. While an essentialto give it a good death. Euthanasia relieves the animal’s ingredient in public discourses about animals, soundsuffering, which is the desired outcome. science is by itself inadequate to address questions of ethics and values that surround the appropriate treat-I3.2 A GOOD DEATH AS A MATTER ment of animals, especially as they relate to end-of-lifeOF HUMANE TECHNIQUE issues. To this end, and consistent with its charge, the When the decision has been made to euthanize and POE hopes to provide veterinarians, those under theirthe goal is to minimize pain, distress, and negative ef- supervision, and the public with well-informed andAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 7
  • 8. credible arguments on how to approach the ethically veterinary practice acts, and other guidance emanatingimportant issue of the death of an animal. In so doing, from veterinary professional organizations and regu-it hopes to promote greater understanding regarding latory bodies provide direction for how veterinariansthe contexts or settings involving euthanasia and the should interact with clients and their animals, differentcomplexity of end-of-life issues involving animals. veterinarians may have different personal ethical val- While not a regulatory body, the AVMA also hopes ues1,27 and this may impact their recommendations.to offer guidance to those who may apply these Guide- In their capacity as animal advocate and client ad-lines as part of regulatory structures designed to pro- visor, the precision and credibility of advice providedtect the welfare of animals used for human purposes. By by veterinarians will help to advance client compli-creating and maintaining these Guidelines, the AVMA ance. In many instances when veterinarians are calledhopes to ensure that when a veterinarian or other pro- upon to benefit society through their scientific knowl-fessional intentionally kills an animal under his or her edge, practical experience, and understanding of howcharge, it is done with respect for the interests of the animals are benefited and harmed, straightforward an-animal and that the process is as humane as possible swers may not be forthcoming. In such cases, veterinar-(ie, that it minimizes pain and distress to the animal ians and animal welfare scientists may have to facilitateand that death occurs as rapidly as possible). conscientious decision making by promoting ethical The AVMA does not take the death of nonhuman dialogue.28–31 As advisor and conduit for informationanimals lightly and attempts to provide guidance for its (and while respecting the autonomy of their clients tomembers on both the morality and practical necessity make decisions on behalf of their animals), veterinar-of the intentional killing of animals. Veterinarians, in ians should advance pertinent scientific knowledge andcarrying out the tenets of their Oath, may be compelled ethical concerns related to practices and procedures soto bring about the intentional death of animals for a that their clients and/or society can make informed de-variety of reasons. The finality of death is, in part, what cisions.1makes it an ethically important issue; death forever cuts Veterinarians who are committed to a broad un-off future positive states, benefits, or opportunities.19 In derstanding of the “do no harm” principle may havecases where an animal no longer has a good life, how- to determine whether an animal’s life is worth living,ever, its death also extinguishes permanently any and especially when there is no consensus on when it is ap-all future harms associated with poor welfare or quality propriate to let that life go. While welfare or quality ofof life.18 What constitutes a good life and what counts life is typically adopted as part of the assessment of anas an impoverished life, or one that has limited quality animal’s interests, what is in an animal’s interest needsuch that the death of the animal is the most humane not be singularly identified with its welfare, especially ifoption, are research areas in need of further study by welfare is defined narrowly and if the animal is harmedthe veterinary and ethics communities.20,21 Animal sci- more by its continued life than its death. For example,entists and veterinarians are also investigating the pro- if welfare is defined solely in terms of an animal’s sub-cesses by which an animal dies during the antemortem jective experience, euthanasia may be warranted evenperiod and euthanasia methods and techniques that if the animal is not showing signs of suffering at themitigate harmful effects.22–25 Further research is also present time and if there is some commitment to avoidneeded regarding the different contexts within which harm. Euthanasia may be considered to be the righteuthanasia occurs, so that improvements in the perfor- course to spare the animal from what is to come (inmance and outcomes of euthanasia can be made. conjunction with a more holistic or objective account The intentional killing of healthy animals, as well of what is in an animal’s interest), if medical interven-as those that are impaired, is a serious concern for the tion would only prolong a terminal condition, or if cur-public. When animals must be killed and veterinarians rent health conditions cannot be successfully mitigated.are called upon to assist, the AVMA encourages care- In these instances, intentional killing need not be mo-ful consideration of the decision to euthanize and the tivated by narrow welfare-based interests32 but may bemethod(s) used. This is also true for euthanasia carried connected to the overall value of death to the animal.out during the course of disease control or protection That some animals are subjects-of-a-life,33–36 and thatof public health, as a means of domestic or wild animal human caretakers have moral responsibilities to theirpopulation control, in conjunction with animal use in animals and do not want to see them endure continuedbiomedical research, and in the process of food and fi- harm,37,38 may be factors in deciding whether death is inber production. Killing of healthy animals under such an animal’s interest. (A subject-of-a-life is a being thatcircumstances, while unpleasant and morally challeng- is regarded as having inherent value and should not being, is a practical necessity. The AVMA recognizes such treated as a mere means to an end. It is a being thatactions as acceptable if those carrying out euthanasia possesses an internal existence and has needs, desires,adhere to strict policies, guidelines, and applicable reg- preferences, and a psychosocial identity that extendsulations. through time.3,6) In thinking seriously about veterinary medical eth- In some cases (eg, animals used for research), in-ics, veterinarians should familiarize themselves with tentional killing of the animal to minimize harm tothe plurality of public moral views surrounding ani- it may be trumped by more pressing ends. Here, themal issues and also be cognizant of personal views and decision to kill an animal and how to do so will becomplicating factors that may impact their own ethical complicated by external factors, such as productivity,decision making. While the Veterinarian’s Oath,10 Prin- the greater public and general good, economics, andciples of Veterinary Medical Ethics of the AVMA,26 state concern for other animals. In human-animal relation-8 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 9. ships there usually are other mitigating factors that advocate, should be able to speak frankly about theare relevant besides ones pertaining only to animal animal’s condition and suggest alternatives to eutha-welfare or the animal’s interest(s). In laboratory situ- nasia.ations, for example, where animals are employed as Prima facie, it is the ethical responsibility of vet-research subjects and death may be a terminal point, erinarians to direct animal owners toward euthana-animal welfare considerations are balanced against the sia as a compassionate treatment option when themerits of the experimental design and merits of the re- alternative is prolonged and unrelenting suffering.41search. In such cases, ensuring the respectful and hu- However, accommodating a pluralism of values, in-mane treatment of research animals will be largely up terests, and duties in animal ethics is challenging.to institutional animal care and use committees (IA- This underscores the need for veterinarians to con-CUC). These committees must apply the principles of sider the broader context in thinking about what ani-refinement, replacement, and reduction, and ensure a mal care she or he will prescribe. There are no easyrespectful death for research animals. The decision to reductionist formulas to which to appeal. In manyinduce death may also involve whether replacements cases, advice will need to be responsive to the needscan be created for the animals that are killed.39,40 These at hand. Attention must be given to how the welfareother factors might justify killing an animal, despite and suffering of the animal are understood withinthe fact that the animal might otherwise have had a the context of its whole life and in light of sociallylife worth living. For example, killing may be justified acceptable ways in which humans and animals inter-for disease control or public health purposes, popu- act in different environments.lation control, biomedical research, or slaughter for Because veterinarians are committed to improvingfood and/or fiber. In other instances, keeping an ani- animal and human health and welfare, and becausemal alive that does not have a life worth living can be they work tirelessly to discover causes and cures forjustified (eg, research circumstances where it would animal diseases and promote good animal manage-be impractical to kill the animal or when ensuring its ment, some may feel a sense of disquiet or defeat whensurvival would promote a greater good18). euthanasia becomes the better course of action. The There may be instances in which the decision to POE hopes that these Guidelines and other AVMAkill an animal is questionable, especially if the ani- policies will assist veterinarians who may be strug-mal is predicted to have a life worth living if it is not gling with what may seem to be gratuitous euthana-killed. One example is the healthy companion animal sia, the acceptability of certain procedures, and thewhose owner wants to euthanize it because keeping sometimes routine nature of performing euthanasia.it in the home is no longer possible or convenient. Toward that end, the decision aids in Figures 1 and 2aIn this case, the veterinarian, as advisor and animal are offered as a resource. Figure 1—Veterinarians may appeal to this decision tree as a way to decide whether euthanasia is war- ranted when the proper course of action is not clear.AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 9
  • 10. Figure 2—When attempting to make the best decision possible in a thorough and balanced way, vet- erinarians may find this decision matrix helpful. It can assist in assessing the morality of euthanasia in particular cases, especially if they are less straightforward.I5. EVALUATING EUTHANASIA METHODS the human applying the technique. The Guidelines also In evaluating methods of euthanasia, the POE con- include information about adjunctive methods, whichsidered the following criteria: (1) ability to induce loss are those that should not be used as a sole method ofof consciousness and death with a minimum of pain euthanasia, but that can be used in conjunction withand distress; (2) time required to induce loss of con- other methods to bring about euthanasia.sciousness; (3) reliability; (4) safety of personnel; (5) The POE recognized there will be less-than-perfect situations in which a method of euthanasia that is listedirreversibility; (6) compatibility with intended ani- as acceptable or acceptable with conditions may not bemal use and purpose; (7) documented emotional ef- possible, and a method or agent that is the best underfect on observers or operators; (8) compatibility with the circumstances will need to be applied.subsequent evaluation, examination, or use of tissue; As with many other procedures involving animals,(9) drug availability and human abuse potential; (10) some methods of euthanasia require physical han-compatibility with species, age, and health status; (11) dling of the animal. The amount of control and kindability to maintain equipment in proper working order; of restraint required will be determined by the species,(12) safety for predators or scavengers should the ani- breed, and size of animal involved; the degree of domes-mal’s remains be consumed; (13) legal requirements; tication, tolerance to humans, level of excitement, andand (14) environmental impacts of the method or dis- prior handling experience of the animal; the presenceposition of the animal’s remains. of painful injury or disease; the animal’s social environ- Euthanasia methods are classified in the Guide- ment; and the method of euthanasia and competence oflines as acceptable, acceptable with conditions, and the person(s) performing the euthanasia. Proper han-unacceptable. Acceptable methods are those that con- dling is vital to minimize pain and distress in animals,sistently produce a humane death when used as the sole to ensure the safety of the person performing eutha-means of euthanasia. Methods acceptable with condi- nasia, and, often, to protect other people and animals.tions are those techniques that may require certain Handling animals that are not accustomed to humansconditions to be met to consistently produce humane or that are severely injured or otherwise compromiseddeath, may have greater potential for operator error or may not be possible without inducing stress, so somesafety hazard, are not well documented in the scientific latitude in the means of euthanasia is needed in someliterature, or may require a secondary method to ensure situations. The POE discussed the criteria for euthana-death. Methods acceptable with conditions are equiva- sia used in the Guidelines as they apply to circumstanc-lent to acceptable methods when all criteria for applica- es when the degree of control over the animal makes ittion of a method can be met. Unacceptable techniques difficult to ensure death without pain and distress. Pre-are those methods deemed inhumane under any condi- medication with the intent of providing anxiolysis, an-tions or that the POE found posed a substantial risk to algesia, somnolence for easier and safer IV access, and10 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 11. reduction of stage II or postmortem activity that could diseases of concern to population health is suspected.be distressing to personnel is strongly encouraged to re- Appropriate diagnostic samples should be collectedduce animal distress and improve personnel safety. This for testing, pertinent regulatory authorities should beis particularly important for prey species, nondomesti- notified, and the animal’s body should be incinerated,cated species, and animals enduring painful conditions. if possible. Use of personal protective equipment and Personnel who perform euthanasia must dem- precautions for handling biohazardous materials areonstrate proficiency in the use of the technique in a recommended. Animals that have injured humans mayclosely supervised environment. Each facility or insti- require specific actions to be taken depending on localtution where euthanasia is performed (whether a clinic, and state laws.laboratory, or other setting) is responsible for trainingits personnel adequately to ensure the facility or insti- I5.1 CONSCIOUSNESStution operates in compliance with federal, state, and AND UNCONSCIOUSNESSlocal laws. Furthermore, experience in the humane Unconsciousness, defined as loss of individualrestraint of the species of animal to be euthanized is awareness, occurs when the brain’s ability to integrateimportant and should be expected, to ensure that ani- information is blocked or disrupted. In humans, on-mal pain and distress are minimized. Training and ex- set of anesthetic-induced unconsciousness has beenperience should include familiarity with the normal functionally defined by loss of appropriate responsebehavior of the species being euthanized, an apprecia- to verbal command; in animals, by loss of the rightingtion of how handling and restraint affect that behavior, reflex.42,43 This definition, introduced with the discov-and an understanding of the mechanism by which the ery of general anesthesia more than 160 years ago, isselected technique induces loss of consciousness and still useful because it is an easily observable, integrateddeath. Euthanasia should only be attempted when the whole-animal response.necessary drugs and supplies are available to ensure a Anesthetics produce unconsciousness either bysmooth procedure. preventing integration (blocking interactions among Selection of the most appropriate method of eutha- specialized brain regions) or by reducing informationnasia in any given situation depends on the species and (shrinking the number of activity patterns availablenumber of animals involved, available means of animal to cortical networks) received by the cerebral cortexrestraint, skill of personnel, and other considerations. or equivalent structure(s). Further, the abrupt loss ofInformation in the scientific literature and available consciousness that occurs at a critical concentrationfrom practical experience focuses primarily on domes- of anesthetic implies that the integrated repertoire ofticated animals, but the same general considerations neural states underlying consciousness may collapseshould be applied to all species. nonlinearly.44 Cross-species data suggest that memory Euthanasia must be performed in accord with ap- and awareness are abolished with less than half theplicable federal, state, and local laws governing drug concentration required to abolish movement. Thus, anacquisition, use, and storage, occupational safety, and anesthetic state (unconsciousness and amnesia) can bemethods used for euthanasia and disposal of animals, produced at concentrations of anesthetic that do notwith special attention to species requirements where prevent physical movements.43possible. The AVMA encourages those responsible for Measurements of brain electrical function haveperforming euthanasia of nonhuman animals to review been used to objectively quantify the unconscious state.current federal, state, and local regulations. If drugs At some level between behavioral unresponsivenesshave been used, careful consideration must be given to and the induction of a flat electroenencephalogramappropriate disposal of the animal’s remains and steps (EEG; indicating the cessation of the brain’s electricalshould be taken to avoid environmental contamination activity and brain death), consciousness must vanish.and human and animal exposures to residues. However, EEG data cannot provide definitive answers Circumstances may arise that are not clearly cov- as to onset of unconsciousness. Brain function moni-ered by the Guidelines. Whenever such situations arise, tors based on EEG are limited in their ability to directlya veterinarian experienced with the species should ap- indicate presence or absence of unconsciousness, espe-ply professional judgment, knowledge of clinically ac- cially around the transition point44; also, it is not alwaysceptable techniques, professional ethos, and social con- clear which EEG patterns are indicators of activation byscience in selecting an appropriate technique for end- stress or pain.25ing an animal’s life. Physical methods that destroy or render nonfunc- It is imperative that death be verified after euthana- tional the brain regions responsible for cortical integra-sia and before disposal of the animal. An animal in deep tion (eg, gunshot, captive bolt, cerebral electrocution,narcosis following administration of an injectable or in- blunt force trauma, maceration) produce instantaneoushalant agent may appear to be dead, but might even- unconsciousness. When physical methods directlytually recover. Death must be confirmed by examining destroy the brain, signs of unconsciousness includethe animal for cessation of vital signs. Consideration immediate collapse and a several-second period of te-should be given to the animal species and method of tanic spasm, followed by slow hind limb movementseuthanasia when determining appropriate criteria for of increasing frequency45–47 in cattle; however, there isconfirming death. species variability in this response. The corneal reflex Safe handling and disposal of the resulting animal will be absent.48 Signs of effective electrocution are lossremains are also critically important when the presence of righting reflex, loss of eyeblink and moving objectof zoonotic disease, foreign animal diseases, or other tracking, extension of the limbs, opisthotonos, down-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 11
  • 12. ward rotation of the eyeballs, and tonic spasm changing transaction that blocks the ascending nociceptive path-to clonic spasm, with eventual muscle flaccidity.49,50 ways. In contrast, administration of a local anesthetic Decapitation and cervical dislocation as physical into the epidural space suppresses both spinally me-methods of euthanasia require separate comment. The diated nociceptive reflexes and ascending nociceptiveinterpretation of brain electrical activity, which can per- pathways; in either case, noxious stimuli are not per-sist for up to 30 seconds following these methods,51–54 ceived as pain in conscious human or nonhuman ani-has been controversial.55 As indicated previously, EEG mals because activity in the ascending pathways, andmethods cannot provide definitive answers as to onset thus access to the higher cortical centers, is suppressedof unconsciousness. Other studies56–59 indicate such ac- or blocked. It is therefore incorrect to substitute thetivity does not imply the ability to perceive pain and term pain for stimuli, receptors, reflexes, or pathwaysconclude that loss of consciousness develops rapidly. because the term implies higher sensory processing as- Once loss of consciousness occurs, subsequently sociated with conscious perception. Consequently, theobserved activities, such as convulsions, vocalization, choice of a euthanasia agent or method is less criticalreflex struggling, breath holding, and tachypnea, can be if it is to be used on an animal that is anesthetized orattributed to the second stage of anesthesia, which by unconscious, provided that the animal does not regaindefinition lasts from loss of consciousness to the on- consciousness prior to death.set of a regular breathing pattern.60,61 Thus, events ob- Pain is subjective in the sense that individuals canserved following loss of the righting reflex are likely not differ in their perceptions of pain intensity as well asconsciously perceived. Some agents may induce con- in their physical and behavioral responses to it. Painvulsions, but these generally follow loss of conscious- can be broadly categorized as sensory-discriminative,ness. Agents inducing convulsions prior to loss of con- where the origin and the stimulus causing pain aresciousness are unacceptable for euthanasia. determined, or as motivational-affective, where the se- verity of the stimulus is perceived and a response toI5.2 PAIN AND ITS PERCEPTION it determined.63 Sensory-discriminative nociceptive Criteria for painless death can be established only processing occurs within cortical and subcortical struc-after the mechanisms of pain are understood. The per- tures using mechanisms similar to those used to processception of pain is defined as a conscious experience.43 other sensory-discriminatory input and provides infor-The International Association for the Study of Pain mation on stimulus intensity, duration, location, and(IASP) describes pain as “An unpleasant sensory and quality. Motivational-affective processing involves theemotional experience associated with actual or poten- ascending reticular formation for behavioral and corti-tial tissue damage, or described in terms of such dam- cal arousal, as well as thalamic input to the forebrainage. Activity induced in the nociceptor and nociceptive and limbic system for perception of discomfort, fear,pathways by a noxious stimulus is not pain, which is anxiety, and depression. Motivational-affective neuralalways a psychological state, even though we may well networks also provide strong inputs to the limbic sys-appreciate that pain most often has a proximate physi- tem, hypothalamus, and autonomic nervous system forcal cause.”62 reflex activation of the cardiovascular, pulmonary, and The perception of pain based on mammalian mod- pituitary-adrenal systems.els requires nerve impulses from peripheral nociceptors Although the perception of pain requires a con-to reach a functioning conscious cerebral cortex and scious experience, defining consciousness, and there-the associated subcortical brain structures. Noxious fore the ability to perceive pain, across many speciesstimulation that threatens to damage or destroy tis- is quite difficult. Previously it was thought that finfish,sue produces activity in primary nociceptors and other amphibians, reptiles, and invertebrates lacked the ana-sensory nerve endings. In addition to mechanical and tomic structures necessary to perceive pain as we un-thermal stimulation, a variety of endogenous substanc- derstand it in birds and mammals. For example, the in-es can generate nociceptive impulses, including pros- vertebrate taxa include animals with no nervous systemtaglandins, hydrogen ions, potassium ions, substance (eg, sponges) and nervous systems with no ganglion-P, purines, histamine, bradykinin, and leukotrienes, as ation or minimal ganglionation (eg, starfish). However,can electrical currents. there are also invertebrate taxa with well-developed Nociceptive impulses are conducted by nociceptor brains and/or complex behaviors that include the abil-primary afferent fibers to either the spinal cord or the ity to analyze and respond to complex environmentalbrainstem and two general sets of neural networks. Re- cues (eg, octopus, cuttlefish, spiders,64,65 honeybees,flex withdrawal and flexion in response to nociceptive butterflies, ants). Most invertebrates do respond toinput are mediated at the spinal level while ascending noxious stimuli and many have endogenous opioids.66nociceptive pathways carry impulses to the reticular Amphibians and reptiles also represent taxa withformation, hypothalamus, thalamus, and cerebral cor- a diverse range of anatomic and physiologic character-tex (somatosensory cortex and limbic system) for sen- istics such that it is often difficult to ascertain that ansory processing and spatial localization. Thus, move- amphibian or reptile is, in fact, dead. Although amphib-ment observed in response to nociception can be due to ians and reptiles respond to noxious stimuli and arespinally mediated reflex activity, cerebral cortical and presumed to feel pain, our understanding of their no-subcortical processing, or a combination of the two. ciception and response to stimuli is incomplete. Never-For example, it is well recognized clinically that spi- theless, there is increasing taxa-specific evidence of thenally mediated nociceptive reflexes may remain intact efficacy of analgesics to minimize the impact of noxiousdistal to a compressive spinal lesion or complete spinal stimuli on these species.67,68 Consequently, euthanasia12 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 13. techniques that result in “rapid loss of consciousness” comfort.79 To avoid distress, veterinarians should striveand “minimize pain and distress” should be strived for, to euthanize animals within the animals’ physical andeven where it is difficult to determine that these criteria behavioral comfort zones (eg, preferred temperatures,have been met. natural habitat, home) and, when possible, prepare a Compelling recent evidence indicates finfish possess calming environment.the components of nociceptive processing systems simi-lar to those found in terrestrial vertebrates,55–70 though I5.4 ANIMAL BEHAVIORdebate continues based on questions of the impact of The need to minimize animal distress, includingquantitative differences in numbers of specific compo- negative affective or experientially based states like fear,nents such as unmyelinated C fibers in major nerve bun- aversion, anxiety, and apprehension, must be consid-dles. Suggestions that finfish responses to pain merely ered in determining the method of euthanasia. Etholo-represent simple reflexes71 have been refuted by stud- gists and animal welfare scientists are getting better aties72,73 demonstrating forebrain and midbrain electrical discerning the nature and content of these states. Vet-activity in response to stimulation and differing with erinarians and other personnel involved in performingtype of nociceptor stimulation. Learning and memory euthanasia should familiarize themselves with pre-eu-consolidation in trials where finfish are taught to avoid thanasia protocols and be attentive to species and indi-noxious stimuli have moved the issue of finfish cogni- vidual variability. For virtually all animals, being placedtion and sentience forward74 to the point where the pre- in a novel environment is stressful80–83; therefore, a eu-ponderance of accumulated evidence supports the posi- thanasia approach that can be applied in familiar sur-tion that finfish should be accorded the same consider- roundings may help reduce stress.ations as terrestrial vertebrates in regard to relief from For animals accustomed to human contact, gentlepain. The POE was not able to identify similar studies of restraint (preferably in a familiar and safe environ-Chondrichthyes (cartilaginous finfish), amphibians, rep- ment), careful handling, and talking during euthanasiatiles, and invertebrates, but believes that available infor- often have a calming effect and may also be effectivemation suggests that efforts to relieve pain and distress coping strategies for personnel.84 Sedation and/or an-for these taxa are warranted, unless further investigation esthesia may assist in achieving the best conditions fordisproves a capacity to feel pain or distress. euthanasia. It must be recognized that sedatives or an- While there is ongoing debate about finfishes’, am- esthetics given at this stage that change circulation mayphibians’, reptiles’, and invertebrate animals’ ability to delay the onset of the euthanasia agent.feel pain or otherwise experience compromised wel- Animals that are in social groups of conspecifics orfare, they do respond to noxious stimuli. Consequently, that are wild, feral, injured, or already distressed fromthe Guidelines assume that a conservative and humane disease pose another challenge. For example, mammalsapproach to the care of any creature is warranted, jus- and birds that are not used to being handled have highertifiable, and expected by society. Euthanasia methods corticosteroid levels during handling and restraint com-should be employed that minimize the potential for pared with animals accustomed to frequent handling bydistress or pain in all animal taxa, and these methods people.85–87 For example, beef cattle that are extensivelyshould be modified as new taxa-specific knowledge of raised on pasture or range have higher corticosteroid lev-their physiology and anatomy is acquired. els when restrained in a squeeze chute compared with intensively raised dairy cattle that are always in close as-I5.3 STRESS AND DISTRESS sociation with people,88,89 and being placed in a new cage An understanding of the continuum that represents has been shown to be stressful for rodents.90 Becausestress and distress is essential for evaluating techniques handling may be a stressor for animals less accustomedthat minimize any distress experienced by an animal be- to human contact (eg, wildlife, feral species, zoo animals,ing euthanized. Stress has been defined as the effect of and some laboratory animals), the methods of handlingphysical, physiologic, or emotional factors (stressors) and degree of restraint (including none, such as for gun-that induce an alteration in an animal’s homeostasis shot) required to perform euthanasia should be consid-or adaptive state.75 The response of an animal to stress ered when evaluating various methods.76 When handlingrepresents the adaptive process that is necessary to re- such animals, calming may be accomplished by retain-store the baseline mental and physiologic state. These ing them (as much as possible) in familiar environments,responses may involve changes in an animal’s neuro- and by minimizing visual, auditory, and tactile stimula-endocrinologic system, autonomic nervous system, tion. When struggling during capture or restraint mayand mental status that may result in overt behavioral cause pain, injury, or anxiety to the animal or danger tochanges. An animal’s response varies according to its the operator, the use of tranquilizers, analgesics, and/orexperience, age, species, breed, and current physiologic anesthetics may be necessary. A method of administra-and psychological state, as well as handling, social en- tion should be chosen that causes the least distress in thevironment, and other factors.76,77 animal for which euthanasia must be performed. Various Stress and the resulting responses have been divid- techniques for oral delivery of sedatives to dogs and catsed into three phases.78 Eustress results when harmless have been described that may be useful under these cir-stimuli initiate adaptive responses that are beneficial to cumstances.91,92the animal. Neutral stress results when the animal’s re- Expressions and body postures that indicate vari-sponse to stimuli causes neither harmful nor beneficial ous emotional states of animals have been described foreffects to the animal. Distress results when an animal’s some species.93–96 Behavioral responses to noxious stim-response to stimuli interferes with its well-being and uli in conscious animals include distress vocalization,AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 13
  • 14. struggling, attempts to escape, and defensive or redi- aware of the potential for substantive psychological im-rected aggression. In cattle and pigs, vocalization dur- pacts of animal euthanasia on people.ing handling or painful procedures is associated with The first setting is the veterinary clinical settingphysiologic indicators of stress.97–99 Vocalization is asso- (clinics and hospitals or mobile veterinary practices)ciated with excessive pressure applied by a restraint de- where owners have to make decisions about whethervice.100,101 Salivation, urination, defecation, evacuation and when to euthanize. Although many owners relyof anal sacs, pupillary dilatation, tachycardia, sweating, heavily on their veterinarian’s judgment, others mayand reflex skeletal muscle contractions causing shiver- have misgivings about making a decision. This is par-ing, tremors, or other muscular spasms may occur in ticularly likely if an owner feels responsible for an ani-unconscious as well as conscious animals. Fear can mal’s medical or behavioral problem. Owners choosecause immobility or playing dead in certain species, euthanasia for their animals for a variety of reasons,particularly rabbits and chickens.102 This immobility including prevention of suffering from a terminal ill-response should not be interpreted as loss of conscious- ness, their inability to care for the animal, the impact ofness when the animal is, in fact, conscious. Distress vo- the animal’s condition on other animals or people, and/calizations, fearful behavior, and release of certain odors or financial considerations. The decision to euthanizeor pheromones by a frightened animal may cause anxi- often carries strong feelings of emotion such as guilt,ety and apprehension in other animals.103,104 Therefore, sadness, shock, and disbelief.115 As society continues tofor sensitive species, it is desirable that other animals pay more attention to questions about the moral statusnot be present when individual animal euthanasia is of animals, loss of animal life should be handled withperformed. Often, simple environmental modifications the utmost respect and compassion by all animal carecan help reduce agitation and stress, such as providing staff. The ability to communicate well is crucial to help-a nonslip floor for the animals to stand on, reducing ing owners make end-of-life decisions for their animalsnoise, blocking the animal’s vision with a blindfold or a and is a learned skill that requires training.116barrier, or removing distracting stimuli that cause ani- Almost 80% of clients who recently experienced themals to become agitated.101,105–108 death of a pet (87% by euthanasia) reported a positive correlation between support from the veterinarian andI5.5 HUMAN BEHAVIOR staff and their ability to handle the grief associated with The depth of the emotional attachment between their pet’s death.115 Owners should be given the oppor-animals and their owners or caretakers requires an ad- tunity to be present during euthanasia, when feasible,ditional layer of professional respect and care beyond and they should be prepared for what to expect.110,115,117the ethical obligation to provide a good death for the What drugs are being used and how the animal couldanimal. Human concerns associated with the euthana- respond should be discussed. Behaviors such as vocal-sia of healthy and unwanted animals can be particularly ization, agonal breaths, muscle twitches, failure of thechallenging, as can situations where the health inter- eyelids to close, urination, or defecation can be dis-ests of groups of animals and/or the health interests of tressing to owners. Counseling services for owners hav-people conflict with the welfare of individual animals ing difficulty coping with animal death are available in(eg, animal health emergencies). some communities, and veterinarians are encouraged The human-animal relationship should be re- to seek grief support training to assist their clients.118–120spected by discussing euthanasia openly, providing an While good euthanasia practices (ie, client communica-appropriate place to conduct the process, offering the tion and education, compassionate species-appropriateopportunity for animal owners and/or caretakers to be handling and selection of technique, pre-euthanasiapresent when at all possible (consistent with the best sedatives or anesthetics as needed to minimize anxietyinterests of the animal and the owners and caretakers), and facilitate safe restraint, and careful confirmation offully informing those present about what they will see death) are often applied in the euthanasia of dogs and(including possible unpleasant side effects), and giving cats, they should also be followed for other species thatemotional support and information about grief coun- are kept as pets, including small mammals, birds, rep-seling as needed.109–111 Regardless of the euthanasia tiles, farm animals, and aquatic animals.method chosen, it is important to consider the level The second setting is in animal care and controlof understanding and perceptions of those in atten- facilities where unwanted, homeless, diseased, and in-dance as they witness euthanasia. When death has been jured animals must be euthanized in large numbers.achieved and verified, owners and caretakers should be The person performing euthanasia must be techni-verbally notified.110 cally proficient (including the use of humane handling Owners and caretakers are not the only people methods and familiarity with the method of euthanasiaaffected by the euthanasia of animals. Veterinarians being employed), and must be able to understand andand their staffs may also become attached to patients communicate to others the reasons for euthanasia andand struggle with the ethics of the caring-killing para- why a particular approach was selected. This requiresdox,112,113 particularly when they must end the lives of organizational commitment to provide ongoing profes-animals they have known and treated for many years. sional training on the latest methods, techniques, andRepeating this scenario regularly may lead to emotional materials available for euthanasia.burnout, or compassion fatigue. The various ways in Distress may develop among personnel directly in-which veterinarians cope with euthanasia have been volved in performing euthanasia repeatedly,121 and maydiscussed elsewhere.114 include a psychological state characterized by a strong There are six settings in which the Panel was most sense of work dissatisfaction or alienation, which may14 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 15. be expressed by absenteeism, belligerence, or careless tion to public perceptions, however, should not out-and callous handling of animals.122 The impact on per- weigh the primary responsibility of doing what is in thesonnel may be worse when euthanasia is conducted in animal’s best interest under the circumstances (ie, usingfrequent, shorter sessions compared with fewer, longer the most appropriate and painless euthanasia methodsessions.123 In addition, animal shelter personnel have possible).been shown to have more difficulty dealing emotion- In addition to ensuring good care of animals dur-ally with the euthanasia of healthy, unwanted animals ing euthanasia and considering the psychological well-than those that are old, sick, injured, or wild.124 Specific being of human participants, the physical safety of per-coping strategies that can make the task more tolerable sonnel handling the animals and performing euthanasiainclude adequate training programs so that euthana- needs to be protected. The safe use of controlled sub-sia is performed competently, rotation of duties and stances and diversion control to prevent abuse is alsoshared responsibilities for staff performing euthanasia, part of the responsibility of those using such substancespeer support in the workplace, professional support as in the performance of euthanasia.131necessary, focusing on animals that are successfully ad-opted or returned to owners, devoting some work time I6. MECHANISMS OF EUTHANASIAto educational activities, and providing time off when Euthanizing agents cause death by three basicworkers feel distressed. Management should be aware mechanisms: (1) direct depression of neurons neces-of potential personnel problems related to animal eu- sary for life function, (2) hypoxia, and (3) physical dis-thanasia and determine whether it is necessary to in- ruption of brain activity. The euthanasia process shouldstitute a program to prevent, decrease, or eliminate this minimize or eliminate pain, anxiety, and distress priorproblem. to loss of consciousness. As loss of consciousness re- The third setting is the laboratory. Researchers, sulting from these mechanisms can occur at differenttechnicians, and students may become attached to ani- rates, the suitability of a particular agent or methodmals that must be euthanized in laboratory settings, will depend on whether an animal experiences distresseven though the animals are often purpose-bred for re- prior to loss of consciousness.search.125 The human–research animal bond positively Unconsciousness, defined as loss of individualimpacts quality of life for a variety of research animals, awareness, occurs when the brain’s ability to integratebut those caring for the animals often experience eu- information is blocked or disrupted (see commentsthanasia-related stress symptoms comparable to those on unconsciousness for additional information). Ide-encountered in veterinary clinics and animal shel- ally, euthanasia methods should result in rapid loss ofters.126–128 The same considerations afforded pet owners consciousness, followed by cardiac or respiratory arrestor shelter employees should be provided to those work- and the subsequent loss of brain function. Loss of con-ing in laboratories, particularly the provision of train- sciousness should precede loss of muscle movement.ing to promote grief coping skills.129 Agents and methods that prevent movement through The fourth setting is wildlife conservation and muscle paralysis, but that do not block or disrupt themanagement. Wildlife biologists, wildlife managers, cerebral cortex or equivalent structures (eg, succinyl-and wildlife health professionals are often responsible choline, strychnine, curare, nicotine, potassium, orfor euthanizing animals that are injured, diseased, or magnesium salts), are not acceptable as sole agents forin excessive number or those that threaten property euthanasia of vertebrates because they result in distressor human safety. Although relocation of some animals and conscious perception of pain prior to death. In con-may be appropriate and attempted, relocation is often trast, magnesium salts are acceptable as the sole agentonly a temporary solution and may be insufficient to for euthanasia in many invertebrates due to the absenceaddress a larger problem. People who must deal with of evidence for cerebral activity in some members ofthese animals, especially under public pressure to save these taxa,132,133 and there is evidence that the magne-the animals rather than destroy them, can experience sium ion acts centrally in suppressing neural activity ofextreme distress and anxiety. In addition, the percep- cephalopods.134tions of not only the wildlife professionals, but of on- Depression of the cortical neural system causes losslookers, need to be considered when selecting a eutha- of consciousness followed by death. Depending on thenasia method. speed of onset of the particular agent or method used, The fifth setting is livestock and poultry produc- release of inhibition of motor activity may be observedtion. As for shelter and laboratory animal workers, on- accompanied by vocalization and muscle contractionfarm euthanasia of individual animals by farm workers similar to that seen in the initial stages of anesthesia.charged with nurturing and raising production animals Although distressing to observers, these responses docan take a heavy toll on employees both physically and not appear to be purposeful. Once ataxia and loss ofemotionally.130 righting reflex occurs, subsequent observed motor The sixth setting is that in which there is broad activity, such as convulsions, vocalization, and reflexpublic exposure. Because euthanasia of zoo animals, struggling, can be attributed to the second stage ofanimals involved in roadside or racetrack accidents, anesthesia, which by definition lasts from the loss ofstranded marine animals, and nuisance or injured wild- consciousness to the onset of a regular breathing pat-life can draw public attention, human attitudes and tern.60,61responses must be considered whenever these animals Hypoxia is commonly achieved by exposing ani-are euthanized. Natural disasters and foreign animal mals to high concentrations of gases that displace oxy-disease programs also present public challenges. Atten- gen (O2), such as carbon dioxide (CO2), nitrogen (N2),AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 15
  • 16. or argon (Ar), or by exposure to carbon monoxide I8. DISPOSAL OF ANIMAL REMAINS(CO) to block uptake of O2 by red blood cells. Exsan- Regardless of the euthanasia method chosen, ani-guination, an adjunctive method, is another method of mal remains must be handled appropriately and in ac-inducing hypoxia, albeit indirectly, and can be a way to cord with state and local law. Regulations apply not onlyensure death in an already unconscious or moribund to the disposition of the animal’s remains (eg, burial,animal. As with other euthanasia methods, some ani- incineration, rendering), but also to the managementmals may exhibit motor activity or convulsions follow- of chemical residues (eg, pharmaceuticals [includinging loss of consciousness due to hypoxia; however, this but not limited to barbiturates, such as pentobarbital]is reflex activity and is not consciously perceived by the and other residues, such as lead) that may adversely af-animal. In addition, methods based on hypoxia will not fect scavengers or result in the adulteration of renderedbe appropriate for species that are tolerant of prolonged products used for animal feed.periods of hypoxemia. Use of pentobarbital invokes legal responsibilities Physical disruption of brain activity can be pro- for veterinarians, animal shelters, and animal ownersduced through a blow to the skull resulting in concus- to properly dispose of animal remains after death. Ani-sive stunning; through direct destruction of the brain mal remains containing pentobarbital are potentiallywith a captive bolt, bullet, or pithing rod; or through poisonous for scavenging wildlife, including birds (eg,depolarization of brain neurons following electrocu- bald and golden eagles, vultures, hawk species, gulls,tion. Death quickly follows when the midbrain centers crows, ravens), carnivorous mammals (eg, bears, mar-controlling respiration and cardiac activity fail. Convul- tens, fishers, foxes, lynxes, bobcats, cougars), andsions and exaggerated muscle activity can follow loss of domestic dogs.137 Federal laws protecting many ofconsciousness. Physical disruption methods are often these species apply to secondary poisoning from ani-followed by exsanguination. These methods are inex- mal remains containing pentobarbital. The Migratorypensive, humane, and painless if performed properly, Bird Treaty Act, the Endangered Species Act, and theand leave no drug residues in the animal’s remains . Bald and Golden Eagle Protection Act may carry civilFurthermore, animals presumably experience less fear and criminal penalties, with fines in civil cases up toand anxiety with methods that require little preparatory $25,000 and in criminal cases up to $500,000 and in-handling. However, physical methods usually require a carceration for up to 2 years.137 Serious repercussionsmore direct association of the operator with the animals may occur when veterinary health professionals whoto be euthanized, which can be offensive to, and upset- should be well-informed about the necessity for properting for, the operator. Physical methods must be skill- disposal of animal remains fail to provide it, or fail tofully executed to ensure a quick and humane death, inform their clients how to provide it, whether therebecause failure to do so can cause substantial suffering. was intent to cause harm or not.138,139 Cases of suspect- In summary, the cerebral cortex or equivalent ed wildlife death from animal remains containing pen-structure(s) and associated subcortical structures must tobarbital are investigated by the regional US Fish andbe functional for pain to be perceived. If the cerebral Wildlife Service law enforcement office.cortex is nonfunctional because of neuronal depres- Recommendations by the US Fish and Wildlife Ser-sion, hypoxia, or physical disruption, pain is not expe- vice for prevention of secondary poisoning from pen-rienced. Reflex motor activity that may occur following tobarbital are to (1) incinerate or cremate animal re-loss of consciousness, although distressing to observers, mains whenever possible, (2) immediately bury deeplyis not perceived by the animal as pain or distress. Giv- according to local laws and regulations, (3) securelyen that we are limited to applying euthanasia methods cover or store animal remains if the ground is frozenbased on these three basic mechanisms, efforts should until such time as deep burial is practical, (4) reviewbe directed toward educating individuals involved in and modify local landfill practices to prevent access ofthe euthanasia process, achieving technical proficiency, scavengers to legally disposed animal remains, (5) edu-and refining the application of existing methods.135 cate clients about proper disposal, (6) include a warn- ing regarding disposal of animal remains on the eutha-I7. CONFIRMATION OF DEATH nasia consent form, and (7) tag animal remains and Death must be confirmed before disposal of any an- outer bags or containers with prominent poison tags.137imal remains. A combination of criteria is most reliable Rendering is an important means of disposal ofin confirming death, including lack of pulse, breathing, dead livestock and horses, and since many horses arecorneal reflex and response to firm toe pinch, inabil- euthanized with barbiturates, related residues can beity to hear respiratory sounds and heartbeat by use of hazardous. Rendered protein is used in animal feed fora stethoscope, graying of the mucous membranes, and cattle, swine, poultry, finfish, aquatic invertebrates, andrigor mortis. None of these signs alone, except rigor companion animals, but products rendered from rumi-mortis, confirms death. nants are prohibited by law for use in ruminant feed. In small animals, particularly in animal shelter set- Many pet food manufacturers have lowered their accep-tings, verification of death may be supplemented by tance thresholds for barbiturate concentrations in ren-percutaneous cardiac puncture after the animal is un- dered product. Advances in analytical chemistry haveconscious. Failure of the needle and attached syringe to spawned increasingly sensitive assays, and pet foodmove after insertion into the heart (aspiration of blood manufacturers are using these techniques to ensureprovides evidence of correct location) indicates lack of the purity of the rendered protein incorporated in theircardiac muscle movement and death.136 products. Accordingly, increased analytic sensitivity has led many renderers to reconsider accepting horses16 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 17. euthanized using barbiturates. This places renderers pharmaceutical residues in animal remains other thanand those wishing to employ rendering as a means of barbiturates (eg, xylazine) may affect scavengers and candisposal for animals euthanized using pentobarbital in reduce the acceptability of the animal remains for ren-a difficult position, and may result in renderers being derers. Unfortunately, specific guidance from regulatorsreluctant to accept more animal remains than they can regarding the use of such alternatives is limited.reasonably manage without creating residue concerns. The persistence of antimicrobials in animal remainsAlternatives for disposal of animal remains must be presents parallel concerns, particularly for animal re-considered in advance, in case the renderer cannot or mains that will be rendered. While many antimicrobialswill not accept animal remains containing barbiturate may be inactivated or destroyed through the renderingresidues. process, public health concerns associated with antimi- Composting is another means of disposing of ani- crobial resistance, coupled with the enhanced sensitiv-mal remains that is becoming increasingly common. ity of chemical assays and limited regulatory guidanceStudies examining the persistence of barbiturate resi- for renderers, further complicate veterinarians’ respon-dues in composted animal remains are few, but those sibilities for safe remediation.that do exist suggest the persistence of the drugs in Safe handling and disposal of the resulting animalcomposted material. While the implications of this are remains are also critically important when zoonotic dis-still unclear, it does raise questions about potential en- eases, foreign animal diseases, or diseases of concern tovironmental impacts in the case of animal health emer- population health are suspected. Appropriate diagnos-gencies or mass mortality events. tic samples should be collected for testing, regulatory Alternatives to the use of pentobarbital that may re- authorities must be contacted, and the animal remainsduce the risk of secondary toxicity include general an- must be incinerated (if possible). Personal protectiveesthesia followed by nontoxic injectable agents such as equipment and precautions for handling biohazardouspotassium chloride, or the application of physical meth- materials are recommended. Animals that have injuredods such as penetrating captive bolt or gunshot. These humans may require specific actions to be taken de-alternatives, however, are not risk free. For example, pending on local and state laws.AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 17
  • 18. Part II—Methods of EuthanasiaM1. INHALED AGENTS ning box in groups, rather than lining them up single file as needed for electric stunning, improves voluntaryM1.1 COMMON CONSIDERATIONS forward movement, reduces handling stress and elec- Inhaled vapors and gases require a critical concen- tric prod use, and improves meat quality.142tration within the alveoli and blood for effect; thus, all That inhaled agents can produce distress and aver-inhaled methods have the potential to adversely affect sion in people raises concerns for their use in animals,animal welfare because onset of unconsciousness is not in that the US Government Principles for the Utiliza-immediate. Distress may be created by properties of the tion and Care of Vertebrate Animals Used in Testing,agent (eg, pungency, hypoxia, hypercarbia) or by the Research, and Training143 state “Unless the contrary isconditions under which the agent is administered (eg, established, investigators should consider that proce-home cage or dedicated chamber, gradual displacement dures that cause pain or distress in human beings mayor prefilling of the container), and may manifest itself cause pain or distress in other animals.” Interestingly,behaviorally (eg, overt escape behaviors, approach- more than 40% of human children 2 to 10 years oldavoidance preferences [aversion]) or physiologically display distress behaviors during sevoflurane induc-(eg, changes in heart rate, sympathetic nervous system tion, with 17% displaying significant distress and more[SNS] activity, hypothalamic-pituitary axis [HPA] activ- than 30% physically resisting during induction.144 Fearity). Although SNS and HPA activation are well accept- in children undergoing anesthesia may be due to odor,ed as markers of a stress response, these systems are ac- feel of the mask, or a true phobia of the mask.145 Despitetivated in response to both physical and psychological evidence of distress and aversion, inhaled anestheticsstressors and are not necessarily associated with higher- continue to be administered because the benefits asso-order CNS processing and conscious experience by the ciated with their use greatly outweigh any distress and/animal. Furthermore, use of SNS and HPA activation to or aversion they may cause.assess distress during inhalation of euthanasia agents is The suitability of any particular inhaled agent forcomplicated by continued exposure to the agents dur- euthanasia therefore depends largely on distress and/ing the period between loss of consciousness and death. or pain experienced prior to loss of consciousness. Dis- Distress during administration of inhaled agents tress can be caused by handling, specific agent prop-has been evaluated by means of both behavioral assess- erties, or method of administration, such that a one-ment and aversion testing. While overt behavioral signs size-fits-all approach cannot be easily applied. Sufferingof distress have been reported in some studies, oth- can be conceptualized as the product of severity, inci-ers have not consistently found these effects. Through dence, and duration. As a general rule, a gentle deathpreference and approach-avoidance testing, all inhaled that takes longer is preferable to a rapid, but more dis-agents currently used for euthanasia have been identi- tressing death25; however, in some species and underfied as being aversive to varying degrees. Aversion is some circumstances, the most humane and pragmatica measure of preference, and while aversion does not option may be exposure to an aversive agent or condi-necessarily imply that the experience is painful, forcing tion that results in rapid unconsciousness with few oranimals into aversive situations creates stress. The con- no outward signs of distress. Our goal is to identify bestditions of exposure used for aversion studies, however, practices for administering inhaled agents, defining themay differ from those used for stunning or killing. In optimal conditions for transport, handling, and agentaddition, agents identified as being less aversive (eg, Ar selection and delivery to produce the least aversive andor N2 gas mixtures, inhaled anesthetics) can still pro- distressing experience for each species.duce overt signs of behavioral distress (eg, open-mouth The following contingencies are common to all in-breathing) in some species under certain conditions haled euthanasia agents:of administration (eg, gradual displacement). As pre- (1) Time to unconsciousness with inhaled agents isviously noted in the section on consciousness, one of dependent on the displacement rate, container volume,the characteristics of anesthesia in people is feeling as and concentration. An understanding of the principlesif one is having an out-of-body experience, suggesting governing delivery of gases or vapors into encloseda disconnection between one’s sense of self and one’s spaces is necessary for appropriate application of bothawareness of time and space.140 Although we cannot prefill and gradual displacement methods.know for certain the subjective experiences of animals, (2) Loss of consciousness will be more rapid if ani-one can speculate similar feelings of disorientation may mals are initially exposed to a high concentration of thecontribute to the observed signs of distress. agent. However, for many agents and species, forced ex- As for physical methods, the conditions under posure to high concentrations can be aversive and dis-which inhaled agents are administered for euthanasia tressing, such that gradual exposure may be the mostcan have profound effects on an animal’s response and, pragmatic and humane option.thus, agent suitability. Simply placing Sprague-Dawley (3) Inhaled agents must be supplied in purifiedrats into an unfamiliar exposure chamber containing form without contaminants or adulterants, typicallyroom air produces arousal, if not distress.141 Pigs are from a commercially supplied source, cylinder, or tank,social animals and prefer not to be isolated from one such that an effective displacement rate and/or concen-another; consequently, moving them to the CO2 stun- tration can be readily quantified. The direct application18 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 19. of products of combustion or sublimation is not accept- If an animal is not dead, exposure must be repeated orable due to unreliable or undesirable composition and/ followed with another method of euthanasia.or displacement rate. (4) The equipment used to deliver and maintain M1.2 PRINCIPLES GOVERNINGinhaled agents must be in good working order and in ADMINISTRATIONcompliance with state and federal regulations. Leaky or Changes in gas concentration within any enclosedfaulty equipment may lead to slow, distressful death and space involve two physical processes: (1) wash-in ofmay be hazardous to other animals and to personnel. new gas (or washout of existing gas) and (2) the time (5) Most inhaled agents are hazardous to animal constant required for that change to occur within theworkers because of the risk of explosions (eg, ether, container for a known flow rate. These processes areCO), narcosis (eg, halocarbon anesthetics, CO2, as- commonly combined in the practice of anesthesia tophyxiating gases), hypoxia (eg, asphyxiating gases, predict how quickly a change in concentration of anCO), addiction or physical abuse (eg, nitrous oxide inhaled anesthetic will occur within a circle rebreath-[N2O], halocarbon anesthetics), or health effects result- ing circuit.148 An understanding of how these processesing from chronic exposure (eg, N2O, CO, possibly halo- work together is critical for the appropriate applicationcarbon anesthetics). of both gradual displacement and prefill immersion eu- (6) In sick or depressed animals where ventilation thanasia methods.149is decreased, agitation during induction is more likely The rate of change of gas concentration within anybecause the rise in alveolar gas concentration is delayed. enclosed space is a special form of nonlinear changeA similar delayed rise in alveolar gas concentration can known as an exponential process, and as such can bebe observed in excited animals having increased cardiac derived from the wash-in and washout exponentialoutput. Suitable premedication or noninhaled methods functions.150 Briefly, for the wash-in exponential func-of euthanasia should be considered for such animals. tion the quantity under consideration rises toward a (7) Neonatal animals appear to be resistant to hy- limiting value, at a rate that progressively decreases inpoxia, and because all inhaled agents ultimately cause proportion to the distance it still has to rise. In theo-hypoxia, neonatal animals take longer to die than ry, the quantity approaches, but never reaches, 100%.adults.146 Inhaled agents can be used alone in unweaned Conversely, for the wash-out exponential function theanimals to induce loss of consciousness, but prolonged quantity under consideration falls at a rate that progres-exposure time or a secondary method may be required sively decreases in proportion to the distance it still hasto kill the unconscious animal. to fall. Again, in theory, the quantity approaches, but (8) Reptiles, amphibians, and diving birds and never reaches, zero.mammals have a great capacity for holding their breath The exponential wash-in and washout equationsand for anaerobic metabolism. Therefore, induction of are used to derive the time constant (τ) for an en-anesthesia and time to loss of consciousness when in- closed volume or space. This constant is mathemati-haled agents are used may be greatly prolonged. Nonin- cally equal to the enclosed volume or space undergo-haled methods of euthanasia should be considered for ing wash-in or wash-out divided by the rate of flow, orthese species and a secondary method is required to kill displacement, into that space, where τ = volume / flowthe unconscious animal. rate.150,151 Thus, the time constant represents the time (9) Rapid gas flows can produce noise or cold at which the wash-in or washout process would havedrafts leading to animal fright and escape behaviors. If been complete had the initial rate of change continuedhigh flows are required, equipment should be designed as a linear function rather than an exponential func-to minimize noise and gas streams blowing directly on tion.150 As such, the time constant is similar in conceptthe animals. to the half-life, although they are neither identical nor (10) When possible, inhaled agents should be ad- interchangeable.151ministered under conditions where animals are most For the wash-in function, 1(τ) is required for thecomfortable (eg, for rodents, in the home cage; for pigs, concentration of the inflowing gas to rise to 63.2% ofin small groups). If animals need to be combined, they the inflowing gas concentration, 2(τ) are required forshould be of the same species and compatible cohorts, the concentration to rise to 86.5%, and 3(τ) are re-and, if needed, restrained or separated so that they will quired for the concentration to rise to 95%, with ϱ(τ)not hurt themselves or others. Chambers should not required for the gas concentration within the containerbe overloaded and need to be kept clean to minimize to equal the inflowing gas concentration. Conversely,odors that might cause distress in animals subsequently for the washout function, 1(τ) is required for the re-euthanized. maining gas concentration to fall to 36.8% of the orig- (11) Because some inhaled agents may be lighter inal value, 2(τ) are required for gas concentration toor heavier than air, layering or loss of agent may permit fall to 13.5%, 3(τ) are required for gas concentrationanimals to avoid exposure. Mixing can be maximized to fall to 5%, with ϱ(τ) required for gas concentrationby ensuring incoming gas or vapor flow rates are suf- to fall to 0% (Figure 3). The flow, or displacement rate,ficient. Chambers and containers should be as leak free therefore determines the time constant for any givenas possible. enclosed volume, such that increasing the flow rate will (12) Death must be verified following administra- result in a proportional reduction of the wash-in andtion of inhaled agents. This can be done either by ex- washout time constants for any size chamber (and viceamination of individual animals or by adherence to val- versa).idated exposure processes proven to result in death.147 Based on Figure 3, it can be shown that a gradualAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 19
  • 20. rates that can lead to delivery of freezing gas and dry ice snow to the animals as well as regulator icing and cylinder freezing. A distinction must be made between immersion, where animals are directly placed into a gas or vapor contained within a container, and the process of con- trolled atmospheric stunning (CAS) as employed for the commercial stunning of poultry and hogs. Although a complete description of the operation of the commer- cial CAS systems currently in use is beyond the scope of this document, typically the entry point is open to the atmosphere with negligible concentrations of stunning gas present. Unlike immersion, animals are introduced at a controlled rate into a tightly controlled stunning atmospheric gradient, such that CAS can be considered to be a gradual displacement method. M1.3 INHALED ANESTHETICS Overdoses of inhaled anesthetics (eg, ether, halo- thane, methoxyflurane, isoflurane, sevoflurane, des- flurane, enflurane) have been used to euthanize manyFigure 3—Graphic representation of the wash-in and wash-out species.155 Presently, only isoflurane, enflurane, sevoflu-exponential functions, using a hypothetical example of a closedcontainer, originally filled with gas A into which gas B is intro- rane, and desflurane are clinically available in the Unit-duced. The wash-in and wash-out functions are used to deter- ed States, although halothane and methoxyflurane aremine the time constant for the enclosed volume or space. The still available elsewhere in the world. Halothane induc-gas concentration within the container can be readily determinedfrom the time constant, which is calculated by dividing the con- es anesthesia rapidly and is an effective inhaled agenttainer volume by the gas displacement rate. Figure taken from for euthanasia. Enflurane is less soluble in blood thanMeyer RE, Morrow WEM. Carbon dioxide for emergency on-farm halothane, but, because of its lower vapor pressure andeuthanasia of swine. Journal of Swine Health and Production2005;13(4): 210–217 2005. Reprinted with permission. , lower potency, induction rates may be similar to those for halothane. At deep anesthetic planes, convulsionsinflow or displacement rate of 20% of the chamber vol- may occur. Enflurane is an effective agent for euthana-ume per minute represents a time constant (τ) value of sia, but the associated seizure activity may be disturb-5 minutes (1 divided by 0.2/min) regardless of chamber ing to personnel. Isoflurane is less soluble than halo-volume. For example, CO2 displacement rate equivalent thane, and it induces anesthesia more rapidly. However,to 20% of the chamber volume/min, as recommended it has a pungent odor and onset of unconsciousnessby Hornett and Haynes152 and Smith and Harrap,153 is may be delayed due to breath holding. Due to lower po-predicted to increase CO2 concentration from zero to tency, isoflurane also may require more drug to kill an63.2% in 5 minutes (1τ), to 86.5% in 10 minutes (2τ), animal, compared with halothane. Sevoflurane is lessand to 95% in 15 minutes (3τ). An examination of the potent than either isoflurane or halothane and has apublished experimental data of Smith and Harrap con- lower vapor pressure. Anesthetic concentrations can befirms this, where CO2 supplied at a displacement rate of achieved and maintained rapidly but more drug will be22% of chamber volume increased the CO2 concentra- required to kill the animal. Although sevoflurane is re-tion to approximately 64% in 4.5 minutes (1τ for their ported to possess less of an objectionable odor than iso-chamber). Similarly, Niel and Weary154 reported 65% af- flurane, some species may struggle violently and expe-ter 340 seconds (1τ) and 87% after 600 seconds (2τ) for rience apnea when sevoflurane is administered by facea CO2 displacement rate of 17.5% of chamber volume/ mask or induction chamber.156 Like enflurane, sevo-min. Prefill methods will require displacement rates of flurane induces epileptiform electrocortical activity.1573τ to attain 95% of the inflow gas concentration within Desflurane is currently the least soluble potent inhaledthe chamber. anesthetic, but the vapor is quite pungent, which may Thus, gas displacement rate is critical to the hu- slow induction. This drug is so volatile that it couldmane application of inhaled methods, such that an ap- displace O2 and induce hypoxemia during inductionpropriate pressure-reducing regulator and flow meter if supplemental O2 is not provided. Both diethyl ethercombination or equivalent equipment with demon- and methoxyflurane are highly soluble, and may be ac-strated capability for generating the recommended dis- companied by agitation because anesthetic induction isplacement rate for the size container being utilized is quite slow. Diethyl ether is irritating to the eyes, nose,absolutely necessary when compressed gases are used and respiratory airways; poses serious risks due to flam-for euthanasia. Nitrogen, Ar, and CO are all commer- mability and explosiveness; and has been used to createcially supplied in cylinders under high pressure, but a model for stress.158–161CO2 is unique in that it is supplied as a liquefied gas Although inhaled anesthetics are routinely usedunder high pressure. By reducing high pressure at the to produce general anesthesia in humans and animals,cylinder valve, gas flow is made constant to the flow these agents may be aversive and distressful under cer-meter as cylinder pressure decreases during use. With tain conditions. Flecknell et al156 reported violent strug-CO2, the regulator also acts to prevent high gas flow gling accompanied by apnea and bradycardia in rabbits20 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 21. administered isoflurane, halothane, and sevoflurane and there are no controlled studies proving exposure atby mask or induction chamber, and concluded these these concentrations are safe. No NIOSH recommendedagents were aversive and should be avoided whenever exposure limits exist for the three most currently usedpossible. Leach et al162–164 found inhaled anesthetic va- anesthetics (isoflurane, desflurane, and sevoflurane),pors to be associated with some degree of aversion in and, at present, the Occupational Safety and Health Ad-laboratory rodents, with increasing aversion noted as ministration has no permissible exposure limits regu-concentration increased; halothane was least aversive lating these specific agents.for rats, while halothane and enflurane were least aver-sive for mice. Makowska and Weary165 also reported Advantages—(1) Inhaled anesthetics are particu-halothane and isoflurane to be aversive to male Wistar larly useful for euthanasia of smaller animals (< 7 kgrats, but less so than CO2. [15.4 lb]) or for animals in which venipuncture may Anesthetic vapor is inhaled until respiration ceas- be difficult. (2) Inhaled anesthetics can be adminis-es and death ensues. Because the liquid state of most tered by several different methods depending on theinhaled anesthetics is irritating, animals should be ex- circumstances and equipment available (eg, face mask,posed only to vapors. With inhaled anesthetics, animals open drop where the animal is not permitted to directlycan be placed in a closed receptacle containing cotton contact the anesthetic liquid, precision vaporizer, rigidor gauze soaked with an appropriate amount of liquid or nonrigid containers). (3) Halothane, enflurane, iso-anesthetic166 or anesthetic vapor can be introduced from flurane, sevoflurane, desflurane, methoxyflurane, anda precision vaporizer.167 Precision anesthetic vaporizers N2O are nonflammable and nonexplosive under usualtypically are limited to 5% to 7% maximum output be- clinical conditions. (4) Inhaled anesthetics can be use-tween 0.5 and 10 L/min O2 flow rate. Induction time ful as the sole euthanasia agent or as part of a 2-stepwill be influenced by dial setting, flow rate, and size process, where animals are first rendered unconsciousof the container; time to death may be prolonged be- through exposure to inhaled anesthetic agents and sub-cause O2 is commonly used as the vapor carrier gas. sequently killed via a secondary method.The amount of liquid anesthetic required to producea given concentration of anesthetic vapor within any Disadvantages—(1) Inhaled anesthetics are aver-closed container can be readily calculated168; in the case sive to rabbits and laboratory rodents and the sameof isoflurane, a maximum of 33% vapor can be pro- may be true for other species. Animals may struggleduced at 20°C. Sufficient air or O2 must be provided and become anxious during induction of anesthe-during the induction period to prevent hypoxia.166 In sia, with some animals exhibiting escape behaviorsthe case of small rodents placed in a large container, prior to onset of unconsciousness. Should apnea orthere will be sufficient O2 in the chamber to prevent excitement occur, time to loss of consciousness mayhypoxia. Larger species placed in small containers may be prolonged. (2) Ether is irritating, flammable, andinitially need supplemental air or O2.166 explosive. Explosions have occurred when animals, Nitrous oxide is the least potent of the inhalation euthanized with ether, were placed in an ordinaryanesthestics. In humans, the minimum alveolar concen- (not explosion-proof) refrigerator or freezer and whentration (defined as the median effective dose) for N2O bagged animals were placed in an incinerator. (3) In-is 104%; its potency in other species is less than half duction with methoxyflurane is unacceptably slow inthat in humans (ie, approx 200%). Because the effective some species. (4) Because of design limits on vapordose for N2O is above 100% it cannot be used alone at 1 output, precision anesthetic vaporizers may be associ-atmosphere of pressure in any species without produc- ated with a longer wash-in time constant and, thus,ing hypoxia prior to respiratory or cardiac arrest. As a longer induction time; time to death may be pro-result, animals may become distressed prior to loss of longed as O2 is commonly used as the vapor carrierconsciousness. Up to 70% N2O may be combined with gas. (5) Nitrous oxide used alone will create a hypoxicother inhaled gases to speed the onset of anesthesia; atmosphere prior to loss of consciousness and willhowever, the anesthetic contribution of N2O will be support combustion. (6) Personnel and animals mayonly half (20% to 30%) of that expected in humans due be injured by exposure to these agents. There is recog-to its reduced potency in animals.169 nized potential for human abuse of inhaled anesthet- Effective procedures should be in place to reduce ics. (7) Because large amounts of inhaled anestheticsanimal worker exposure to anesthetic vapors.170 Human are absorbed and substantial amounts remain in theworkplace recommended exposure limits were issued body for days,171use of inhaled anesthetics for eutha-in 1977 by the National Institute of Occupational Safety nasia is challenging for food-producing animals due toand Health (NIOSH); concentrations for halogenated potential for tissue residues.inhaled anesthetics are not to exceed 2 ppm (1-hourceiling) when used alone, or 0.5 ppm for halogenated General recommendations—Inhaled anesthetics areanesthetics combined with 25-ppm N2O (time-weight- acceptable with conditions for euthanasia of small ani-ed average during use). The American Conference mals (< 7 kg) where the following contingencies can beof Government Industrial Hygienists has assigned a met: (1) In those species where aversion or overt escapethreshold limit value time-weighted average of 50 ppm behaviors have not been noted, exposure to high con-for N2O, 50 ppm for halothane, and 75 ppm for enflu- centrations resulting in rapid loss of consciousness israne for an 8-hour time-weighted exposure. These con- preferred. Otherwise, gradual fill methods can be used,centrations were established because they were found keeping in mind the effect that chamber volume, flowto be attainable utilizing clinical scavenging techniques rate, and anesthetic concentration will have on the timeAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 21
  • 22. constant and rate of rise of anesthetic concentration. minutes. When used with mink and chinchillas, COInhaled anesthetics can be administered as the sole caused collapse in 1 minute, cessation of breathing ineuthanasia agent or as part of a 2-step process, where 2 minutes, and cardiac arrest in 5 to 7 minutes.181,182animals are first rendered unconscious through inhaled Chalifoux and Dallaire183 evaluated the physiologic andanesthetic agent exposure and then subsequently killed behavioral characteristics of dogs exposed to 6% COby a secondary method. (2) Order of preference is iso- in air, and could not determine the precise time of lossflurane, halothane, sevoflurane, enflurane, methoxyflu- of consciousness. Electroencephalographic recordingsrane, and desflurane, with or without N2O. Nitrous ox- revealed 20 to 25 seconds of abnormal cortical func-ide should not be used alone. Methoxyflurane is accept- tion, and during this period the dogs became agitatedable with conditions only if other agents or methods and vocalized. It is not clear whether these behavioralare not available. Ether is not acceptable for euthanasia. responses are indicative of animal distress; however,(3) Although acceptable, inhaled anesthetics are gen- humans in this phase reportedly are not distressed.172erally not used for larger animals because of cost and Subsequent studies184 have revealed that tranquilizationdifficulty of administration. (4) Exposure of workers to with acepromazine significantly decreases behavioralanesthetics must comply with state and federal occupa- and physiologic responses of dogs euthanized with CO.tional health and safety regulations. Carbon monoxide is noted to be aversive to laboratory rats, but not as aversive as CO2.185M1.4 CARBON MONOXIDE In one study on cats,186 CO from gasoline engine Carbon monoxide is a colorless, odorless gas that exhaust was compared with a combination of 70%is nonflammable and nonexplosive at concentrations CO2 plus 30% O2. Signs of agitation before loss of con-< 12%. Carbon monoxide is a cumulative poison that sciousness were greater for the CO2-plus-O2 combina-produces fatal hypoxemia; it readily combines with he- tion. Time to complete immobilization was greater withmoglobin and blocks uptake of O2 by erythrocytes by CO2 plus O2 (approx 90 seconds) than with CO aloneforming carboxyhemoglobin.172,173 Precisely because it (approx 56 seconds).186 In another study in neonatalis insidious, difficult to detect, and highly toxic even pigs,187 excitation was less likely to precede loss of con-at low concentrations, the lethal properties of CO have sciousness if animals were exposed to a slow rise in COlong been recognized; indeed, approximately 50,000 concentration.emergency room visits for human CO poisoning occur A study of an epidemic of avian influenza in thein the United States annually.174 Netherlands in 2003 compared the use of CO2 with CO In people, the clinical presentation for CO inha- for gassing whole houses of poultry.188 The research-lation is nonspecific, with headache, dizziness, and ers noted that more convulsions were observed in theweakness the most common symptoms of low-level presence of CO and recommended that CO2 was theCO toxicosis. As concentrations of CO increase, these preferred agent for this application due to safety regula-signs may be followed by decreased visual acuity, tin- tions required for the use of CO.nitus, nausea, progressive depression, confusion, andcollapse.175 With higher-level exposure, coma, convul- Advantages—(1) Carbon monoxide induces loss ofsions, and cardiorespiratory arrest may occur.173 Car- consciousness without pain and with minimal discern-bon monoxide stimulates motor centers in the brain, ible discomfort, depending on species. (2) Hypoxemiasuch that loss of consciousness may be accompanied by induced by CO is insidious. (3) Death occurs rapidly ifconvulsions and muscular spasms. Distinct signs of CO concentrations of 4% to 6% are used.toxicosis are not evident until the CO concentration is0.05% in air, and acute signs do not develop until CO Disadvantages—(1) Carbon monoxide is an aver-concentration is approximately 0.2% in air. In humans, sive agent for laboratory rodents and the same may beexposure to 0.32% CO and 0.45% CO for 1 hour will true for other species. (2) Safeguards must be taken toinduce loss of consciousness and death, respectively.176 prevent and monitor exposure of personnel. (3) Electri-Chronic exposure to low concentrations of CO may be cal equipment exposed to CO (eg, lights and fans) musta health hazard, especially with regard to cardiovascular be spark free and explosion proof.disease and teratogenic effects.173,174,177–179 An efficientexhaust or ventilation system is essential to prevent ac- General recommendations—Carbon monoxide iscidental exposure of humans. acceptable with conditions for euthanasia, provided all In the past, mass euthanasia was accomplished by of the following contingencies are met: (1) Personneluse of three different methods for generating CO: (1) using CO must be instructed thoroughly in its use andchemical interaction of sodium formate and sulfuric must understand its hazards and limitations. (2) Theacid, (2) exhaust fumes from gasoline internal com- CO chamber must be of the highest-quality construc-bustion engines, and (3) commercially compressed CO tion and should allow for separation of individual ani-in cylinders. The first 2 techniques are associated with mals. If animals need to be combined, they should be ofsubstantial problems such as production of other gases, the same species, and, if needed, restrained or separatedinadequate production of CO, inadequate gas cooling, so that they will not hurt themselves or others. Cham-inability to quantify delivery rate, and maintenance of bers should not be overloaded and need to be keptequipment. clean to minimize odors that might distress animals Ramsey and Eilmann180 found that a concentra- that are subsequently euthanized. (3) The CO sourcetion of 8% CO caused guinea pigs to collapse in 40 and chamber must be located in a well-ventilated en-seconds to 2 minutes, and death occurred within 6 vironment, preferably out-of-doors. (4) The chamber22 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 23. must be well lighted and must allow personnel direct loss of consciousness, suggesting similar potential forobservation of animals. (5) The CO flow rate should distress.195 These observations are not surprising, asbe adequate to rapidly achieve a uniform CO concen- gradual displacement methods using N2 or Ar, alone ortration of at least 6% after animals are placed in the mixed with other gases, are predicted by the wash-inchamber, except for those species (eg, neonatal pigs) and washout functions to result in prolonged exposurewhere it has been shown that less agitation occurs with to hypoxic conditions.a gradual rise in CO concentration.187 (6) If the cham- In contrast, hypoxia produced by inert gases suchber is inside a room, CO monitors must be placed in as N2 and Ar appears to cause little or no aversion inthe room to warn personnel of hazardous concentra- turkeys196 or chickens197; these animals freely entered ations. (7) It is essential that CO use be in compliance chamber containing < 2% O2 and > 90% Ar. When Arwith state and federal occupational health and safety was used to euthanize chickens, exposure to a chamberregulations. (8) Carbon monoxide must be supplied in prefilled with Ar, with an O2 concentration of < 2%, leda precisely regulated and purified form without con- to EEG changes and collapse in 9 to 12 seconds. Birdstaminants or adulterants, typically from a commercially removed from the chamber at 15 to 17 seconds failedsupplied cylinder or tank. The direct application of to respond to comb pinching. Continued exposure ledproducts of combustion or sublimation is not accept- to convulsions at 20 to 24 seconds. Somatosensory-able due to unreliable or undesirable composition and/ evoked potentials were lost at 24 to 34 seconds, andor displacement rate. As gas displacement rate is critical the EEG became isoelectric at 57 to 66 seconds.198 Withto the humane application of CO, an appropriate pres- turkeys, immersion in 90% Ar with 2% residual O2 ledsure-reducing regulator and flow meter combination or to EEG suppression in 41 seconds, loss of SEP in 44equivalent equipment with demonstrated capability for seconds, and isoelectric EEG in 101 seconds, leadinggenerating the recommended displacement rate for the the authors to conclude exposure times > 3 minutessize container being utilized is absolutely necessary. were necessary to kill all birds.199 Failure to maintain < 2% O2 prolongs survival.200,201 Gerritzen et al202 alsoM1.5 NITROGEN, ARGON reported that chickens did not avoid chambers con- Nitrogen and Ar are odorless, colorless and tasteless taining < 2% O2; birds gradually became unconsciousgases that are inert, nonflammable, and nonexplosive. without showing signs of distress. Chickens202–205 andNitrogen normally comprises 78% of atmospheric air, turkeys196 killed by hypoxia show less head shaking andwhereas Ar comprises less than 1%. These gases func- open-beak breathing than birds exposed to CO2.tion in the current context by displacing air (and the O2 Hypoxia produced by N2 and Ar appears to re-it contains), causing anoxia. Exposure of Sprague-Daw- duce, but not eliminate, aversive responses in pigs. Pigsley rats to severe hypoxic conditions (< 2% O2) using chose to place their head in a hypoxic (< 2% O2, 90%either gas leads to unconsciousness around 90 seconds Ar) chamber containing a food reward, remained withand death after 3 minutes using Ar or 7 minutes us- their head in the chamber until they became ataxic, anding N2141; similar findings have been reported for dogs, freely returned to the chamber once they regained pos-rabbits, and mink.181,182,189,190 Male Sprague-Dawley rats ture.206 In contrast, exposure to 90% Ar, 70% N2/30%become hyperpneic, but can survive for more than 20 CO2, and 85% N2/15% CO2 all resulted in signs of aver-minutes in Ar or N2 at an O2 concentration of 4.9%.191 sion, defined by the authors as escape attempts and Rats are sensitive to even small changes in the gasping; however, the proportion of pigs showing theseconcentration of O2, and are able to detect concentra- behaviors was lowest with Ar.207 Early removal from thetions both lower and higher than the 20.9% normally stunning atmosphere results in rapid regaining of con-found in air.192 Rats and mice allowed to travel be- sciousness, such that exposure times > 7 minutes aretween chambers containing different gases spent most needed to ensure killing with these gases.208of their time in the control chamber (containing air), Mink will also enter into a hypoxic chamber (< 2%but preferred a hypoxic chamber (containing Ar) to a O2, 90% Ar), but will not remain until the point of un-chamber containing CO2; however, the animals stayed consciousness. The duration of hypoxic exposure freelyonly a few seconds in either gas.162–164 Even when rats chosen is similar to the average duration of a dive forwere trained to enter a chamber for a food reward they mink, suggesting they are able to detect hypoxia andtypically refused to enter, or left immediately after en- modify their behavior to avoid detrimental effects.209tering, when the atmosphere was hypoxic (< 2% O2,90% Ar).193 When rats were exposed to gradually de- Advantages—(1) Nitrogen and Ar do not appearcreasing concentrations of O2 and increasing concen- to be directly aversive to chickens or turkeys, and thetrations of Ar, they always left the chamber before los- resulting hypoxia appears to be nonaversive or onlying consciousness (typically when O2 declined to about mildly aversive to these species. Similarly, N2 and Ar7%).194 With N2 flowing at a rate of 39% of chamber gas mixtures do not appear to be directly aversive tovolume/min (τ = 2 minutes 34 seconds), rats collapsed pigs and appear to reduce, but not eliminate, the be-in approximately 3 minutes and stopped breathing in havioral responses to hypoxia. (2) Nitrogen and Ar are5 to 6 minutes; regardless of flow rate, signs of panic nonflammable, nonexplosive, and readily available asand distress were evident before the rats collapsed and compressed gases. (3) Hazards to personnel are mini-died.152 During forced exposure to Ar gradually filling a mal when used with properly designed equipment. (4)chamber at a rate of 50% of the chamber volume/min (τ Argon and N2-CO2 gas mixtures are heavier than air and= 2 minutes), male Sprague-Dawley rats showed open- can be contained within an apparatus into which ani-mouthed breathing and seizure-like behavior prior to mals and birds can be lowered or immersed.207AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 23
  • 24. Disadvantages—(1) Hypoxia resulting from ex- to formation of carbonic acid on respiratory and ocularposure to these gases is aversive to rats, mice, and membranes, (2) production of so-called air hunger andmink. (2) Based on the wash-in and washout func- a feeling of breathlessness, and (3) direct stimulation oftions, gradual displacement methods using N2 or Ar, ion channels within the amygdala associated with thealone or mixed with other gases, may result in expo- fear response.sure to hypoxic conditions prior to loss of conscious- Carbon dioxide may cause pain due to the forma-ness. Loss of consciousness will be preceded by open- tion of carbonic acid when it contacts moisture on themouth breathing and hyperpnea, which may be dis- respiratory and ocular membranes. In humans, rats,tressing for nonavian species. (3) Reestablishing a low and cats, most nociceptors begin to respond at CO2 con-concentration of O2 (ie, 6% or greater) in the chamber centrations of approximately 40%.218–221 Humans reportbefore death will allow immediate recovery.206,208,210 discomfort begins at 30% to 50% CO2, and intensifies(4) Exposure times > 7 minutes are needed to ensure to overt pain with higher concentrations.222–224 Inhaledkilling of pigs. (5) As with CO2, rats euthanized with irritants are known to induce a reflex apnea and heartAr demonstrate alveolar hemorrhage consistent with rate reduction, and these responses are thought to re-terminal asphyxiation.195 (6) Argon costs about three duce transfer of harmful substances into the body.225 Intimes as much as N2. (7) These gases tend to cause rats, 100% CO2 elicits apnea and bradycardia, but CO2more convulsive wing flapping in poultry than CO2 in at concentrations of 10%, 25%, and 50% does not,226air mixtures. suggesting gradual displacement methods are less like- ly to produce pain prior to unconsciousness in rodents. General recommendations—Hypoxia resulting from Carbon dioxide has a key role as a respiratoryexposure to Ar or N2 gas mixtures is acceptable with stimulant, and elevated concentrations are known toconditions for euthanasia of chickens and turkeys. cause profound effects on the respiratory, cardiovascu-Likewise, hypoxia resulting from Ar or N2-CO2 gas lar, and sympathetic nervous systems.227–229 In humans,mixtures is acceptable with conditions for euthanasia air hunger begins at concentrations as low as 8% andof pigs, provided animals can be directly placed into a this sensation intensifies with higher concentrations,< 2% O2 atmosphere and exposure times > 7 minutes becoming severe at approximately 15%.230–232 With mildare used. Use of Ar or N2 is unacceptable for other increases in inspired CO2, increased ventilation resultsmammals. These gases create an anoxic environment in a reduction or elimination of air hunger, but therethat is distressing for some species and aversive to labo- are limits to this compensatory mechanism such thatratory rodents and mink; other methods of euthanasia air hunger may reoccur during spontaneous breathingare preferable for these species. Argon or N2 hypoxia, with moderate hypercarbia and hypoxemia.233–235 Add-defined as O2 < 2%, could be used to kill these animals ing O2 to CO2 may or may not preclude signs of dis-after they are rendered unconscious via an acceptable tress.224,236–238 Supplemental O2 will, however, prolongmethod, although prolonged exposure may be neces- time to hypoxemic death and may delay onset of un-sary to ensure death. consciousness. Nitrogen, Ar, and gas mixtures containing these Although CO2 exposure has the potential to pro-gases must be supplied in a precisely regulated and pu- duce a stress response, interpretation of the subjec-rified form without contaminants or adulterants, typi- tive experiences of animals is complicated. Borovsky239cally from a commercially supplied cylinder or tank. found an increase in norepinephrine in rats followingThe direct application of products of combustion or 30 seconds of exposure to 100% CO2. Similarly, Reed240sublimation is not acceptable due to unreliable or un- exposed rats to 20 to 25 seconds of CO2, which wasdesirable composition or displacement rate. As gas dis- sufficient to render them recumbent, unconscious, andplacement rate is critical to the humane application of unresponsive, and observed 10-fold increases in vaso-these gases, an appropriate pressure-reducing regulator pressin and oxytocin concentrations. Indirect measuresand flow meter combination or equivalent equipment of sympathetic nervous system activation, such as el-with demonstrated capability for generating the recom- evated heart rate and blood pressure, have been compli-mended displacement rate for the size container being cated by the rapid depressant effects of CO2 exposure.utilized is absolutely necessary. Activation of the hypothalamic pituitary axis has also been examined during CO2 exposure. Prolonged ex-M1.6 CARBON DIOXIDE posure to low concentrations of CO2 (6% to 10%) has Inhalation of CO2 causes respiratory acidosis and been found to increase corticosterone in rats241,242 andproduces a reversible anesthetic state by rapidly de- cortisol in dogs.243 In a single-blind study in healthy hu-creasing intracellular pH.211 Both basal and evoked neu- man volunteers, a single breath of 35% CO2 was foundral activity are depressed soon after inhalation of 100% to result in elevated cortisol concentrations and expo-CO2.211–214 Inhalation of CO2 at a concentration of 7.5% sure was associated with an increase in fear.244 It hasincreases pain threshold, and concentrations of 30% been suggested that responses to systemic stressors as-and higher cause deep anesthesia and death with pro- sociated with immediate survival, such as hypoxia andlonged exposure.153,154,215–217 Methods to administer CO2 hypercapnia, are likely directly relayed from brainsteminclude placing animals directly into a closed, prefilled nuclei and are not associated with higher-order CNSchamber containing CO2, or exposure to a gradually in- processing and conscious experience.245 In fact, Kc etcreasing concentration of CO2. al246 found that hypothalamic vasopressin-containing Carbon dioxide has the potential to cause distress neurons are similarly activated in response to CO2 ex-in animals via three different mechanisms: (1) pain due posure in both awake and anesthetized rats. As stated24 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 25. previously, assessment of the animal’s response to in- ing that aversive responses to CO2 in rodents, and po-haled agents, such as CO2, is complicated by continued tentially other species, are mediated in part by an innateexposure during the period between loss of conscious- fear response. Further studies defining the presence ofness and death. ASICs and their role in CO2-induced fear in other ro- Distress during CO2 exposure has also been ex- dent strains, as well as other animal species, are war-amined by means of behavioral assessment and aver- ranted.sion testing. Variability in behavioral responses to CO2 As with other inhaled agents, time to unconscious-has been reported for rats and mice,152–154,195,237,247–249 ness with CO2 is dependent on the displacement rate,pigs,206,250–253 and poultry.196,202–205,254–257 While signs of container volume, and concentration used. In rats, un-distress have been reported as occurring in animals in consciousness is induced in approximately 12 to 33some studies, other researchers have not consistently seconds with 80% to 100% CO2 and 40 to 50 secondsobserved these effects. This may be due to variations with 70% CO2.237,263 Similarly, a rapidly increasing con-in methods of gas exposure and types of behaviors as- centration (flow rate > 50% of the chamber volume persessed, as well as strain variability. minute) induces unconsciousness in only 26 to 48 sec- Using preference and approach-avoidance testing, onds.153,154,195,238,247 Leake and Waters217 found that dogsrats and mice show aversion to CO2 concentrations exposed to 30% to 40% CO2 were anesthetized in 1 tosufficient to induce unconsciousness,162,163 and are 2 minutes. For cats, inhalation of 60% CO2 results inwilling to forgo a palatable food reward to avoid expo- loss of consciousness within 45 seconds, and respira-sure to CO2 concentrations of approximately 15% and tory arrest within 5 minutes.264 For pigs, exposure tohigher165,193 after up to 24 hours of food deprivation.236 60% to 90% CO2 causes unconsciousness in 14 to 30Mink will avoid a chamber containing a desirable novel seconds,210–212,250 with unconsciousness occurring priorobject when it contains 100% CO2.258 In contrast to to onset of signs of excitation.210,214 Euthanasia via ex-other species, a large proportion of chickens and tur- posure to CO2 has been described for individual birdskeys will enter a chamber containing moderate concen- and small groups,265 and its application to euthanasia oftrations of CO2 (60%) to gain access to food or social chickens, turkeys, and ducks has been studied exten-contact.197,202,250 Following incapacitation and prior to sively, resulting in information about times to collapse,loss of consciousness, birds in these studies show be- unconsciousness and death, loss of somatosensoryhaviors such as open-beak breathing and head-shaking; evoked potentials, and changes in EEG. Leghorn chicksthese behaviors, however, may not be associated with 7 days of age collapsed in 12 seconds after exposure todistress because birds do not withdraw from CO2 when 97% CO2.248 Raj201 found that 2 minutes’ exposure tothese behaviors occur.203 Thus, it appears that birds are 90% CO2 was sufficient to kill day-old chicks exposedmore willing than rodents and mink to tolerate CO2 in batches. Broilers 5 weeks of age collapsed an averageat concentrations that are sufficient to induce loss of of 17 seconds after entering a tunnel filled with 60%posture, and that loss of consciousness follows shortly CO2.202afterwards. Unlike N2 and Ar, which must be held within a Genetics may play a role in CO2 response variabil- very tight range of concentration for effective euthana-ity. Panic disorder in humans is genetically linked to sia, CO2 can render poultry unconscious and kill overenhanced sensitivity to CO2.259 The fear network, com- a wide range of concentrations. In tests where it took 8prising the hippocampus, the medial prefrontal cortex, seconds to achieve the target gas concentration, broilersthe amygdala, and its brainstem projections, appears to and mature hens collapsed in 19 to 21 seconds at 65%be abnormally sensitive to CO2 in these patients.260 The CO2 and 25 to 28 seconds at 35% CO2.266 In a gradual-genetic background of some pigs, especially excitable fill study, ducks and turkeys lost consciousness beforelines such as the Hampshire and German Landrace, has 25% CO2 was reached and died after the concentrationbeen associated with animals that react poorly to CO2 reached 45%.254 At 49% CO2, EEG suppression, loss ofstunning, while calmer lines combining the Yorkshire somatosensory evoked potentials (SEPs), and EEG si-or Dutch Landrace conformations show much milder lence occurred in 11, 26, and 76 seconds in chickens.267reactions.261 Given a choice, Duroc and Large White In turkeys, EEG suppression took place in an average ofpigs will tolerate 30% CO2 to gain access to a food re- 21 seconds at 49% CO2, but was reduced to 13 secondsward, but will forgo the reward to avoid exposure to at 86% CO2. In the same report, time to loss of SEPs was90% CO2, even after a 24-hour period of food depri- not affected by gas concentration, averaging 20, 15, andvation.206,250 A shock with an electric prod, however, 21 seconds, but time to EEG silence was concentrationis more aversive to Landrace X Large White pigs than dependent (ie, 88, 67, and 42 seconds for 49%, 65%,inhaling 60% or 90% CO2, with pigs inhaling 60% CO2 and 86% CO2, respectively).268willing to reenter the crate containing CO2.251 Until fur- As a general rule, a gentle death that takes longerther research is conducted, one can conclude that use is preferable to a rapid, but more distressing death.25of CO2 may be humane for certain genetic lines of pigs Gradual-fill CO2 exposure causes aversion in rodentsand stressful for others.261 beginning at approximately a 15% concentration and Recent studies involving mice have found regions lasting to onset of unconsciousness. If an appropriateof the amygdala associated with fear behavior to con- gradual displacement rate is used, animals will losetain acid-sensing ion channels (ASICs) sensitive to el- consciousness before CO2 concentrations become pain-evated CO2.262 Fear behaviors and aversion in response ful.195 A 20%/min gradual displacement produces un-to CO2 exposure were reduced in mice in which the consciousness in 106 seconds at a CO2 concentration ofASIC receptors were eliminated or inhibited, suggest- 30%152,154,224,238; a slower 10%/min displacement increas-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 25
  • 26. es time to onset of unconsciousness to 156 seconds at within species, strains, and breeds, making broad gener-a CO2 concentration of 21%.195 For poultry, immersion alizations difficult. (2) Carbon dioxide, whether admin-into relatively low concentrations or exposure to CO2 istered by prefill or gradual displacement methods, canconcentrations producing a gradual induction of un- be aversive to some species, and therefore potential ex-consciousness reduces convulsions compared with im- ists to cause distress. (3) Because CO2 is heavier than air,mersion into N2 or Ar.204,269 Carbon dioxide may invoke layering of gas or incomplete filling of a chamber mayinvoluntary (unconscious) motor activity in birds, such permit animals to climb or raise their heads above theas flapping of the wings or other terminal movements, effective concentrations and avoid exposure. (4) Imma-which can damage tissues and be disconcerting for ob- ture individuals and some aquatic and burrowing speciesservers248,270; wing flapping is less with CO2 than with may have extraordinary tolerance for CO2. (5) ReptilesN2 or Ar.269 and amphibians may breathe too slowly for the use of Due to respiratory adaptations in immature ani- CO2. (6) Euthanasia by exposure to CO2 with O2 sup-mals, reptiles, amphibians, and some burrowing and plementation may take longer than euthanasia by otherdiving species (eg, lagomorphs, mustelids, aquatic means.224,237,238 (7) Induction of loss of consciousness atbirds, nonhatched birds, newly hatched chicks), high concentrations < 80% may produce postmortem pulmo-CO2 concentrations, combined with extended expo- nary and upper respiratory tract lesions.224,275 (8) Dry icesure times, follow-up exposure to hypoxemia, or a sec- and liquid CO2 are potential sources of distress or injuryondary euthanasia method, may be required to ensure if permitted to directly contact animals.unconsciousness and death. High CO2 concentrations(> 60%) and extended exposure times (> 5 minutes) General recommendations—Carbon dioxide is ac-are required for effective euthanasia of newly hatched ceptable with conditions for euthanasia in those specieschickens.201,271 On the day of birth, rats and mice ex- where aversion or distress can be minimized. Carbon di-posed to 100% CO2 required exposure times of 35 and oxide exposure using a gradual fill method is less likely50 minutes, respectively, to ensure death. By 10 days of to cause pain due to nociceptor activation by carbonicage, exposure times of 5 minutes were sufficient to en- acid prior to onset of unconsciousness; a displacementsure death.272,273 For adult mink, 5 minutes of exposure rate from 10% to 30% of the chamber volume/min isis sufficient to ensure death using 100% CO2, but not recommended.25,152,193,195 Whenever gradual displace-using 70% CO2.181 Rabbits of the genus Oryctolagus also ment methods are used, CO2 flow should be maintainedhave prolonged survival times when exposed to CO2.274 for at least 1 minute after respiratory arrest.153 If ani- Inhaled halocarbon anesthetics have been pro- mals need to be combined, they should be of the sameposed as alternatives to CO2 for rodent euthana- species and, if needed, restrained so that they will notsia.25,165,167 However, inhaled anesthetics also produce hurt themselves or others. Immature animals must bevarying degrees of aversion in rodents,162–165 and are as- exposed to high concentrations of CO2 for an extendedsociated in other animals and humans with aversion, period of time to ensure death. Oxygen administereddistress, and escape behaviors during anesthetic induc- together with CO2 appears to provide little advantagetion. Uncertainty exists as to the feasibility of substi- and is not recommended for euthanasia.tuting inhaled anesthetic agents for CO2 with respect The practice of immersion, where conscious ani-to animal welfare and human health and safety.25 Time mals are placed directly into a container prefilled withto death may be prolonged as O2 is commonly used as 100% CO2, is unacceptable. A 2-step process, where ani-the vapor carrier gas with precision anesthetic vapor- mals are first rendered unconscious and then immersedizers. Because large amounts of inhaled anesthetics are into 100% CO2, is preferred when gradual displacementabsorbed and substantial amounts remain in the body methods cannot be used. Immersion of poultry in lesserfor days, even after apparent recovery,171 euthanasia via concentrations is acceptable with conditions as it doesinhaled anesthetics is unsuitable for food-producing not appear to be distressing.animals because of the potential for tissue residues. Ef- Carbon dioxide and CO2 gas mixtures must be sup-fective procedures should be in place to reduce worker plied in a precisely regulated and purified form withoutexposure to anesthetic vapors. Careful and deliberate contaminants or adulterants, typically from a commer-consideration of the consequences associated with this cially supplied cylinder or tank. The direct applicationproposal is warranted before this recommendation can of products of combustion or sublimation is not accept-be made. able due to unreliable or undesirable composition and/ or displacement rate. As gas displacement rate is critical Advantages—(1) The rapid depressant, analgesic, to the humane application of CO2, an appropriate pres-and anesthetic effects of CO2 are well established. (2) sure-reducing regulator and flow meter or equivalentCarbon dioxide is readily available in compressed gas equipment with demonstrated capability for generatingcylinders. (3) Carbon dioxide is inexpensive, nonflam- the recommended displacement rates for the size con-mable, and nonexplosive and poses minimal hazard to tainer being utilized is absolutely necessary.personnel when used with properly designed equip-ment. (4) Carbon dioxide does not result in accumula- M2. NONINHALED AGENTStion of toxic tissue residues in animals from which foodis produced. M2.1 COMMON CONSIDERATIONS Noninhaled agents of euthanasia include chemi- Disadvantages—(1) Substantial and conflicting dif- cal agents that are introduced into the body by meansferences in response to CO2 inhalation exist between and other than through direct delivery to the respiratory26 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 27. tract. The primary routes of their administration are thanasia. It is usually the most desirable method whenparenteral injection, topical application, and immer- it can be performed without causing fear or distress insion. When it is being determined whether a particular the animal. When appropriately administered, accept-drug and route of administration are appropriate for eu- able injectable euthanasia agents result in smooth lossthanasia, consideration needs to be given to the species of consciousness prior to cessation of cardiac and/orinvolved, the pharmacodynamics of the chemical agent, respiratory function, minimizing pain and distress todegree of physical or chemical restraint required, po- the animal. However, heightened awareness for per-tential hazards to personnel, consequences of intended sonnel safety is imperative when using injectable eu-or unintended consumption of the animal’s remains by thanasia agents because needle-stick injuries involvinghumans and other animals, and potential hazards to the these drugs have been shown to result in adverse effectsenvironment from chemical residues. Many noninhaled (41.6% of the time); 17% of these adverse effects wereeuthanasia agents can induce a state of unconscious- systemic and severe.280ness during which minimal vital functions are evident Intravenous injections deliver euthanasia agentsbut from which some animals may recover. Therefore, directly into the vascular system, allowing for rapidas for any euthanasia method, death must be confirmed distribution of the agent to the brain or neural cen-prior to final disposition of the animal’s remains. ters, resulting in rapid loss of consciousness (for some invertebrates with closed circulatory systems, intra-M2.1.1 Compounding hemolymph injection is considered analogous to IV While several euthanasia agents (eg, barbiturates, injection).281 When the restraint necessary for givingbarbiturate combinations, Tributameb [not currently be- an animal an IV injection is likely to impart added dis-ing manufactured in the United States due to concerns tress to the animal or pose undue risk to the operator,with the manufacturing process, although the approved sedation, anesthesia, or an acceptable alternate routeNew Animal Drug Application has been retained], and or method of administration should be used. Aggres-T-61c [withdrawn from the market in the United States sive or fearful animals should be sedated prior to re-in 1991; consequently, it is no longer commercially straint for IV administration of the euthanasia agent.available in this country]) have been approved or are Paralytic immobilizing agents (eg, neuromuscularin review by the FDA Center for Veterinary Medicine blocking agents) are unacceptable as a sole means of(FDA-CVM), some commonly used injectable euthana- euthanasia, because animals under their influence re-sia drugs are not approved, but are compounded from main awake and able to feel pain. Having said this,bulk drugs. These include chloral hydrate, magnesium there may be select circumstances (eg, for wild or feralsulfate, and some formulations of potassium chloride. animals) where the administration of paralytic agentsThe FDA-CVM’s most recent version of the Compliance (eg, neuromuscular blocking agents) may be the mostPolicy Guide on compounding of drugs for use in ani- rapid and humane means of restraint prior to euthana-mals states that compounding from bulk drugs, except sia due to their more rapid onset compared with otherthose specifically addressed for regulatory discretion by immobilizing agents.282 In such situations, paralyticthe FDA, raises concerns and may result in regulatory immobilizing agents may only be used if the chosenoversight.276 Use of compounded euthanasia drugs that method of euthanasia (eg, captive bolt, IV injection ofmay create human or animal health risks (eg, uninten- euthanasia solution) can be applied immediately fol-tional ingestion by other animals) is of concern. lowing immobilization. Paralytic immobilizing agents must never be used as a sole means of euthanasia, norM2.1.2 Residue/Disposal Issues should they be used if delay is expected between im- Animals euthanized by chemical means must never mobilization and euthanasia.enter the human food chain and should be disposed of When intravascular administration is consideredin accord with local, state, and federal laws. Disposal of impractical or impossible, IP or intracoelomic adminis-euthanized animals has become increasingly problematic tration of a nonirritating283 barbiturate or other approvedbecause most rendering facilities will no longer take ani- solution is acceptable. Intracoelomic administration ofmals euthanized with agents that pose residue hazards buffered tricaine methanesulfonate (MS 222d,e) is accept-(eg, barbiturates). The potential for ingestion of eutha- able for some poikilotherms. When injectable euthana-nasia agents is an important consideration in the eutha- sia agents are administered into the peritoneal or coe-nasia of animals that are disposed of in outdoor settings lomic cavities, vertebrates may be slow to pass throughwhere scavenging by other animals is possible277 or when stages I and II of anesthesia.284 Accordingly, they shouldeuthanized animals are fed to zoo and exotic animals.278 be placed in small enclosures in quiet areas to minimizeVeterinarians and laypersons have been fined for causing excitement and trauma. Intra-abdominal administrationaccidental deaths of endangered birds that ingested ani- of euthanasia agents is an acceptable means of delivery inmal remains that were poorly buried.138 Environmental invertebrates with open circulatory systems.warnings must now be included on animal euthanasia In anesthetized mice, retrobulbar injection of nodrugs approved by the FDA-CVM.279 more than 200 µL of injectable anesthetic solution (ketamine:xylazine) is acceptable with conditions, re-M2.2 ROUTES OF ADMINISTRATION sulting in death within 5 seconds of cessation of injec- tion.285 Intraosseous administration of some euthanasiaM2.2.1 Parenteral Injection solutions to awake animals may cause pain due to the The use of injectable euthanasia agents is one of viscosity of the agent, chemical irritation, or other rea-the most rapid and reliable methods of performing eu- sons.286 Administration of analgesics, slower injection ofAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 27
  • 28. euthanasia agent, and other strategies that may reduce means of efficient delivery of euthanasia agents fordiscomfort should be used where possible when admin- most animals. Exceptions include animals with highlyistering euthanasia agents through pre-existing intraos- permeable skin to which nonirritating, rapidly ab-seous catheters.287 Placement of intraosseous (greater sorbed agents are applied (eg, amphibians euthanizedtrochanter of the femur, greater tubercle of the humerus, with benzocaine gel). Currently there are no topicalmedial aspect of the proximal tibia) catheters for admin- euthanasia agents that are US FDA approved for anyistration of euthanasia agents and intracardiac, intrahe- species.patic, intrasplenic, or intrarenal injections are acceptableonly when performed on anesthetized or unconscious M2.2.4 Oral Administrationanimals (with the exception of intrahepatic injections in The oral route has several disadvantages when con-cats as discussed in the Companion Animals section of sidered for administration of euthanasia agents, includ-the text). These routes are not acceptable in awake mam- ing lack of established drugs and doses, variability inmals and birds due to the difficulty and unpredictability agent bioavailability and rate of absorption, potentialof performing the techniques accurately with minimal difficulty of administration (including potential for as-discomfort. In some poikilotherms for which intracardi- piration), and potential for loss of agent through vomit-ac puncture is the standard means of vascular access (eg, ing or regurgitation (in species that are capable of thesesome snakes and other reptiles), intracardiac administra- functions). For these reasons, the oral route is generallytion of euthanasia solutions in awake animals is accept- unacceptable as a sole means of euthanasia, but may beable. With the exceptions of IM delivery of ultrapotent an appropriate way to deliver sedatives prior to admin-opioids (ie, etorphine and carfentanil) and IM delivery of istration of parenteral euthanasia agents.select injectable anesthetics, IM, SC, intrathoracic, intra-pulmonary, intrathecal, and other nonvascular injections M2.3 BARBITURIC ACID DERIVATIVESare not acceptable routes of administration for injectable Barbiturates depress the CNS in descending order, be-euthanasia agents in awake animals. ginning with the cerebral cortex, with loss of conscious- ness progressing to anesthesia. With an overdose, deepM2.2.2 Immersion anesthesia progresses to apnea due to depression of the Euthanasia of finfish and some aquatic amphibians respiratory center, and this is followed by cardiac arrest.and invertebrates must take into account the vast dif- All barbituric acid derivatives used for anesthesia areferences in metabolism, respiration, and tolerance to acceptable for euthanasia when administered IV. There iscerebral hypoxia among the various aquatic species. a rapid onset of action, and loss of consciousness inducedBecause aquatic animals have diverse physiologic and by barbiturates results in minimal or transient pain as-anatomic characteristics, optimal methods for delivery sociated with venipuncture. Desirable barbiturates areof euthanasia agents will vary. In many situations, the those that are potent, nonirritating, long acting, stable inimmersion of aquatic animals in water containing eu- solution, and inexpensive. Sodium pentobarbital best fitsthanasia agents is the best way to minimize pain and these criteria and is most widely used, although othersdistress. The response of aquatic animals to immersion such as secobarbital are also acceptable.agents can vary with species, concentration of agent,and quality of water; consideration of these factors Advantages—(1) A primary advantage of barbi-should be made when selecting an appropriate eutha- turates is speed of action. This effect depends on thenasia agent. Immersion agents added to water may be dose, concentration, route, and rate of the injection. (2)absorbed by multiple routes, including across the gills, Barbiturates induce euthanasia smoothly, with minimalvia ingestion, and/or through the skin. discomfort for the animal. (3) Barbiturates are less ex- Ideally, immersion agents added to water will be pensive than many other euthanasia agents. (4) Foodnonirritating to skin, eyes, and oral and respiratory tis- and Drug Administration–approved barbiturate-basedsues and will result in rapid loss of consciousness (often, euthanasia solutions are readily available for dogs andbut not always, measured as a loss of righting response) horses (use for other species is extralabel).with minimal signs of distress or avoidance behavior.Currently there are no US FDA-approved drugs for the Disadvantages—(1) Intravenous injection is neces-euthanasia of aquatic animals. United States Environ- sary for best results and this requires trained personnel.mental Protection Agency (EPA)–registered agents for (2) Each animal must be appropriately restrained. (3)poisoning finfish (eg, rotenone, antimycin) are not rec- Current federal drug regulations require strict account-ommended as euthanasia agents, because their mecha- ing for barbiturates, and these must be used under thenisms of action and times to death do not fit the criteria supervision of personnel registered with the US Drugfor euthanasia. Additionally, the use of these agents re- Enforcement Administration (DEA). Extralabel use re-quires a restricted pesticide applicator’s license and ex- quires the drug be used by or under the supervision oftralabel use of these agents is a violation of federal law. a veterinarian. (4) An aesthetically objectionable termi-Agents approved by the FDA as tranquilizers and anes- nal gasp may occur in unconscious animals. (5) Somethetics for finfish (eg, Finquel,d Tricaine-Se) have been animals may go through an excitatory phase that mayused extralabel as euthanasia agents for aquatic animals. be distressing to observers. (6) These drugs tend to per- sist in the animal’s remains and may cause sedation orM2.2.3 Topical Application even death of animals that consume the body. (7) Tissue Absorption of topically applied agents is slow and artifacts (eg, splenomegaly) may occur in some speciesvariable, making topical application an unacceptable euthanized with barbiturates.28 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 29. General recommendations—The advantages of us- via peripheral vein was evident. This effect was almosting barbiturates for euthanasia in dogs and cats far completely eliminated by addition of lidocaine. The ad-outweigh the disadvantages. Intravenous injection of dition of chloroquine and lidocaine also lowers the dos-a barbituric acid derivative is the preferred method age of embutramide required for euthanasia.291 Deathfor euthanasia of dogs, cats, other small animals, and from Tributame results from severe CNS depression,horses. Barbiturates are also acceptable for all other hypoxia, and circulatory collapse.species of animals if circumstances permit their use. Tributame produces unconsciousness in dogs inIntraperitoneal or intracoelomic injection may be used fewer than 30 seconds, with death occurring within 2in situations when an IV injection would be distressful, minutes; agonal breathing may occur in 60% to 70% ofdangerous, or difficult due to small patient size. Intra- patients.293 Injection is to be given IV over a period ofcardiac (in mammals and birds), intrasplenic, intrahe- 10 to 15 seconds through a preplaced catheter or hypo-patic, and intrarenal injections must only be used if the dermic needle at a dosage of 1 mL for each 5 lbs (0.45animal is unconscious or anesthetized (with the excep- mL/kg [0.2 mL/lb]).tion of intrahepatic injections in cats as discussed in theCompanion Animals section of the text). Advantages—(1) Tributame has a rapid onset of ac- tion. This effect depends on the dose, concentration,M2.4 PENTOBARBITAL COMBINATIONS route, and rate of the injection. (2) Tributame induces Several euthanasia products combine a barbituric euthanasia smoothly, with minimal discomfort to theacid derivative (usually sodium pentobarbital) with local animal. (3) Schedule III status makes Tributame some-anesthetic agents, other CNS depressants (eg, phenytoin, what simpler to obtain, store, and administer thanethanol), or agents that metabolize to pentobarbital. Al- Schedule II drugs such as sodium pentobarbital.though some of the additives are slowly cardiotoxic, eu-thanasia makes this pharmacologic effect inconsequen- Disadvantages—(1) At the time of compilation oftial. These combination products are listed by the DEA this report, while Tributame is FDA approved for use inas schedule III drugs, making them somewhat simpler to dogs, it is not currently being manufactured. (2) Intra-obtain, store, and administer than schedule II drugs such venous injection by trained personnel is necessary. (3)as sodium pentobarbital. The pharmacologic properties Each animal must be individually restrained. (4) Aes-and recommended use of euthanasia products that com- thetically objectionable agonal breathing may occur inbine sodium pentobarbital with agents such as lidocaine unconscious animals. (5) The component drugs tend toor phenytoin are interchangeable with those of pure bar- persist in the animal’s remains and may cause sedationbituric acid derivatives. or even death of animals that consume the body. Mixing of pentobarbital with a neuromuscularblocking agent in the same injection apparatus is not an General recommendations—If it becomes available,acceptable approach to euthanasia because of the po- Tributame is an acceptable euthanasia drug for dogstential for the neuromuscular blocking agent to induce provided that it is administered IV by a highly skilledparalysis prior to onset of unconsciousness. person at recommended dosages and at proper injec- tion rates. If barbiturates are not available, its extralabelM2.5 TRIBUTAME use in cats may be considered; however, adverse reac- Tributame euthanasia solution is an injectable, non- tions (ie, agonal breathing) have been reported and thebarbiturate euthanasia agent with each milliliter contain- current FDA-approved Tributame label recommendsing 135 mg of embutramide, 45 mg of chloroquine phos- against its use in cats. Routes of administration of Trib-phate USP and 1.9 mg lidocaine USP dissolved in water , utame other than IV injection are not acceptable.and ethyl alcohol. The final formulation has a teal bluecolor with the bittering agent, denatonium benzoate, M2.6 T-61added to minimize the risk of the solution being ingest- T-61 is an injectable, nonbarbiturate, nonnarcoticed accidentally. Tributame was approved by the FDA in mixture of embutramide, mebozonium (mebenzo-2005 as an IV agent for euthanasia of dogs, and embutra- nium) iodide, and tetracaine hydrochloride.293 Em-mide was classified as a schedule III controlled substance butramide induces narcosis and respiratory depression,in 2006, making Tributame a C-III controlled agent.288–290 while mebozonium causes nondepolarizing muscular Embutramide is a derivative of γ-hydroxybutyrate paralysis.294 Concern has been expressed that the para-that was investigated as a general anesthetic in the late lytic effect of mebozonium occurs before embutramide-1950s, but was never used as a pharmaceutical agent induced unconsciousness, creating a potential for an-due to a poor margin of safety, with severe cardiovas- imal distress prior to loss of consciousness, as mani-cular effects including hypotension, myocardial depres- fested by muscular activity and/or vocalization duringsion, and ventricular dysrhythmias.291 Embutramide injection. However, electrophysiologic studies in dogscan be injected alone to cause death, but the time until and rabbits have shown that loss of consciousness anddeath can exceed 5 minutes. Subsequently, chloroquine loss of motor activity occur simultaneously followingphosphate, an antimalarial drug with profound cardio- T-61 injection.295 Although many consider the aestheti-vascular depressant effects, was added to embutramide, cally unpleasant reactions of dogs to T-61 injectionand studies verified a significantly shorter time until to be similar to dysphoria seen during the inductiondeath.291,292 Studies on dogs showed this combination phases of anesthesia, the behavior demonstrated dur-of two drugs to be effective, but when tested for eu- ing these reactions can cause distress in personnel wit-thanasia of cats, a substantial response to IV injection nessing euthanasia. Because of these concerns, T-61 hasAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 29
  • 30. been voluntarily withdrawn from the market by the M2.8 DISSOCIATIVE AGENTS ANDmanufacturer and is no longer manufactured or com- α2-ADRENERGIC RECEPTOR AGONISTSmercially available in the United States, although it is Injectable dissociative agent and α2-adrenergic re-available in Canada and other countries. T-61 should be ceptor agonists induce rapid loss of consciousness, andadministered only IV and at carefully monitored rates sometimes muscle relaxation, prior to surgery, dentistry,of injection to avoid dysphoria during injection. or other procedures. These agents are sometimes given prior to administration of euthanasia solutions to mini- Advantages—(1) T-61 has a rapid onset of action mize animal distress, facilitate restraint, and/or provideand has been used to euthanize dogs, cats, horses, labo- a more aesthetic euthanasia environment for owner-at-ratory animals, birds, and wildlife. (2) Terminal (ago- tended euthanasia. In overdose situations, these agentsnal) gasps that can occur in animals euthanized by IV can cause death; however, doses that consistently willbarbiturates are not seen with use of T-61. produce death have not been established for most spe- cies. In mice, injection of 100 µL of a 10:1 (mg:mg) Disadvantages—(1) T-61 is currently not being man- solution of ketamine:xylazine resulted in death withinufactured in the United States. (2) Slow IV injection is 3 to 5 seconds after completion of the injection.285 In-necessary to avoid dysphoria prior to unconsciousness. traperitoneal injection of dissociative agents in combi-(3) Each animal must be appropriately restrained and nation with α2-adrenergic receptor agonists at 5 timesthe agent must be administered by trained personnel. (4) the anesthetic dose has been used as a means of eutha-Secondary toxicosis may occur in animals that consume nizing laboratory animals.298remains of animals euthanized with T-61. (5) BecauseT-61 contains embutramide, a schedule III controlled Advantages—(1) These agents are readily available.drug, it is subject to the same restrictions in acquisition, (2) The combination of these agents causes rapid lossstorage, and use as other schedule III agents. of consciousness. (3) Although IV injection for eutha- nasia is preferred, these combinations can be delivered General recommendations—T-61 is acceptable as an IM in situations where IV administration is not feasibleagent of euthanasia provided it is administered appro- or is dangerous.priately by trained personnel. Routes of administrationof T-61 other than IV are not acceptable. Disadvantages—(1) These agents are not FDA ap- proved for use as agents of euthanasia. (2) Doses thatM2.7 ULTRAPOTENT OPIOIDS consistently produce rapid death have not been estab- Etorphine hydrochloride and carfentanil citrate lished for most drugs and species. (3) The cost of theare ultrapotent opioids (10,000 times as potent as mor- higher doses of agents required to cause death may sub-phine sulfate) that are FDA approved for the immobi- stantially exceed that of an approved euthanasia agent.lization of wildlife.296 These opioids have been used as (4) Many dissociative agents are controlled substancesimmobilization and extralabel euthanasia drugs pri- and their acquisition, storage, and use are restricted. (5)marily for large animals, particularly wildlife. Carfen- Some injectable agents can be hazardous for human per-tanil has been used transmucosally in a lollipop form sonnel if accidental exposure occurs. (6) The environ-to euthanize captive large apes.297 These drugs act on mental impact of residues of injectable anesthetics in theµ opioid receptors to cause profound CNS depression, remains of euthanized animals has not been determined.with death secondary to respiratory arrest. General recommendations—In species for which Advantages—(1) Etorphine and carfentanil can be effective euthanasia doses and routes have been estab-delivered IM or transmucosally in situations where IV lished, overdose of dissociative agent–α-2-adrenergicadministration is unfeasible or dangerous. (2) These combinations is an acceptable method of euthanasia.drugs have a rapid onset of action. These agents are acceptable with conditions in situa- tions where approved euthanasia drugs are not avail- Disadvantages—(1) These drugs are strictly regulat- able or as secondary means of euthanasia in alreadyed, require special licensing to obtain and use, and are not anesthetized animals provided utmost care is taken toFDA approved for use as agents of euthanasia. (2) There is ensure that death has occurred prior to disposing of an-substantial risk for humans handling the drugs, which can imal remains. These combinations are also acceptablebe absorbed through broken skin or mucous membranes. as the first step in a 2-step euthanasia method. Until the(3) These opioids may pose a risk of secondary toxicosis if environmental impact of tissue residues is determined,the remains of euthanized animals are ingested; therefore special care must be taken in the disposal of animal re-proper disposal of animal remains is essential. mains. Injectable anesthetics should not be used in ani- mals intended for consumption. General recommendations—Etorphine or carfent-anil is acceptable with conditions for euthanasia only M2.9 POTASSIUM CHLORIDEin situations where use of other euthanasia methods is AND MAGNESIUM SALTSimpractical or dangerous. Personnel handling the drugs Although unacceptable when used in consciousmust be familiar with their hazards, and a second per- vertebrate animals, a solution of potassium chloride,son should be standing by and be prepared to summon magnesium chloride, or magnesium sulfate injected IVmedical support and administer first aid in case of ac- or intracardially in an animal that is unconscious or un-cidental human exposure. der general anesthesia is an acceptable way to induce30 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 31. cardiac arrest and death. The potassium ion is cardio- sium sulfate and sodium pentobarbital as an economi-toxic, and rapid IV or intracardiac administration of 1 cal anesthesia and euthanasia agent for large animals,to 2 mmol/kg (0.5 to 0.9 mmol/lb) of body weight (1 but now is rarely used for this application in veterinaryto 2 mEq K+/kg; 75 to 150 mg/kg [34.1 to 68.2 mg/lb] medicine. α Chloralose is a longer-acting derivative ofof potassium chloride) will cause cardiac arrest.299 This chloral hydrate that has been used for anesthesia ofis an injectable technique for euthanasia of livestock or laboratory animals, particularly for study of cerebro-wildlife species that may reduce the risk of toxicosis for vasculature.303,304 When administered IV, these agentspredators or scavengers in situations where the remains have almost immediate sedative action, but unlessof euthanized animals may be consumed.300,301 Potassi- combined with other anesthetics, the onset of anesthe-um chloride injected IV at 3 mEq/kg (1.4 mEq/lb) into sia is delayed. Death is caused by hypoxemia resultingparrots anesthetized with isoflurane caused mild vocal- from progressive depression of the respiratory center,ization in 1 of 6 birds and resulted in asystole in 68 and may be preceded by gasping, muscle spasms, andseconds.302 Use of 10 mEq/kg (4.5 mEq/lb) IV in anes- vocalization.thetized parrots resulted in involuntary muscle tremorsin 5 of 6 birds and caused asystole in 32.8 seconds. Nei- Advantages—(1) Historically, chloral hydrate wasther dosage resulted in histologic artifacts. an inexpensive anesthetic and euthanasia agent, mak- Magnesium salts may also be mixed in water for ing it economical for large animals. (2) Schedule IV sta-use as immersion euthanasia agents for some aquatic tus makes chloral hydrate somewhat simpler to obtain,invertebrates. In these animals, magnesium salts induce store, and administer than schedule II or III drugs, suchdeath through suppression of neural activity.134 as sodium pentobarbital. Advantages—(1) Potassium chloride and magne- Disadvantages—(1) Chloral hydrate depresses thesium salts are not controlled substances and are easily cerebrum slowly; therefore, restraint may be a prob-acquired, transported, and mixed in the field. (2) Po- lem for some animals. (2) Chloral hydrate is no lon-tassium chloride and magnesium salt solutions, when ger available as an FDA-approved drug in the Unitedadministered after rendering an animal unconscious, States, so it must be compounded from bulk drug. Thisresult in animal remains that are potentially less toxic is problematic because of the lack of manufacturingfor scavengers and predators and may be a good choice controls, tests for potency, and illegality of compound-in cases where proper disposal of animal remains (eg, ing from bulk drugs.rendering, incineration) is impossible or impractical. General recommendations—Chloral hydrate and α Disadvantages—(1) Rippling of muscle tissue and chloralose are not acceptable euthanasia agents becauseclonic spasms may occur upon or shortly after injec- the associated adverse effects may be severe, reactionstion. (2) Potassium chloride and magnesium salt solu- can be aesthetically objectionable, and other productstions are not approved by the FDA for use as euthanasia are better choices.agents. (3) Saturated solutions are required to obtainsuitable concentrations for rapid injection into large M2.11 ALCOHOLSanimals. Ethanol and other alcohols increase cell membrane fluidity, alter ion channels within neural cells, and General recommendations—Personnel performing decrease nerve cell activity.305 Alcohols induce deaththis technique must be trained and knowledgeable in through nervous system and respiratory depression, re-anesthetic techniques, and be competent in assessing sulting in anesthesia and anoxia. Alcohols have beenthe level of unconsciousness that is required for ad- used as secondary euthanasia methods for some finfishministration of potassium chloride and magnesium species306 and as primary injectable euthanasia agents insalt solutions IV. Administration of potassium chloride mice used for antibody production.307 In the latter, miceor magnesium salt solutions IV requires animals to be receiving IP injections of 0.5 mL of 70% ethanol devel-in a surgical plane of anesthesia characterized by loss oped gradual loss of muscle control, coma, and deathof consciousness, loss of reflex muscle response, and within 2 to 4 minutes. This method has been proposedloss of response to noxious stimuli. Use in unconscious as a potential alternative to barbiturate euthanasia inanimals (made recumbent and unresponsive to noxious mice being used for antibody production, especially “instimuli) is acceptable in situations where other eutha- developing countries involved in vaccine development,nasia methods are unavailable or not feasible. Although antibody production and subsequent serological analy-no scavenger toxicoses have been reported with potas- sis.”307 Tribromoethanol is used as an anesthetic agentsium chloride or magnesium salts in combination with in laboratory rodents.a general anesthetic, proper disposal of animal remainsshould always be attempted to prevent possible toxi- Advantages—(1) Alcohol is inexpensive and read-cosis by consumption of animal remains contaminated ily available.with general anesthetics. Disadvantages—(1) Alcohols produce dose-relatedM2.10 CHLORAL HYDRATE irritation to tissue. (2) Onset of insensibility and deathAND α CHLORALOSE can be delayed following alcohol administration. (3) Chloral hydrate (1,1,1-trichloro-2,2,-dihydroxy- The volume required to euthanize animals larger thanethane) was once used in combination with magne- mice renders most alcohols impractical as euthanasiaAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 31
  • 32. agents. (4) Alcohols are not FDA approved as eutha- lb]) did not result in euthanasia, with 6 of 20 frogs re-nasia agents. (5) Tribromoethanol is not commercially gaining mobility within 3 hours after injections. Con-available as a pharmaceutical-grade product and must sequently, intracoelomic injection of MS 222 is not con-be compounded. sidered to be an acceptable method of euthanasia for X laevis and possibly other amphibians. General recommendations—Ethanol in low concen- A 2-stage euthanasia method for reptiles using MStrations is an acceptable secondary means of euthanasia 222 has been described.293 The first stage entails intra-in finfish rendered insensible by other means and as a coelomic injection of 250 to 500 mg/kg (113.6 to 227.3primary or secondary means of euthanasia of some in- mg/lb) of a pH-neutralized solution (0.7% to 1.0% MSvertebrates. Immersion in high concentrations (eg, 70%) 222), which results in rapid loss of consciousness (< 30of ethanol is not acceptable. Ethanol may be acceptable seconds to 4 minutes). Once unconsciousness occurs,with conditions as an agent of euthanasia for mice in a second intracoelomic injection of unbuffered 50% MSspecific situations, but is unacceptable as an agent of eu- 222 is administered.thanasia for larger species. Tribromoethanol is acceptablewith conditions as a method for euthanasia of laboratory Advantages—(1) MS 222 is soluble in both freshrodents when approved by the IACUC and prepared, and salt water and can be used for a wide variety ofstored, and administered at the appropriate dosage. finfish, amphibians, and reptiles. (2) MS 222 is com- mercially available and is not a controlled substance,M2.12 TRICAINE which increases ease of acquisition, storage, and ad-METHANESULFONATE (MS 222, TMS) ministration. Tricaine methanesulfonate, commonly referred toas MS 222, is an anesthetic agent that is FDA approved Disadvantages—(1) MS 222 is expensive and may be(Finquel and Tricaine-S only) for temporary immobili- cost prohibitive for use for large finfish, amphibians, andzation of finfish, amphibians, and other aquatic, cold- reptiles or for large populations. (2) There appears to beblooded animals.308 Tricaine methanesulfonate has been substantial species variability in response to MS 222, withused for euthanasia of reptiles, amphibians, and finfish. some species requiring higher doses or secondary mea-Tricaine is a benzoic acid derivative and, in water of low sures to ensure death. (3) Injection of MS 222 is not ap-alkalinity (< 50 mg/L as CaCO3), the solution should propriate for finfish as rapid excretion via the gills rendersbe buffered with sodium bicarbonate.309 A 10 g/L stock it ineffective by this route.309 (4) MS 222 cannot be usedsolution can be made, and sodium bicarbonate added to in animals intended for human consumption. (5) Occupa-saturation, resulting in a pH between 7.0 and 7.5 for the tional exposure to MS 222 has been associated with retinalsolution. The stock solution should be protected from toxicity in humans.313 (6) MS 222 is not FDA approvedlight and refrigerated or frozen if possible. The solution for use as an agent of euthanasia. (7) The impact of MSshould be replaced monthly and any time a brown color 222 residues in euthanized finfish on the environment oris observed.310 Potency is increased in warm water and scavenger species has not been determined.decreased in cold water.309 Immersion of finfish in solu-tions of MS 222 for 10 minutes following loss of rhyth- General recommendations—MS 222 is an acceptablemic opercular movement is sufficient for euthanasia method of euthanasia for finfish and for some amphib-of most finfish. Due to species differences in response ians and reptiles. When used for large finfish and someto MS 222, a secondary method of euthanasia is rec- amphibians (eg, Xenopus spp), a secondary methodommended in some finfish and amphibians to ensure should be used to ensure death. By itself, intracoelo-death.309,311 In the United States, there is a 21-day with- mic injection of MS 222 is not an acceptable euthana-drawal time for MS 222; therefore, it is not appropriate sia method for X laevis and possibly other amphibians.for euthanasia of animals intended for consumption. Animals euthanized with MS 222 should not be used as MS 222 rapidly enters the CNS and alters nerve food sources for humans or other animals.conduction through blockade of voltage-sensitive so-dium channels.311 Additionally, accumulation within M2.13 BENZOCAINE HYDROCHLORIDEventricular myocardium results in decreased cardiovas- Benzocaine base, a compound similar to tricainecular function. Death is due to decreased nervous and methanesulfonate, is not water soluble and therefore iscardiovascular function. prepared as a stock solution (100 g/L) with acetone or Studies312 with Xenopus laevis (African clawed frog ethanol; the presence of these solvents can be irritat-or platanna) have shown that the concentrations of MS ing to tissues. Conversely, benzocaine hydrochloride is222 traditionally used for amphibian euthanasia (0.25 water soluble and can be used directly for either an-to 0.5 g/L) are not sufficient to induce reliable eutha- esthesia or euthanasia of finfish and amphibians.293,310nasia in this species. Immersion of frogs in 5 g/L of MS Benzocaine-containing products should be protected222 resulted in deep anesthesia within 4 minutes, but at from light and protected from freezing or excessiveleast 1 hour of immersion at this concentration was re- heat (> 40°C). Topical application of 7.5% or 20% ben-quired to reliably euthanize 100% of frogs. The authors zocaine hydrochloride gel on an amphibian’s ventrumof that study recommended that if a concentration of is effective and does not require buffering. Similarly toMS 222 < 5 g/L or a shorter time frame than 1 hour MS 222, benzocaine acts through blockade of voltage-is allowed, a secondary euthanasia method should be sensitive sodium channels within the CNS and heart,used for X laevis. Intracoelomic injection of MS 222 at resulting in depression of the nervous and cardiovas-the highest possible dosage (2,590 mg/kg [1,177 mg/ cular systems.32 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 33. The application of benzocaine hydrochloride gel induction, prolonged recovery, and narrow margin ofto the ventral abdomen of amphibians (20% concentra- safety, as it can cause rapid onset of ventilatory failure attion; 2.0-cm X 1.0-mm application) is an effective means high concentrations (> 400 mg/L).321of anesthesia and euthanasia for some species.312,314,315 The anesthetic mechanism of clove oil and its de-Following application of the gel to the ventrum of X rivatives has been poorly studied, but they appear tolaevis and placement in a wet bucket, righting and with- act similarly to other local anesthetics by inhibition ofdrawal reflexes subsided within 7 minutes, and death voltage-sensitive sodium channels within the nervousoccurred within 5 hours.312 No evidence of dermal in- system.296 Studies322–324 of rodents indicate this class ofjury, loss of dermal hydration, or difficulty breathing agents may cause paralysis in addition to their anes-was associated with topical application of benzocaine thetic effects.hydrochloride gel to amphibians. A recent investigationon euthanasia of adult X laevis describes a dose of 182 Advantages—(1) Clove oil and its derivatives aremg/kg (82.7 mg/lb) of benzocaine hydrochloride gel as widely available, are relatively inexpensive, and are noteffective.312 A comparison of benzocaine hydrochloride controlled substances. (2) These agents have a short in-application with ice-slurry immersion for euthanasia of duction time. (3) Clove oil and its derivatives are effec-bony bream (Nematalosa erebi) indicated that, for cer- tive at a wide range of water temperatures.tain warm water finfish species, an ice-slurry elicits lessmotor response than benzocaine overdose as a method Disadvantages—(1) Clove oil and its derivatives areof euthanasia, but additional work is needed to deter- not FDA approved for use as an agent of euthanasia.mine the most humane method.316 (2) Animals euthanized with clove oil products are not approved for human consumption. (3) Some clove oil Advantages—(1) Benzocaine hydrochloride is a derivatives are potential carcinogens. (4) The impact ofrelatively fast-acting and effective euthanasia agent for clove oil residues in euthanized finfish on the environ-finfish and amphibians. (2) Benzocaine hydrochloride ment or scavenger species has not been determined.is not a controlled substance. (3) Benzocaine hydro-chloride has low toxicity for humans at concentrations General recommendations—Clove oil, isoeugenol,used to euthanize finfish. (4) Benzocaine hydrochloride and eugenol are acceptable agents of euthanasia forposes little environmental risk as it is readily filtered finfish. It is recommended that, whenever possible,by use of activated carbon and breaks down in water products with standardized, known concentrations ofwithin approximately 4 hours. essential oils be used so that accurate dosing can occur. These agents are not acceptable means of euthanasia for Disadvantages—(1) Benzocaine hydrochloride is animals intended for consumption.not FDA approved for use as an agent of euthanasia.(2) Benzocaine hydrochloride may be cost prohibitive M2.15 2-PHENOXYETHANOLfor euthanasia of larger finfish, amphibians, and reptiles Immersion in 2-phenoxyethanol has been usedor large populations. (3) Benzocaine hydrochloride so- for anesthesia and euthanasia of finfish at concentra-lutions must be carefully buffered to avoid tissue irrita- tions of 0.3 to 0.5 mg/L or higher.309 The solubilitytion. (4) The impact of benzocaine residues in eutha- of 2-phenoxyethanol is reduced in colder water. Thenized finfish on the environment or scavenger species mechanism of action of 2-phenoxyethanol is poorly un-has not been determined. derstood, but death is thought to occur from hypoxia secondary to CNS depression. Finfish should be kept in General recommendations—Benzocaine hydro- the 2-phenoxyethanol solution for at least 10 minuteschloride gel and solutions are acceptable agents for after cessation of opercular movement.euthanasia for finfish and amphibians. Benzocaine hy-drochloride is not an acceptable euthanasia agent for Advantages—(1) 2-phenoxyethanol can be used inanimals intended for consumption. a 1-step immersion method for euthanasia of finfish. (2) 2-phenoxyethanol is not a controlled substance.M2.14 CLOVE OIL, ISOEUGENOL, AND EUGENOL Cloves contain a number of essential oils, includ- Disadvantages—(1) Induction times can be prolonged.ing eugenol, isoeugenol, and methyleugenol.317 Eugenol (2) There are species variations in dosage levels and dura-comprises 85% to 95% of the essential oils in cloves, and tion of exposure required for euthanasia. (3) Some spe-has been used as a food flavoring and a local anesthetic cies exhibit hyperactivity prior to loss of consciousness.for human dentistry. It is also classified as an exempted (4) 2-phenoxyethanol is not FDA approved for use as anminimum-risk pesticide active ingredient by the US EPA. agent of euthanasia. (5) The impact of 2-phenoxyethanolEugenol exhibits antifungal, antibacterial, antioxidant, residues in euthanized finfish on the environment or scav-and anticonvulsant activity. Some other components of enger species has not been determined.clove oil, such as isoeugenol, are equivocal carcinogensbased on studies in rodents.318 Clove oil and its extracts General recommendations—Although there arehave become popular as anesthetic agents for freshwater probably more efficient immersion agents available,and marine finfish because of their wide availability, low 2-phenoxyethanol is an acceptable method of euthana-cost, and shorter induction times when compared with sia for finfish under certain circumstances. 2-phenoxy-MS 222.319,320 When compared with MS 222 as an anes- ethanol is not an acceptable means of euthanasia in ani-thetic agent, eugenol was found to have a more rapid mals intended for consumption.AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 33
  • 34. M2.16 QUINALDINE (2-METHYLQUINOLINE, lutions are corrosive and pose risk of dermal, ocular,QUINALIDINE SULFATE) and respiratory injury to personnel if mishandled. (2) Quinaldine has low solubility in water and there- Sodium hypoclorite is not FDA approved for euthana-fore must first be dissolved in acetone or alcohol and sia.then buffered with bicarbonate.309 The potency of quin-aldine varies with species, water temperature, water pH, General recommendations–When used on early em-and mineral content of water. Quinaldine acts through bryonic and larval stages prior to development of no-depression of sensory centers of the CNS. ciceptive abilities, application of hypochlorites can be an acceptable means of euthanasia. Hypochlorites are Advantages—(1) Quinaldine can be used in a unacceptable as the sole means of euthanasia of organ-1-step immersion method for euthanasia of finfish. (2) isms beyond these embryonic and larval stages. Use ofQuinaldine is not a controlled substance. hypochlorites is unnacceptable for finfish intended for human consumption. Disadvantages—(1) Quinaldine is not FDA ap-proved for use as an agent of euthanasia. (2) The im- M2.19 FORMALDEHYDEpact of quinaldine residues in euthanized finfish on the Formaldehyde causes cellular damage throughenvironment or scavenger species has not been deter- oxidative injury as well as through formation of cross-mined. linkages with DNA, RNA, and proteins.328 Formalde- hyde can be used to euthanize and preserve Porifera General recommendations—Quinaldine is an ac- (sponges) as these invertebrates lack nervous tissue.ceptable method of euthanasia for finfish under certaincircumstances. Quinaldine is not an acceptable means Advantages—(1) Formaldehyde is inexpensive,of euthanasia in animals intended for consumption. easily obtainable, and not a controlled substance. (2) Formaldehyde rapidly fixes tissues, preserving struc-M2.17 METOMIDATE ture for later study. Metomidate is a highly water-soluble, nonbarbi-turate hypnotic that acts by causing CNS depression. Disadvantages—(1) Formaldehyde poses sub-It is currently listed in the Index of Legally Marketed stantial health risks for personnel, including respira-Unapproved New Animal Drugs for Minor Species by tory, dermal, and ocular irritation and hypersensitivity.the FDA for use in sedation and anesthesia. While it is a Formaldehyde is also a known human carcinogen.329rapidly acting euthanasia compound for certain specieswhen used at 10 times the upper limit of the recom- General recommendations—Formaldehyde is anmended anesthetic dose, its listing in the Index makes acceptable method of euthanasia for Porifera species.extralabel use (eg, its use for euthanasia) illegal. Should Formaldehyde is acceptable as an adjunctive methodthe index status of metomidate change to inclue eutha- of euthanasia for Coelenterates (comb jellies, corals,nasia, or should FDA approval be obtained (thereby anemones) and Gastropod molluscs (snails, slugs) onlyallowing extralabel use under AMDUCA), metomidate after these animals have been rendered nonresponsivewould be considered an acceptable agent of euthanasia by other methods (eg, magnesium chloride330). Form-for some species of finfish under certain circumstances. aldehyde is unacceptable as a first step or adjunctive Metomidate is not an acceptable means of euthana- method of euthanasia for other animal species.sia in animals intended for consumption. M2.20 UNACCEPTABLE AGENTSM2.18 SODIUM HYPOCHLORITE Strychnine, nicotine, caffeine, cleaning agents, sol- Sodium hypochlorite (bleach) and solutions made vents, pesticides, disinfectants, and other toxicants notfrom calcium hypochlorite granules act as solvents and specifically designed for therapeutic or euthanasia useoxidants in tissue, resulting in saponification of fatty are unacceptable for use as euthanasia agents under anyacids, denaturation of proteins, and derangement of circumstances.cellular processes.326 Hypochlorite has been used to Magnesium sulfate, potassium chloride, and neu-euthanize unhatched and hatched zebrafish up to 7 romuscular blocking agents are unacceptable for usedays after fertilization, after which time hatchlings are as euthanasia agents in conscious vertebrate animals.considered developed beyond an embryonic form and These agents may be used for euthanasia of anesthe-capable of experiencing distress or pain.327 Hypochlo- tized or unconscious animals as previously described.rite has also been used to terminate embryos in variousresearch settings. M3. PHYSICAL METHODS Advantages—(1) Sodium hypochlorite and calciumhypochlorite are inexpensive, are readily available, and, M3.1 COMMON CONSIDERATIONSat the concentrations used for embryonic and larval Physical methods of euthanasia include captivestage destruction (1% to 10%), pose minimal hazards bolt, gunshot, cervical dislocation, decapitation, elec-to personnel. (2) These products are not controlled trocution, focused beam microwave irradiation, thorac-substances. ic compression, exsanguination, maceration, stunning, and pithing. When properly used by skilled personnel Disadvantages—(1) Concentrated hypochlorite so- with well-maintained equipment, physical methods of34 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 35. euthanasia may result in less fear and anxiety and be guns must be stored in a dry location because dampmore rapid, painless, humane, and practical than other cartridges will reduce effectiveness.336forms of euthanasia. Exsanguination, stunning, andpithing are not recommended as a sole means of eu- Advantages—(1) Both regular and air injectionthanasia, but may be considered as adjuncts to other penetrating captive bolts may be used effectively foragents or methods. euthanasia of animals in research facilities and on the Some consider physical methods of euthanasia aes- farm, when the use of drugs for this purpose is inap-thetically displeasing. There are occasions, however, propriate or impractical. (2) They do not chemicallywhen what is perceived as aesthetic and what is most contaminate tissues.humane are in conflict. Despite their aesthetic challeng-es, in certain situations physical methods may be the Disadvantages—(1) Euthanasia by captive bolt canmost appropriate choice for euthanasia and rapid relief be aesthetically displeasing. (2) Death may not occurof pain and suffering. Personnel using physical meth- if equipment is not maintained and used properly. (3)ods of euthanasia must be well trained and monitored The air injection captive bolt must never be used onfor each type of physical method performed to ensure ruminants that will be used for food because of con-euthanasia is conducted appropriately. They must also cerns about contamination of meat with specified riskbe sensitive to the aesthetic implications of the method materials (neurologic tissue). (4) Because the penetrat-and convey to onlookers what they should expect to ing captive bolt is destructive, brain tissue may not beobserve when at all possible. able to be examined for evidence of rabies infection or Since most physical methods involve trauma, there chronic wasting disease.is inherent risk for animals and people. If the methodis not performed correctly, personnel may be injured General recommendations—Use of the penetratingor the animal may not be effectively euthanized; per- captive bolt is acceptable with conditions and is a prac-sonnel skill and experience are essential. Inexperienced tical method of euthanasia for horses, ruminants, andpersons should be trained by experienced persons and swine. To ensure death, it is recommended that animalsshould practice on euthanized animals or anesthetized be immediately exsanguinated or pithed (see adjunc-animals to be euthanized until they are proficient in tive methods) unless a powerful captive bolt gun de-performing the method properly and humanely. After signed for euthanasia is used. These guns have recentlythe method has been applied, death must be confirmed become available and reduce the need to apply an ad-before disposal of the remains. junctive method. Ruminants used for food should not be pithed to avoid contamination of the carcass withM3.2 PENETRATING CAPTIVE BOLT specified risk materials. Captive bolt guns used for larg- Penetrating captive bolts have been used for eu- er species must have an extended bolt.thanasia of ruminants, horses, swine, laboratory rab-bits, and dogs.331 Their mode of action is concussion M3.3 NONPENETRATING CAPTIVE BOLTand trauma to the cerebral hemisphere and brain- The nonpenetrating captive bolt has a wide mush-stem.48,332,333 Adequate restraint is important to ensure room-shaped head that does not penetrate the brain ofproper placement of captive bolts. A cerebral hemi- large mammals, such as adult cattle, slaughter-weightsphere and the brainstem must be sufficiently disrupted pigs, sows, and adult sheep. In general, nonpenetratingby the projectile to induce sudden loss of consciousness captive bolt guns only stun animals and should not beand subsequent death. Appropriate placement of cap- used as a sole method of euthanasia. Correct position-tive bolts for various species has been described.130,332–335 ing is critical for an effective stun of an adult cow. Non-Signs of effective captive bolt penetration and death are penetrating captive bolts are not effective for stunningimmediate collapse and a several-second period of te- bulls, adult swine, or cattle with long hair.tanic spasm, followed by slow hind limb movements Purpose-built pneumatic nonpenetrating captiveof increasing frequency.46,47 The corneal reflex must be bolt guns have recently been developed and success-absent and the eyes must open into a wide blank stare fully used for euthanasia of suckling pigs,c neonatal ru-and not be rotated.45 minants,130 and turkeys.337 There are two types of penetrating captive bolts:a regular penetrating captive bolt and an air injection Advantage—Less damage to the brain.penetrating captive bolt. In both cases, the bolts pen-etrate the brain. In the air injection penetrating cap- Disadvantages—(1) Nonpenetrating captive bolttive bolt, air under high pressure is injected through guns only stun animals and therefore are generally notthe bolt into the brain to increase the extent of tissue effective as a sole means of euthanasia. The exception isdestruction. Powder-activated guns that use the tradi- nonpenetrating pneumatic captive bolt guns that havetional captive bolt are available in 9 mm, .22 caliber, been purpose-built for euthanasia of suckling pigs,c neo-and .25 caliber.130 Captive bolt guns powered by com- natal ruminants,130 and turkeys.338 (2) Depending on de-pressed air (pneumatic) are also available in regular and gree of destruction, use of a nonpenetrating captive boltair injection types. All captive bolt guns require careful may preclude postmortem diagnostics for diseases of themaintenance and cleaning after each day of use. Lack of brain, including rabies and chronic wasting disease.maintenance is a major cause of captive bolt gun failurefor both powder-activated and pneumatic captive bolt General recommendations—In general, nonpen-guns.101 Cartridges for powder-activated captive bolt etrating captive bolt guns should not be used as a soleAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 35
  • 36. method of euthanasia. However, pneumatic purpose- of euthanasia. Shooting should only be performed bybuilt nonpenetrating captive bolt guns have been used highly skilled personnel trained in the use of firearmssuccessfully to euthanize suckling pigs,c neonatal rumi- and only in jurisdictions that allow for legal firearmnants,130 and turkeys.339 use. The safety of personnel, the public, and other ani- mals that are nearby should be considered. The proce-M3.4 MANUALLY APPLIED dure should be performed outdoors and in areas whereBLUNT FORCE TRAUMA TO THE HEAD public access is restricted. Euthanasia by manually applied blunt force trauma In applying gunshot to the head as a method ofto the head must be evaluated in terms of the anatomic euthanasia for captive animals, the firearm should befeatures of the species on which it is to be performed, aimed so that the projectile enters the brain, causingthe skill of those performing it, the number of animals instant loss of consciousness.166,335,342–345 This must taketo be euthanized, and the environment in which it is into account differences in brain position and skullto be conducted. Manually applied blunt force trauma conformation between species, as well as the energy re-to the head can be a humane method of euthanasia for quirement for penetration of the skull and sinus.332,343neonatal animals with thin craniums if a single sharp Accurate targeting for a gunshot to the head in vari-blow delivered to the central skull bones with sufficient ous species has been described.343,344,346 For wildlife andforce can produce immediate depression of the CNS and other freely roaming animals, the preferred target areadestruction of brain tissue. When properly performed, should be the head. It may, however, not be possible orloss of consciousness is rapid. Personnel performing appropriate to target the head when killing is attemptedmanually applied blunt force trauma to the head must from large distances (missed shots may result in jawbe properly trained and monitored for proficiency with fractures or other nonfatal injuries) or when diagnos-this method of euthanasia, and they must be aware of tic samples of brain tissue are needed for diagnosis ofits aesthetic implications. diseases (eg, rabies, chronic wasting disease) important Manually applied blunt force trauma to the head to public health. The appropriate firearm should be se-has been used primarily to euthanize small laboratory lected for the situation, with the goal being penetrationanimals with thin craniums.334,340,341 It has also been ap- and destruction of brain tissue without emergence fromplied for euthanasia of young piglets. The anatomic fea- the contralateral side of the head.130,347 A gunshot to thetures of neonatal calves make manually applied blunt heart or neck does not immediately render animals un-force trauma to the head unacceptable as a method of conscious, but may be required when it is not possibleeuthanasia for this species. to meet the POE’s definition of euthanasia.348 Personnel who have to perform manually appliedblunt force trauma to the head often find it displeas- M3.5.1 Basic Principles of Firearmsing and soon become fatigued. Fatigue can lead to in- To determine whether a firearm or type of ammuni-consistency in application, creating humane concerns tion is appropriate for euthanizing animals, some basicabout its efficacious application to large numbers of principles must be understood. The kinetic energy ofanimals. For this reason, the AVMA encourages those an object increases as the speed and weight or mass ofusing manually applied blunt force trauma to the head the object increase. In reference to firearms, the bullet’sas a euthanasia method to actively search for alternate kinetic energy (muzzle energy) is the energy of a bul-approaches. let as it leaves the end of the barrel when the firearm is discharged. Muzzle energy is frequently used as an Advantages—(1) Blunt force trauma applied man- indicator of a bullet’s destructive potential. The heavi-ually to the head is inexpensive and effective when er the bullet and the greater its velocity, the higher itsperformed correctly. (2) Blunt force trauma does not muzzle energy and capacity for destruction of objectschemically contaminate tissues. in its path. Muzzle energy (E) can be expressed as the mass of Disadvantages—(1) Manually applied blunt force the bullet (M) times its velocity (V) squared, divided bytrauma is displeasing for personnel who have to per- 2.349 However, to accommodate units of measure com-form it. (2) Repeatedly performing manually applied monly used in the United States for civilian firearms,blunt force trauma can result in personnel fatigue, loss energy (E) is expressed in foot-pounds. This is calcu-of efficacy, and humane concerns. (3) Trauma to the lated by multiplication of the bullet’s weight (W) timescranium can damage tissues and interfere with diagno- its velocity in feet per second (V) squared, divided bysis of brain diseases. 450,450. The International System of Units expresses muzzle energy in joules (J). General recommendations—Replace, as much as Representative ballistics data for various types ofpossible, manually applied blunt force trauma to the firearms are provided in Table 1. The muzzle energyhead with alternate methods. Manually applied blunt of commercially available ammunition varies greatly.force trauma is not acceptable for neonatal calves, be- For example, the difference in muzzle energy gener-cause of their anatomic features. ated from a .357 Magnum handgun loaded with a 180 grain compared with a 110 grain bullet may differ by asM3.5 GUNSHOT much as 180 foot-pounds.349 Velocity has an even great- A properly placed gunshot can cause immediate er impact on bullet energy than bullet mass. Selectioninsensibility and a humane death. Under some con- of an appropriate bullet and firearm is critical to goodditions, a gunshot may be the only practical method performance when conducting euthanasia procedures.36 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 37. Table 1—Average muzzle energies for common handguns and with rifles, the longer the barrel, the higher the muzzlerifles. (Adapted from USDA, 2004, National Animal Health Emer- velocity. Therefore, if a .22 is used for euthanasia it isgency Management System Guidelines, USDA, Washington, DC.Available at: www.dem.ri.gov/topics/erp/nahems_euthanasia.pdf best fired from a rifle. The .22 should never be used on[Accessed August 27 2009] and cited by Woods J, Shearer JK, , aged bulls, boars, or rams.351Hill J. Recommended on-farm euthanasia practices. In: GrandinT, ed. Improving animal welfare: a practical approach. Wallingford,Oxfordshire, England: CABI Publishing, 2010; 194–195.) M3.5.3 Bullet Selection While much of the emphasis in euthanasia by gun- Muzzle energy shot is placed on choice of the most appropriate firearm, Cartridge/firearm In foot pounds In joules it should be remembered that the gun is only the means of delivery. Bullet selection is quite possibly the most Handguns .40 Smith and Wesson 408 553 important consideration for euthanasia of livestock by .45 Automatic Colt Pistol 411 557 gunshot. There are three basic types of bullets pertinent .357 Magnum 557 755 to this discussion: solid points, hollow points, and full .41 Remington Magnum 607 823 10-mm Automatic 649 880 metal jacketed bullets. Solid-point bullets are preferred .44 Remington Magnum 729 988 for euthanasia since they are designed for greater pen- etration of their targets. Under ideal conditions this Rifles .223 Remington 1,296 1,757 type of bullet will also undergo moderate expansion to 30-30 Winchester 1,902 2,579 a mushroom shape that increases its destructive char- .308 2,648 3,590 acteristics. Hollow-point bullets are designed with a 30-06 Springfield 2,841 3,852 hollowed-out tip that causes rapid expansion and frag- mentation of the bullet on impact. The hollow-pointLighter-weight, higher-velocity bullets can have high design allows maximum transfer of energy without riskmuzzle energy, but decreased penetration, which can of overpenetration. For applications where it may bebe an issue when penetrating thick bones. desirable to control or reduce the degree of bullet pen- Whereas most euthanasia using firearms is con- etration, hollow-point bullets are preferred. However,ducted at close range, calculations of muzzle energy are for the purposes of euthanasia of livestock the first re-useful for determining which firearms are appropriate quirement is that the bullet possesses sufficient energyfor euthanasia of animals of varying sizes. As the bul- to penetrate the skull and enter the underlying brainlet travels beyond the muzzle of the firearm its energy tissue. The concern with hollow-point bullets is that,gradually begins to decrease. While this is not a con- since the majority of their energy is released on impactcern for the use of firearms in close proximity to the through fragmentation, they may not have sufficientanimal, when attempting to euthanize an animal from energy to traverse the skull. The other extreme is repre-a distance, to ensure accuracy and that an acceptable sented by full metal jacket bullets, which do not expandlevel of muzzle energy is achieved, a high-powered rifle or fragment on impact with their targets. These bulletsmay be the better choice for conducting euthanasia. In have a lead core with a thin metal jacket cover thatall cases, the most important factors in ensuring suc- completely covers (surrounds) the bullet. Full metalcessful euthanasia are the experience and skill of the jacket bullets generally achieve maximum penetration,shooter. which may have benefits for euthanasia but also cre- ates additional safety hazards for bystanders. ShotgunsM3.5.2 Muzzle Energy Requirements loaded with shot shells (number 4, 5, or 6) have suf- For euthanasia, the combination of firearm and ficient energy to traverse the skull but, unlike the pos-ammunition350 selected must achieve a muzzle energy sibility of bullets from either a handgun or rifle, rarelyof at least 300 ft-lb (407 J) for animals weighing up to exit the skull. These are important considerations when400 lb (180 kg). For animals larger than 400 lb, 1,000 selecting a firearm for on-farm euthanasia. Probably theft-lb (1,356 J) is required.130 As demonstrated by Table most important point to be made relative to the use of1, handguns do not typically achieve the muzzle en- gunshot for euthanasia is that scientific information onergy required to euthanize animals weighing more than firearm and bullet selection is lacking. This is an area of400 lb (180 kg), and therefore rifles must be used to urgent need in euthanasia research.euthanize these animals. Some would argue that the muzzle energies recom- M3.5.4 Firearm Safetymended are well beyond what is necessary to achieve Firearm safety cannot be overemphasized. Gunssatisfactory results. Anecdotal comment suggests that are inherently dangerous and must be handled withthe .22 LR is one of the most frequently used firearms caution at all times. This needs to become the mindsetfor euthanasia of livestock with varying degrees of suc- in handling and use of firearms. Common recommen-cess. There is little doubt that success or failure is par- dations include the following: (1) assume that all fire-tially related to firearm and bullet characteristics, but arms are loaded, (2) always know where the muzzle isprobably more so to selection of the ideal anatomic site and never allow it to point in the direction of oneself or(ie, a site more likely to affect the brainstem) for con- bystanders, (3) keep fingers away from the trigger andducting the procedure. The Humane Slaughter Associa- out of the trigger guard until ready to fire, (4) be suretion lists multiple firearms for euthanasia of livestock, of the target and what lies beyond it, and (5) always beincluding shotguns (12, 16, 20, 28, and .410 gauges), sure that the gun is unloaded when not in use. Readershandguns (.32 to .45 caliber), and rifles (.22, .243, desiring more information or training on proper use of.270, and .308). In general, when comparing handguns firearms are advised to contact local hunter safety pro-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 37
  • 38. grams. These programs offer training in firearm safety and the neck is hyperextended and dorsally twisted toand also provide information on rules and regulations separate the first cervical vertebra from the skull.334,353for firearm use. For poultry and other birds, the legs of the bird should Firearms should never be held flush to an animal’s be grasped (or wings if grasped at the base) and thebody. The pressure within the barrel when fired may neck stretched by pulling on the head while applyingcause the barrel of the gun to explode, placing the a ventrodorsal rotational force to the skull. Crushingshooter and observers at great risk of injury. Ideally, the of cervical vertebrae and spinal cord is not acceptablemuzzle of the firearm should be held within 1 to 2 feet unless the bird is first rendered unconscious. Personnelof the animal’s forehead and perpendicular to the skull should be trained on anesthetized and/or dead animalswith the intended path of the bullet roughly in the di- to demonstrate proficiency.rection of the foramen magnum. This will reduce the Data suggest that electrical activity in the brainpotential for ricochet while directing the bullet toward persists for 13 seconds following cervical dislocationthe cerebrum, midbrain, and medulla oblongata, which in rats,58 and unlike decapitation, rapid exsanguina-will assure immediate loss of consciousness and rapid tion does not contribute to loss of consciousness.56,57death. For some classes of poultry there is evidence that cervi- cal dislocation may not cause immediate unconscious- Advantages—(1) Loss of consciousness is instanta- ness.337–339,354neous if the projectile destroys most of the brain. (2)Given the need to minimize stress induced by handling Advantages—(1) Cervical dislocation is a methodand human contact, gunshot may be the most practi- that may induce rapid loss of consciousness.58,275 (2) Itcal and logical method of euthanasia for wild or free- does not chemically contaminate tissue. (3) It is rapidlyranging species. accomplished. Disadvantages—(1) Gunshot may be dangerous for Disadvantages—(1) Cervical dislocation may bepersonnel. (2) It is aesthetically unpleasant for many. aesthetically displeasing to personnel performing or(3) Under field conditions, it may be difficult to hit observing the method. (2) Cervical dislocation requiresthe vital target area. (4) Brain tissue may not be able mastering technical skills to ensure loss of conscious-to be examined for evidence of brain diseases (eg, ra- ness is rapidly induced. (3) Its use for euthanasia is lim-bies infection, chronic wasting disease) when the head ited to small birds, poultry, mice, immature rats (< 200is targeted. (5) Skill in application of firearms and spe- g), and rabbits.cies-specific knowledge of appropriate target sites is re-quired. In some states, firearm use is not permitted if General recommendations—Manual cervical dislo-the operator has been convicted of a felony. cation is acceptable with conditions for euthanasia of small birds, poultry, mice, rats weighing < 200 g, and General recommendations—When other methods rabbits when performed by individuals with a demon-cannot be used, an accurately delivered gunshot is ac- strated high degree of technical proficiency. In lieu ofceptable with conditions for euthanasia.344,352 When an demonstrated technical competency, animals must beanimal can be appropriately restrained, the penetrating unconscious or anesthetized prior to cervical disloca-captive bolt, preferably one designed for euthanasia, is tion. For heavy rats and rabbits, the large muscle masspreferred to a gunshot because it is safer for personnel. in the cervical region makes manual cervical disloca-Prior to shooting, animals accustomed to the presence tion physically more difficult.355 When performed onof humans should be treated in a calm and reassuring poultry, cervical dislocation must result in luxationmanner to minimize anxiety. In the case of wild animals, of the cervical vertebrae without primary crushing ofgunshots should be delivered with the least amount of the vertebrae and spinal cord. In some classes of poul-prior human contact necessary. Gunshot should not be try, there is evidence that cervical dislocation may notused for routine euthanasia of animals in animal con- cause immediate unconsciousness.337–339,354 In these cas-trol situations, such as municipal pounds or shelters. es, other physical methods such as blunt force trauma or decapitation may be more humane356 and should beM3.6 CERVICAL DISLOCATION employed when available or practicable. Cervical dislocation has been used for many years Those responsible for the use of this method mustfor euthanasia and, when performed by well-trained ensure that personnel performing cervical dislocationindividuals on appropriate animals, appears to be hu- have been properly trained and consistently apply itmane. However, there are few scientific studies avail- humanely and effectively.able to confirm this observation. The method has beenused to euthanize small birds, poultry, mice, immature M3.7 DECAPITATIONrats (< 200 g [7.1 oz]), and rabbits. For mice and rats, Decapitation can be used to euthanize rodents andthe thumb and index finger are placed on either side of small rabbits in research settings. It provides a meansthe neck at the base of the skull or, alternatively, a rod to recover tissues and body fluids that are chemicallyis pressed at the base of the skull. With the other hand, uncontaminated. It also provides a means of obtainingthe base of the tail or the hind limbs are quickly pulled, anatomically undamaged brain tissue for study.357causing separation of the cervical vertebrae from the Although it has been demonstrated that electricalskull. For immature rabbits, the head is held in 1 hand activity in the brain persists for 13 to 14 seconds follow-and the hind limbs in the other. The animal is stretched ing decapitation,59 more recent studies and reports56–5838 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 39. indicate this activity does not imply that pain is per- the seizure are extension of the limbs, opisthotonus,ceived, and in fact conclude that loss of consciousness downward rotation of the eyeballs, and a tonic (rigid)develops rapidly. Visually evoked potentials in mice spasm changing to a clonic (paddling) spasm withwere reduced more quickly after cervical dislocation eventual muscle flaccidity.compared with decapitation.51 There are three approaches to the use of electricity Guillotines designed to accomplish decapitation of for euthanasia. They are head only, 1-step head to body,adult rodents and small rabbits in a uniformly instan- and 2-step head and body. To be effective for euthana-taneous manner are commercially available. Guillotines sia all three of these methods must induce a grand malare not commercially available for neonatal rodents, but epileptic seizure.sharp blades can be used for this purpose. For the head-only procedure, an electrical current is passed through the head to induce a seizure. This Advantages—(1) Decapitation appears to induce causes a temporary loss of consciousness of 15 to 30rapid loss of consciousness.56–58 (2) It does not chemi- seconds’ duration,106,372,373 but does not induce cardiaccally contaminate tissues. (3) It is rapidly accomplished. fibrillation. For this reason, head-only application must be immediately followed by a secondary procedure to Disadvantages—(1) Handling and restraint re- cause death. When the head-only procedure is applied,quired to perform decapitation may be distressful for the grand mal seizure is easily observable. Electricallyanimals.358 (2) The interpretation of the presence of induced cardiac fibrillation, exsanguination, or otherelectrical activity in the brain following decapitation appropriate adjunctive methods may be used to achievehas created controversy, and its importance may still death and should be performed within 15 seconds ofbe open to debate.56–59 (3) Personnel performing this when the animal becomes unconscious.method should recognize the inherent danger of the In the 1-step head-to-body approach an electricalguillotine and take precautions to prevent personal in- current is simultaneously passed through both the brainjury. (4) Decapitation may be aesthetically displeasing and the heart. This simultaneously induces a grand malto personnel performing or observing the method. seizure and electrocutes the animal by inducing cardiac arrest.106,359,374–376 Because electricity passes through the General recommendations—This method is accept- spinal column, clinical signs of the grand mal seizureable with conditions if performed correctly, and it may may be masked; however, it is usually possible to see abe used in research settings when its use is required weak tonic phase and weak clonic phase after a 3-sec-by the experimental design and approved by the IA- ond application. If current is applied for more than 3CUC. Decapitation is justified for studies where un- seconds, tonic and clonic spasms may be blocked. Thedamaged and uncontaminated brain tissue is required. 1-step approach must be used with amperage settingsThe equipment used to perform decapitation must be that have been scientifically verified to induce a seizure.maintained in good working order and serviced on a Recommended amperages are 1.25 amps for pigs, 1regular basis to ensure sharpness of blades. The use amp for sheep, and 1.25 amps for cattle.341,376 Denicourtof plastic cones to restrain animals appears to reduce et al377 report that 110 V at 60 Hz applied for 3 secondsdistress from handling, minimizes the chance of injury was effective for pigs up to 125 kg (275 lb).to personnel, and improves positioning of the animal. In the 2-step method an electrical current is passedDecapitation of amphibians, finfish, and reptiles is ad- through the head to induce unconsciousness, then adressed elsewhere in the Guidelines. Those responsible second current is passed through either the side of thefor the use of this method must ensure that personnel body or the brisket to induce cardiac arrest.378,379 Ap-who perform decapitation have been properly trained plying the second current by an electrode placed on theto do so and are monitored for competence. side of the body behind the forelimb has been reported to be effective.49M3.8 ELECTROCUTION A common cause of failure to induce unconscious- Alternating current has been used to euthanize ness is incorrect placement of the electrodes.374 Ex-dogs, cattle, sheep, goats, swine, chickens, foxes, mink, periments with dogs revealed that electrode positionsand finfish.45,54,342,345,359–366 Fifty- or 60-cycle electrical where the brain is bypassed do not cause instantaneouscurrent is more effective than higher frequencies.367,368 unconsciousness. When electricity passes only betweenElectrocution induces death by cardiac fibrillation, the forelimbs and hind limbs or neck and feet, it causeswhich causes cerebral hypoxia.365,366,369 However, ani- the heart to fibrillate but does not induce sudden loss ofmals do not lose consciousness for 10 to 30 seconds consciousness.369 The animal will be electrocuted, butor more after onset of cardiac fibrillation. It is impera- will remain conscious until it dies from cardiac fibril-tive that animals be unconscious and insensible to pain lation.before being electrocuted. Unconsciousness can be in- Three options are available for correct electrodeduced by any method that is acceptable or acceptable placement for the head-only method, including on bothwith conditions, including passing a current through sides of the head between the eye and ear, the base ofthe brain.370 the ear on both sides of the head, and diagonally below Parameters for use of electricity to induce uncon- one ear and above the eye on the opposite side of thesciousness are readily available.342,371 When electricity head. For the 1-step (head-to-back) method, the headis used to induce unconsciousness, a current is passed electrode may be placed on the forehead or immedi-through the brain, which will induce a grand mal epi- ately behind the ear. The head electrode should neverleptic seizure.106,363,366,372 Signs of effective induction of be placed on the neck because the brain will be by-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 39
  • 40. passed.100 Diagonal movement of the electrical current M3.9 KILL TRAPSthrough the body can be accomplished by placing the Mechanical kill traps are used for the collectionhead electrode behind one ear and the body electrode and killing of small, free-ranging mammals for com-on the opposite side. When the 2-step procedure is mercial purposes (fur, skin, or meat), scientific pur-used, placement of the body electrode behind the fore- poses, to stop property damage, and to protect humanlimb is effective.49 Electrodes consisting of a metal band safety. Their use remains controversial and kill traps door chain around the nose and a band or chain around not always render a rapid or stress-free death consis-the thorax appear to be effective for pigs weighing up tent with the criteria established for euthanasia by theto 125 kg.377 POE.380 For this reason, use of live traps followed by When electrical methods of euthanasia are used, other methods of euthanasia is preferred. There are athe following signs of return to consciousness must few situations when that is not possible (eg, pest con-be absent: rhythmic breathing, righting reflex, vocal- trol) or when it may actually be more stressful for theization, eyeblink, and tracking of a moving object.49 animals or dangerous for humans to use live traps.Gasping and nystagmus may be present in animals that Although newer technologies are improving kill traphave been successfully rendered unconscious with elec- performance in achieving loss of consciousness quickly,tricity. Gasping should not be confused with rhythmic individual testing is recommended to be sure the trap isbreathing, and nystagmus (a rapid vibrating or flutter- working properly.381 If kill traps must be used, the mosting of the eye) should not be confused with eyeblink humane option available must be chosen,382–384 as evalu-(complete closure and then complete opening of the ated by use of International Organization for Standard-eye, which occurs without touching). ization testing procedures,385 or by the methods of Gil- bert,386 Proulx et al,387,388 or Hiltz and Roy.389 Advantages—(1) Electrocution is humane if the To reach the required level of efficacy, traps mayanimal is first rendered unconscious. (2) It does not need to be modified from manufacturers’ productionchemically contaminate tissues. (3) It is economical. standards. In addition, as specified in scientific stud- ies, trap placement (ground vs tree sets), bait type, set Disadvantages—(1) Electrocution may be hazard- location, selectivity apparatus, body placement modi-ous to personnel. (2) It is not useful for dangerous, in- fying devices (eg, sidewings, cones), trigger sensitivity,tractable animals that are difficult to restrain. (3) It is and trigger type, size, and conformation are essentialaesthetically objectionable because of violent extension considerations that could affect a kill trap’s ability toand stiffening of the limbs, head, and neck. (4) It may reach these standards. Several kill traps, modifications,not result in death in small animals (< 5 kg [11 lb]) and set specifics have been scientifically evaluated andbecause ventricular fibrillation and circulatory collapse found to meet standards for various species.387,388,390–403,fdo not always persist after cessation of current flow. (5)Sometimes it is not effective in dehydrated animals.371 Advantage—(1) Free-ranging small mammals may(6) Personnel must be familiar with appropriate place- be killed with minimal distress associated with han-ment of electrodes and use of equipment. (7) Purpose- dling and human contact. (2) Multiple animals may bebuilt equipment must be used. effectively killed in situations where public health, ani- mal behavior, or other constraints exist. General recommendations—Euthanasia by electro-cution is acceptable with conditions. It requires spe- Disadvantages—(1) Traps may not kill within ac-cial skills and equipment that will ensure passage of ceptable time periods. (2) Selectivity and efficiency issufficient current through the brain to induce loss of dependent on the skill and proficiency of the operator.consciousness and induce tonic and clonic epileptic (3) Nontarget species may be trapped and injured.spasms. Unconsciousness must be induced before car-diac fibrillation or simultaneously with cardiac fibrilla- General recommendations—Kill traps do not consis-tion. Cardiac fibrillation must never occur before the tently meet the POE’s criteria for euthanasia, and mayanimal is rendered unconscious. Methods that apply be best characterized as humane killing under someelectric current from head to tail, head to foot, or head circumstances. At the same time, it is recognized theyto moistened metal plates on which the animal stands can be practical and effective for scientific animal col-are unacceptable. The 2-step method should be used lection or pest control when used in a manner that en-in situations where there may be questions about suf- sures selectivity, a swift kill, and no damage to bodyficient current to induce a grand mal seizure with tonic parts needed for field research.404,405 Care must be takenand clonic spasms. This approach enables observation to avoid trapping and injuring nontarget species.of tonic and clonic spasms before a second current is ap- Traps need to be checked at least once daily. Inplied to induce cardiac arrest. Although acceptable with those instances when an animal is wounded or capturedconditions if the aforementioned requirements are met, but not dead, the animal must be killed quickly and hu-the method’s disadvantages outweigh its advantages in manely. Kill traps should be used only when other ac-most applications. Electroimmobilization that paralyz- ceptable methods are not practical or have failed. Trapses an animal without first inducing unconsciousness is for nocturnal species should not be activated during theextremely aversive and is unacceptable.370,371 For both day to avoid capture of diurnal species.404 Trap manu-humane and safety reasons, the use of household elec- facturers should strive to meet their responsibility oftrical cords is not acceptable. minimizing pain and suffering in target species. Traps that entrap a conscious animal in glue or other sticky40 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 41. substance are not acceptable for euthanasia, but may be is the most effective method to fix brain tissue in vivorequired for pest control. Glue traps are acceptable for for subsequent assay of enzymatically labile chemicals.insects or spiders. Disadvantages—(1) Instruments are expensive. (2)M3.10 MACERATION Only animals the size of mice and rats can be eutha- Maceration, via use of a specially designed me- nized with commercial instruments that are currentlychanical apparatus having rotating blades or projec- available.tions, causes immediate fragmentation and death ofpoultry up to 72 hours old and embryonated eggs. A General recommendations—Focused beam micro-review406 of the use of commercially available macera- wave irradiation is a humane method for euthanizingtors for euthanasia of chicks, poults, and pipped eggs small laboratory rodents if instruments that induce rap-indicates that death by maceration in poultry up to 72 id loss of consciousness are used. Only instruments thathours old occurs immediately with minimal pain and are designed for this use and have appropriate powerdistress. Maceration is an alternative to the use of CO2 and microwave distribution can be used. Microwavefor euthanasia of poultry up to 72 hours old. Macera- ovens designed for domestic and institutional kitchenstion is believed to be equivalent to cervical dislocation are unacceptable for euthanasia.and cranial compression as to time element, and isconsidered to be an acceptable means of euthanasia for M3.12 THORACIC (CARDIOPULMONARY,newly hatched poultry by the Federation of Animal Sci- CARDIAC) COMPRESSIONence Societies,407 Agriculture Canada,408 World Organ- Thoracic (cardiopulmonary, cardiac) compressionisation for Animal Health,342 and European Union.409 is a method that has been used by biologists to termi- nate the lives of wild small mammals and birds, mainly Advantages—(1) Death is almost instantaneous. under field conditions. Although it has been used ex-(2) The method is safe for workers. (3) Large numbers tensively in the field, data supporting this method areof animals can be killed quickly. not available, including degree of distress induced and time to unconsciousness or death. Based on current Disadvantages—(1) Special equipment is required knowledge of the physiology of both small mammalsand it must be kept in excellent working condition. (2) and birds, thoracic compression can result in substan-Personnel must be trained to ensure proper operation tial pain and distress before animals become uncon-of equipment. (3) Macerated tissues may present bios- scious, thus lacking key humane considerations thatecurity risks. can be addressed by other methods. Various veterinary and allied groups do not support thoracic compression General recommendations—Maceration requires as a method of euthanasia.413–416 Consequently, thoracicspecial equipment that must be kept in excellent work- compression is an unacceptable means of euthanizinging order. Chicks must be delivered to the macerator animals that are not deeply anesthetized or insentientin a way and at a rate that prevents a backlog of chicks due to other reasons, but is appropriate as a secondaryat the point of entry into the macerator and without method for animals that are insentient.causing injury, suffocation, or avoidable distress to the The consensus of veterinarians with field biologychicks before maceration. training and expertise is that portable equipment and alternate methods are currently available to field biolo-M3.11 FOCUSED BEAM gists for euthanasia of wildlife under field conditions,MICROWAVE IRRADIATION in accordance with current standards for good animal Heating by focused beam microwave irradiation is welfare. Anesthetics can be administered prior to ap-used primarily by neurobiologists to fix brain metabo- plication of thoracic compression. Depending on taxa,lites in vivo while maintaining the anatomic integrity of open-drop methods or injectable agents that do notthe brain.410 Microwave instruments have been specifi- require DEA registration can be used. These alternatecally designed for use in euthanasia of laboratory mice methods are generally practical to use with minimaland rats. The instruments differ in design from kitchen training and preparation as standard procedures priorunits and may vary in maximal power output from 1.3 to embarking upon fieldwork.to 10 kW. All units direct their microwave energy tothe head of the animal. The power required to rapidly M3.13 ADJUNCTIVE METHODShalt brain enzyme activity depends on the efficiency ofthe unit, the ability to tune the resonant cavity, and the M3.13.1 Exsanguinationsize of the rodent head.411 There is considerable varia- Exsanguination can be used to ensure death sub-tion among instruments in the time required for loss sequent to stunning, or in otherwise unconscious ani-of consciousness and euthanasia. A 10-kW, 2,450-MHz mals. Because anxiety is associated with extreme hy-instrument operated at a power of 9 kW will increase povolemia, exsanguination must not be used as a solethe brain temperature of 18- to 28-g mice to 79°C in means of euthanasia.417 Animals may be exsanguinated330 milliseconds, and the brain temperature of 250- to to obtain blood products, but only when they are se-420-g rats to 94°C in 800 milliseconds.412 dated, stunned, or anesthetized.418 Advantages—(1) Loss of consciousness is achieved M3.13.2 Pithingin < 100 milliseconds, and death in < 1 second. (2) This Pithing is used as an adjunctive procedure to en-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 41
  • 42. sure death in an animal that has been rendered uncon- advance of exsanguination to reduce involuntary move-scious by other means. ment in stunned animals.420 This method should not be Pithing in ruminants is performed by inserting a used in ruminants intended for food because of possiblepithing rod or tool through the entry site produced in contamination of the meat with specified risk materials.the skull by a penetrating captive bolt or free bullet.419 Disposable pithing rods are available for purchase.The operator manipulates the pithing tool to substan- The rod must be somewhat rigid, yet flexible, and oftially destroy both brainstem and spinal cord tissue. sufficient length to reach the brain and spinal columnMuscular activity during pithing can be considerable, through the access point in the skull.but is followed by quiescence that facilitates exsanguina- Pithing of frogs and other amphibians is stronglytion or other procedures. Pithing is sometimes used in discouraged, unless the patient is anesthetized first.42 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 43. Part III—Methods of Euthanasiaby Species and EnvironmentS1. COMPANION ANIMALS state (eg, animal control officers, animal care techni- Methods acceptable with conditions are equivalent cians in laboratories, certified euthanasia techniciansto acceptable methods when all criteria for application in shelters in some states), as does the amount of vet-of a method can be met. erinary supervision required. Euthanizing large num- bers of animals on a regular basis can be stressful andS1.1 GENERAL CONSIDERATIONS may result in symptoms of compassion fatigue.123 To Companion animals for which euthanasia is de- minimize the stress and demands of this duty, trainedtermined to be necessary are usually encountered in personnel must be assured that they are performing4 main environments: individually owned animals; euthanasia in the most humane manner possible. Thisbreeding animals (from dams, sires, and single litters requires an organizational commitment to provide on-to colonies of breeding animals); populations of ani- going professional training on the latest methods andmals maintained in animal control facilities, shelters materials available for euthanasia and effective man- agement of compassion fatigue for all personnel.121 Inand rescues, and pet shops; and animals maintained in addition, personnel should be familiar with methodsresearch laboratories. Examples of less common ven- of restraint and euthanasia for all species likely to beues in which companion animals might be euthanized encountered in their facility.include quarantine stations and Greyhound racetracks. Areas where euthanasia is conducted in institu-Aquatic companion animals are considered in Section tional settings should be isolated from other activities,S6, Finfish and Aquatic Invertebrates, of the Guidelines. where possible, to minimize stress on animals and toAs indicated previously in this document (see Section provide staff with a professional and dedicated workI5.5, Human Behavior), the relationships between com- area. A well-designed euthanasia space provides goodpanion animals and their owners or caretakers vary and lighting with the ability to dim or brighten as required,should be carefully considered and respected when se- ventilation, adaptable fixtures, and adequate space forlecting an approach to euthanasia for these species. at least two people to move around freely in different Euthanasia of companion animals is best conducted types of animal-handling situations.121,423 Attemptsin quiet, familiar environments when practical. The spe- should be made to minimize smells, sights, and soundscies being euthanized, the reason for euthanasia, and the that may be stressors for animals being euthanized. Ba-availability of equipment and personnel will all contrib- sic equipment for handling and restraint, a scale, clip-ute to decisions about the most appropriate location. pers, tourniquets, stethoscope, cleaning supplies, a va-The professional judgment of the veterinarian conduct- riety of needles and syringes, and body bags should being or providing oversight for euthanasia is paramount readily available to accommodate the needs of poten-in making appropriate decisions about euthanasia (eg, tially diverse animal populations. In addition, a first-aidlocation, agent, route of administration) in species kept kit should be available to address minor human inju-as companions and in the specific environments where ries, and medical attention should always be sought forthey are encountered. Personnel conducting euthanasia bite injuries and more serious human injuries.must have a complete understanding of and proficiency Euthanasia protocols for companion animals (usu-in the euthanasia method to be used. ally dogs and cats) in institutional settings (eg, shelters, For individually owned companion animals, eu- large breeding facilities, research facilities, quarantinethanasia will often be conducted in a private room in facilities, racetracks) may differ from those applied ina veterinary clinic or in the home, to minimize animal traditional companion animal clinical practices due toand owner distress.421 Factors leading to the decision to situation-specific requirements, including variable ac-euthanize should be discussed openly,109 and the ani- cess to pharmaceuticals and other equipment, diagnos-mal’s owner should be permitted to be present during tic and research needs (eg, postmortem tissue samples),euthanasia whenever feasible. Owners should be fully and the number of animals to be euthanized. For thisinformed about the process they are about to observe, reason, general recommendations about euthanasiaincluding the potential for excitation during anesthe- methods applicable to companion animals are followedsia and other possible complications.421,422 If one eu- by more specific information as to their applicability inthanasia method is proving difficult, another method frequently encountered environments. While protocolsshould be tried immediately. Euthanasia should only be may differ, the interests of the animal must be givenattempted when the necessary drugs and supplies are equal consideration whether the animal is individuallyavailable to ensure a smooth procedure and, upon veri- owned or not.fication of death, owners should be verbally notified.110 In animal control, shelter, and rescue situations; S1.2 ACCEPTABLE METHODSresearch laboratories; and other institutional settings,trained technical personnel rather than veterinarians S1.2.1 Noninhaled Agentsoften perform euthanasia. Training and monitoring of Barbiturates and barbituric acid derivatives—In-these individuals for proficiency vary by setting and travenous injection of a barbituric acid derivative (eg,AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 43
  • 44. pentobarbital, pentobarbital combination product) is and manufacturing resume in the United States forthe preferred method for euthanasia of dogs, cats, and Tributame and T-61, more attention may be focused onother small companion animals. Barbiturates adminis- the use of the latter two agents for euthanasia of dogstered IV may be given alone as the sole agent of eu- and cats.thanasia or as the second step after sedation or generalanesthesia. Refer to the product label or appropriate S1.3 ACCEPTABLE WITHspecies references424 for recommended doses. Current CONDITIONS METHODSfederal drug regulations require strict accounting forbarbiturates, and these must be used under the super- S1.3.1 Noninhaled Agentsvision of personnel registered with the US DEA. Barbiturates and barbituric acid derivatives (alter- When IV access would be distressful, dangerous, or nate routes of administration)—The IP route is not prac-impractical (eg, small patient size such as puppies, kit- tical for medium or large dogs due to the volume oftens, small dogs and cats, rodents, and some other non- agent that must be administered and a prolonged timedomestic species or behavioral considerations for some to death. A better choice for these animals when IV ac-small exotic mammals and feral domestic animals), cess is unachievable using manual restraint is generalbarbiturates and barbituric acid derivatives may be ad- anesthesia followed by intra-organ injection. In uncon-ministered IP (eg, sodium pentobarbital, secobarbital; scious or anesthetized animals, intra-organ injectionsnot pentobarbital combination products as these have (eg, intraosseous [Figure 4], intracardiac [Figure 5], in-only been approved for IV and intracardiac administra- trahepatic and intrasplenic [Figure 6], intrarenal [Fig-tion). Because of the potential for peritoneal irritationand pain (observed in rats),425 lidocaine has been usedwith some success in rats to ameliorate discomfort.426,427Lidocaine was also used in combination with sodiumpentobarbital in a laboratory comparison of IP andintrahepatic injection routes in cats from animal shel-ters.284 Additional studies are necessary to determineapplicability to and dosing for other species. Nonbarbiturate anesthetic overdose—Injectable an-esthetic overdose (eg, combination of ketamine and xy-lazine given IV, IP or IM or propofol given IV) is accept-able for euthanasia when animal size, restraint require-ments, or other circumstances indicate these drugs arethe best option for euthanasia. Assurance of death isparamount and may require a second step, such as abarbiturate, or additional doses of the anesthetic. Foradditional information see Section M2, NonInhaledAgents, and Section S2, Laboratory Animals. Figure 4—One recommended site (greater tubercle of the humer- us) for administration of an intraosseous injection in adult dogs, Tributame—While it is not currently being manu- using a bone injection gun. An alternative is to use a Jamshidi bonefactured, Tributame is an acceptable euthanasia drug for marrow needle or, in very young dogs, a hypodermic needle.dogs provided it is administered IV by an appropriatelytrained individual at recommended dosages and at prop-er injection rates. If barbiturates are not available, its ex-tralabel use in cats may be considered; however, adversereactions (eg, agonal breathing) have been reported andthe current FDA-approved Tributame label recommendsagainst its use in cats. Routes of administration otherthan IV injection are not acceptable. Aesthetically objec-tionable agonal breathing may occur in unconscious ani-mals and, consequently, the use of Tributame for owner-attended euthanasia is not recommended. While discon-certing for observers, because the animal is unconscious,agonal breathing has limited impact on its welfare. T-61—T-61 is acceptable as an agent of euthana-sia, provided it is administered appropriately by trainedindividuals. Slow IV injection is necessary to avoidmuscular paralysis prior to unconsciousness.295 Routesother than IV are unacceptable. T-61 is also not cur-rently being manufactured in the United States but is Figure 5—Site for administration of intracardiac injections in theobtainable from Canada. cat. Intracardiac injection is only appropriate in unconscious or Should sodium pentobarbital become unavailable anesthetized animals.44 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 45. section for details). Because of the potential for re- covery, care must be taken to ensure death has oc- curred prior to disposing of animal remains. Inhaled anesthetics may also be used to anesthetize small fractious animals prior to administration of an inject- able euthanasia agent. Carbon monoxide—Carbon monoxide can be used effectively for euthanasia when required conditions for administration (see detailed discussion in Inhaled Agents section of the Guidelines) can be met. These conditions can be challenging and costly to meet on a practical basis, and there is substantial risk to personnelFigure 6—Site for administration of intrahepatic and intrasplenic (hypoxia) if safety precautions are not observed. Con-injections in the dog. In this figure, the liver is being injected; the sequently, CO is acceptable with conditions for use inspleen is depicted in red caudal to the liver and stomach. Intra-hepatic and intrasplenic injections are only appropriate in uncon- institutional situations where appropriately designedscious or anesthetized animals with the exception of intrahepatic and maintained equipment and trained and monitoredinjections in cats as discussed in the text. personnel are available to administer it, but it is not recommended for routine euthanasia of cats and dogs. It may be considered in unusual or rare circumstances, such as natural disasters and large-scale disease out- breaks. Alternate methods with fewer conditions and disadvantages are recommended for companion ani- mals where feasible. Carbon dioxide—Carbon dioxide can be used effec- tively for euthanasia when required conditions for ad- ministration (see detailed discussion in Inhaled Agents section of the Guidelines) can be met. However, just as for use of CO, this can be challenging and costly to do on a practical basis. Narcosis is a human safety risk associated with the use of CO2. Carbon dioxide is ac- ceptable with conditions for use in institutional situ- ations where appropriately designed and maintained equipment and trained and monitored personnel are available to administer it, but it is not recommended for routine euthanasia of cats and dogs. It may be con-Figure 7—Site for administration of an intrarenal injection in the sidered in unusual or rare circumstances, including butdog. Intrarenal injection is only appropriate in anesthetized or un- not limited to, natural disasters and large-scale diseaseconscious animals. outbreaks. Alternate methods with fewer conditionsure 7]136,428,g) may be used as an alternative to IV or IP and disadvantages are recommended for companioninjection of barbiturates when IV access is difficult.428 animals where feasible.Intra-organ injections may speed the rate of barbiturateuptake over standard IP injections, and when an owner S1.3.3 Physical Methodsis present, this approach may be preferred over the IP Gunshot—Gunshot should only be performed byroute.429 The intrahepatic injection of a combination of highly skilled personnel trained in the use of firearmssodium pentobarbital and lidocaine in awake cats from (eg, animal control and law enforcement officers, prop-animal shelters caused rapid unconsciousness and was erly trained veterinarians) and only in jurisdictions thatmore accurately placed than IP injections.284 Therefore, allow for legal firearm use. A method acceptable withintrahepatic injection in awake cats may have limited conditions, use of gunshot may be appropriate in re-application in controlled environments when conduct- mote areas or emergency situations in which withhold-ed by trained personnel. However, positioning of awake ing death by gunshot will result in prolonged, unrelievedcats for intrahepatic injection is in an upright position pain and suffering of the animal or imminent danger towith the forequarters elevated rather than in lateral re- human life. Protocols for ensuring a humane death bycumbency. gunshot have been described344,430 and preferred anatom- ic sites for use of gunshot for dogs and cats are providedS1.3.2 Inhaled Agents in Figures 8 and 9, respectively. Pre-euthanasia sedation Inhaled anesthetics—Overdoses of inhaled an- (eg, medication added to food) is recommended, when-esthetics administered via chamber (eg, isoflurane, ever possible, for cats since they may be difficult to shootsevoflurane) are acceptable with conditions for eu- humanely.344 Gunshot is not recommended as a routinethanasia of small mammals and some other species approach to the euthanasia of dogs, cats, or other small< 7 kg because most vertebrates display aversion companion animals, and should not be used when otherbehavior to inhaled anesthetics (see Inhaled Agents methods are available and practicable.AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 45
  • 46. exposure may be necessary to ensure death. Alternate methods with fewer conditions and disadvantages are recommended whenever feasible. Electrocution—Electrocution using alternating cur- rent in dogs rendered unconscious by an acceptable means (eg, general anesthesia) may be used for eutha- nasia (see Section M3.8 of the Guidelines for details). The disadvantages of electrocution outweigh its advan- tages; therefore it is not recommended for routine use in companion animals. Alternate methods with fewer conditions and disadvantages should be used whenever feasible. S1.5 UNACCEPTABLE METHODSFigure 8—Anatomic site for gunshot in dogs is located midway With the exception of IM delivery of select inject-between the level of the eyes and base of the ears, slightly offmidline with aim directed across the dog toward the spine.344 able anesthetics, the SC, IM, intrapulmonary, and in- trathecal routes of administration are unacceptable for administration of injectable euthanasia agents because of the limited information available regarding their ef- fectiveness and high probability of pain associated with injection in awake animals. Household chemicals, disinfectants, cleaning agents, and pesticides are not acceptable for adminis- tration as euthanasia agents. Other unacceptable approaches to euthanasia in- clude hypothermia and drowning. S1.6 SPECIAL CONSIDERATIONS S1.6.1 Dangerous or Fractious AnimalsFigure 9—Anatomic site for gunshot in cats is a point slightlyventral to a line drawn between the medial bases of the ears344 or Animals that are unable to be safely and humanelythe intersection of lines drawn between lateral canthi of the eyes restrained should be sedated by means of drugs deliv-and medial bases of ears as shown. ered orally (eg, gelatin capsules for delivery of drugs in food,91 liquid formulations squirted into mouths92) Penetrating captive bolt—Use of a penetrating cap- or remotely (eg, darts, pole syringes) before adminis-tive bolt by trained personnel in a controlled laboratory tration of euthanasia agents. Doing so will assist in re-setting has been described as an effective and humane lieving anxiety and pain for the animal, in addition tomethod of euthanasia for rabbits and dogs.331 The bolt reducing safety risks for personnel. There is a varietymust be placed directly against the skull; therefore, safe of pre-euthanasia drugs that can be administered PO,and effective application of the technique may be fa- SC, or IM, alone or in combination, to render animalscilitated by pre-euthanasia sedation or anesthesia. Pen- unconscious with minimal handling in preparation foretrating captive bolt is not recommended as a routine euthanasia.431approach to the euthanasia of dogs, cats, or other smallcompanion animals, and should not be used when oth- S1.6.2 Disposal of Animal Remainser methods are available and practicable. Residues of injectable agents commonly used for euthanasia of companion animals (eg, sodium pento-S1.4 ADJUNCTIVE METHODS barbital) tend to persist in the remains and may cause Potassium chloride—Potassium chloride (1 to 2 sedation or even death of animals that consume themmol/kg, 75 to 150 mg/kg, or 1 to 2 mEq K+/kg) ad- body. For this reason safe handling and appropriate dis-ministered IV or intracardially may be used to eutha- posal of the remains are critically important. Additionalnize companion animals when they are unconscious information is available in Section I8, Disposal of Ani-(unresponsive to noxious stimuli) or under general an- mal Remains.esthesia. Use of potassium chloride in awake animals isunacceptable. S1.7 FETUSES AND NEONATES Scientific data432 indicate that mammalian embryos Nitrogen or argon—Gradual displacement methods and fetuses are in a state of unconsciousness through-using N2 or Ar, alone or with other gases, in awake dogs out pregnancy and birth. For dogs and cats, this isand cats may result in hypoxia prior to loss of conscious- in part due to moderate neurologic immaturity, withness (see Inhaled Agents section of the Guidelines for sentience being achieved several days after birth. Thedetails). Therefore, administration of N2 or Ar (< 2% precocious young of guinea pigs remain insentient andO2) should only be used as an adjunctive method for unconscious until 75% to 80% of the way through preg-unconscious or anesthetized dogs and cats; prolonged nancy and remain unconscious until after birth due to46 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 47. chemical inhibitors (eg, adenosine, allopregnanolone, agent. Use of an IV catheter prevents repeat injectionspregnanolone, prostaglandin D2, placental peptide neu- and minimizes the need for restraint while pet ownersroinhibitor) and hypoxic inhibition of cerebrocortical are present. When circulation is compromised by theactivity.432 As a consequence, embryos and fetuses can- animal’s condition and sedation or anesthesia may re-not consciously experience feelings such as breathless- duce the likelihood of successful injection, it may beness or pain. Therefore, they also “cannot suffer while necessary to proceed with IV injection in the awakedying in utero after the death of the dam, whatever the animal, or another route of administration of euthaniz-cause.”432 Information about developing nonmamma- ing agent might be considered. Alternatively, generallian eggs is available in the S5, Avians; S6, Finfish and anesthesia may be induced, followed by administrationAquatic Invertebrates; and S7, Captive and Free-Rang- of a euthanasia agent.ing Nondomestic Animals sections of the Guidelines. Euthanasia of dogs, cats, and other mammals in S1.8.2 Breeding Facilitiesmid- or late-term pregnancy should be conducted via Euthanasia protocols in large breeding facilitiesan injection of a barbiturate or barbituric acid deriva- may differ from those utilized in a clinical practice set-tive (eg, sodium pentobarbital) as previously described. ting. Indications for euthanasia in breeding facilitiesFetuses should be left undisturbed in the uterus for 15 include neonates with congenital defects, acquired ab-to 20 minutes after the bitch or queen has been con- normalities or diseases within any segment of the popu-firmed dead. This guidance is also generally applicable lation, or other conditions that render animals unsuit-to nonmammalian species, with euthanasia of eggs per able for breeding or sale. Euthanasia may be performedguidance provided in the S5, Avians; S6, Finfish and on an individual-animal basis, or in groups. EuthanasiaAquatic Invertebrates; and S7, Captive and Free-Rang- method is determined by animal species, size, age, anding Nondomestic Animals sections of the Guidelines. number of animals to be euthanized. Barbiturates areIntraperitoneal injections of pentobarbital should be commonly administred IV or IP for individual euthana-avoided whenever possible during the later stages of sia of any species, and for all ages of dogs and cats. Car-pregnancy due to the likelihood of inadvertently enter- bon dioxide euthanasia is commonly utilized for indi-ing the uterus, rendering the injection ineffective. vidual or group euthanasia of small animals, including Altricial neonatal and preweanling mammals are ferrets, rodents, and rabbits. Regardless of method andrelatively resistant to euthanasia methods that rely on number of animals being euthanized, procedures musthypoxia as their mode of action. It is also difficult, if not be performed in a professional, compassionate mannerimpossible, to gain venous access. Therefore, IP injec- by trained individuals under veterinary oversight. Ap-tion of pentobarbital is the recommended method of propriate techniques for assuring death must be appliedeuthanasia in preweanling dogs, cats, and small mam- individually, regardless of the number of animals beingmals. Intraosseous injection may also be used, if strate- euthanized.gies are used to minimize discomfort from injection byusing intraosseous catheters that may be in place (see S1.8.3 Animal Control, Sheltering,Section M2, NonInhaled Agents, of the Guidelines), or and Rescue Facilitiesif the animal is anesthetized prior to injection. The preferred method of euthanasia in these fa- During ovariohysterectomy of pregnant dogs and cilities is injection of a barbiturate or barbituric acidcats and small mammals with altricial neonates, liga- derivative with appropriate animal handling. Whention of the uterine blood vessels with retention of the euthanizing animals that are well socialized withoutfetuses inside the uterus will result in death of the fe- pre-euthanasia sedation or anesthesia, appropriate han-tuses. The resistance of altricial neonates (eg, cats, dogs, dling usually involves two trained people. One individ-mice, rats) to euthanasia methods whose mechanisms ual restrains the animal and the other administers therely on hypoxia suggests that the uterus should not be euthanasia agent.434opened for substantially longer periods than for preco- When euthanizing distressed, dangerous, or frac-cial neonates,433 perhaps 1 hour or longer. In the case tious animals, a sedative or anesthetic should be ad-of caesarian section in late-term pregnancy, IP injection ministered prior to attempting euthanasia. When theof pentobarbital is recommended for fetuses that must necessary restraint can be performed safely (appropri-be euthanized for congenital deformities or illness and ate handling techniques and equipment must be used),that have been removed from the uterus (creating the a pre-euthanasia sedative or anesthetic can be deliveredpotential that successful breathing may have occurred). IM or PO. After administration of the sedative or anes- thetic, the animal is released so that it can return to aS1.8 EUTHANASIA comfortable low-stress location (eg, dimly lighted cageIN SPECIFIC ENVIRONMENTS or area) while the drug takes effect.431 Because of the diversity of animals received by shelters, techniciansS1.8.1 Individual Animals performing euthanasia must have a good understand-in Presence of Owners ing of animal behavior and restraint, the proper use of Pre-euthanasia sedation or anesthesia should be equipment, and the variety of euthanasia drugs avail-provided whenever practicable, either before or after able and their effects.435the owner(s) has had the opportunity to spend somefinal moments with his or her pet. Once the animal is S1.8.4 Laboratory Animal Facilitiescalm, either direct venipuncture or use of an IV cath- Euthanasia for companion animals in scientific set-eter is acceptable for IV injection of the euthanizing tings must be approved by the IACUC. The IACUC hasAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 47
  • 48. mandatory veterinary input and considers animal wel- tions or pheromones that other animals in the roomfare, requirements for postmortem tissue specimens, could hear or smell may be best performed in anotherand interference of euthanasia agents or methods with location, if transportation distress can be minimized.study results. Scientific and husbandry staff form strong Similarly, wild-caught animals should be handled andemotional bonds with companion animals in scientific euthanized in the manner least stressful to the animals.settings, so sensitivity to grief and compassion fatigueis necessary. S2.2.1 Acceptable MethodsS2. LABORATORY ANIMALS S2.2.1.1 Noninhaled Agents Barbiturates and barbituric acid derivatives—Inject- Methods acceptable with conditions are equivalent able barbiturates act quickly and smoothly to renderto acceptable methods when all criteria for application rodents unconscious. If there is vascular access, IVof a method can be met. administration is preferred. The IP route is, however, most practical. Pain may be associated with injectionsS2.1 GENERAL CONSIDERATIONS given via the IP route,426,427 but the degree of pain and General comments about companion animals, the methods for controlling pain have yet to be defined.farm animals, poikilotherms, and birds are provided The euthanasia dose is typically three times the anes-elsewhere in the Guidelines, and usually apply to these thetic dose. Pentobarbital is the most commonly usedspecies in the laboratory setting. Some other commonly barbiturate for laboratory rodents because of its longused laboratory animal species are addressed later in shelf life and rapidity of action.the text. Most laboratory mammals currently used inbiomedical research are small rodents that are main- Injectable barbiturate combinations—Injectabletained in large numbers. Venous access is typically dif- barbiturates are often used in combination with localficult and injectable agents are usually delivered via the anesthetics and anticonvulsants. An adequate dose ofIP route. barbiturate is the most important component in these In addition to humane outcomes, an important combinations.consideration in the choice of method for euthanasiaof laboratory animals is the research objectives for the Dissociative agent combinations—Lethal doses ofanimals being euthanized. Euthanasia methods can dissociative agents such as ketamine are commonlylead to metabolic and histologic artifacts that may af- used in laboratory settings. In some species, ketaminefect research outcomes. For example, isoflurane may alone can result in stimulatory activity prior to seda-artificially elevate blood glucose concentrations, while tion and loss of consciousness. In conscious rodents,IP injection of barbiturates can create artifacts in intes- ketamine and similar dissociative agents should betinal tissues and/or result in alterations in reproductive used in combination with an α2-adrenergic receptorhormones.436–438 Euthanasia by inhalation of CO2 ele- agonist such as xylazine or benzodiazepines such asvates serum potassium concentrations.439 Time elapsed diazepam.452between euthanasia and tissue collection can also be acritical factor affecting choice of euthanasia method.440 S2.2.2 Acceptable With Conditions MethodsResearch needs may also require the use of an adjunc-tive method (eg, bilateral thoracotomy, exsanguination, S2.2.2.1 Inhaled Agentsperfusion with fixatives, injection of potassium chlo- Inhaled anesthetics—Halothane, isoflurane, sevo-ride). The application of such adjunctive methods is ac- flurane, or desflurane, with or without N2O, are ac-ceptable when the animal is fully anesthetized. Animals ceptable with conditions for euthanasia of laboratoryused in infectious disease studies may require special rodents. Nitrous oxide should not be used alone forhandling for animal and human health and safety. euthanasia. These agents may be useful in cases where physical restraint is difficult or impractical. When usedS2.2 SMALL LABORATORY AND WILD-CAUGHT as a sole euthanasia agent delivered via vaporizer orRODENTS (MICE, RATS, HAMSTERS, GUINEA anesthetic chamber (open-drop technique), animalsPIGS, GERBILS, DEGUS, COTTON RATS) may need to be exposed for prolonged time periods to All activities related to the euthanasia of rodents ensure death.453 All other caveats as discussed in thisdeserve consideration equivalent to the euthanasia and other sections should be followed, including rec-method itself, and may factor into the choice of meth- ommended flow rates, maintaining compatible groups,od. Laboratory rodents to be euthanized are often re- and chamber maintenance. The use of inhaled anesthet-moved from the home room and/or home cage, placed ics for preanesthesia removes the necessity for slow fill-in unfamiliar groups, and then held for a period of time ing of the chamber with CO2; however, it is importantbefore euthanasia. Activities that contribute to distress to verify that an animal is dead when inhaled agentsin rodents include transport, handling (in animals not are used for euthanasia. Death may be confirmed byaccustomed to it), disruption of compatible groups, physical examination, ensured by adjunctive physicaland elimination of established scent marks.441–451 While method, or obviated by validation of euthanasia cham-eliminating all sources of distress may not be practical bers and process.147or possible, the selected method of euthanizing rodentsshould minimize these sources of potential distress. Carbon dioxide—Carbon dioxide, with or with-Methods of euthanasia likely to elicit distress vocaliza- out premedication with inhaled anesthetics, is accept-48 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 49. able with conditions for euthanasia of small rodents. Decapitation—Decapitation is used in laboratoryCompressed CO2 gas in cylinders is the recommended settings because it yields tissues uncontaminated bysource of CO2 because gas inflow to the chamber can chemical agents. Loss of cortical function following de-be precisely regulated. An optimal flow rate for CO2 capitation is rapid and occurs within 5 to 30 secondseuthanasia systems should displace 10% to 30% of the as measured by a significant reduction in amplitudechamber or cage volume/min.152,238 Prefilled chambers recordings of visual evoked responses and EEG chang-are unacceptable. If euthanasia cannot be conducted es.51,58,59 Specialized rodent guillotines are availablein the home cage, chambers should be emptied and and must be kept clean, in good condition with sharpcleaned between uses. It is important to verify that an blades. If handled correctly, rats do not show evidenceanimal is dead after exposure to CO2.147 Death may be of hypothalamic-pituitary-adrenal axis activation fromconfirmed by physical examination, ensured by an ad- decapitation, or from being present when other rats arejunctive physical method, or obviated by calibration decapitated.455 Decapitation is acceptable with condi-and validation of the euthanasia chamber and process. tions for mice and rats. Personnel should be trained onIf an animal is not dead, CO2 narcosis must be followed anesthetized and/or dead animals to demonstrate pro-with another method of euthanasia. Addition of O2 to ficiency.CO2 will prolong the time to death and may complicatedetermination of consciousness. There appears to be Focused beam microwave irradiation—Focusedno advantage to combining O2 with CO2 for euthana- beam microwave irradiation, using a machine profes-sia.238,427 sionally designed for animal euthanasia (see Physical Methods), is acceptable with conditions for euthaniz- Carbon monoxide—Although not commonly used ing mice and rats. It is the preferred method when im-in a laboratory animal setting, CO administration is ac- mediate fixation of brain metabolites is required for re-ceptable with conditions as a method of rodent eutha- search purposes.nasia when the conditions for effective and safe use canbe met (see Inhaled Agents). S2.2.3 Unacceptable MethodsS2.2.2.2 Noninhaled Agents S2.2.3.1 Inhaled Agents Tribromoethanol—Although unavailable as a com- Nitrogen and argon—Administration of N2 or Ar ismercial or pharmaceutical-grade (United States Phar- only acceptable in anesthetized mammals, as a coexist-macopeia/National Formulary/British Pharmacopeia) ing O2 concentration of < 2% is necessary to achieveproduct, tribromoethanol is a commonly used rodent unconsciousness and death. Achieving that conditionanesthetic. Its use is controversial due to its reported is difficult. In addition, Ar has been shown to be highlyadverse effects (peritonitis and death).324 However, aversive to rats.195 With heavy sedation or anesthesia,many biomedical IACUC have approved its use in ro- it should be recognized that death may be delayed. Al-dents. Tribromoethanol is acceptable with conditions though N2 and Ar are effective, other methods of eutha-as a method for euthanasia when prepared, stored, and nasia are preferable.administered at the appropriate dosage. S2.2.3.2 Noninhaled Agents Ethanol—It has been suggested that IP injections of Potassium chloride—Intravenous or intracardiac70% ethanol might be an appropriate method of eutha- administration of potassium chloride is not acceptablenasia for mice when physical methods are not desired as a sole approach to euthanasia.or other euthanasia agents are unavailable.454 Mice in-jected with 0.5 mL of 70% ethanol demonstrated grad- Neuromuscular blocking agents—Paralytic agentsual loss of muscle control, coma, and death in 2 to 4 are unacceptable for use as sole euthanasia agents.minutes.307 While ethanol is acceptable with conditionsfor certain applications (antibody production in mice), Injectable barbiturates and neuromuscular blockingother methods discussed as being acceptable and ac- agents—Combining injectable barbiturates and neuro-ceptable with conditions in the laboratory setting are muscular blocking agents in the same syringe for ad-much preferred. Its use in larger species is unaccept- ministration is unacceptable because the neuromuscu-able. lar blocking agents may take effect before the animal is anesthetized.S2.2.2.3 Physical Methods Cervical dislocation—Cervical dislocation is used Opioids—Opioids are unacceptable for euthanasiain laboratory settings. Cervical dislocation requires of laboratory animals as they are not rapidly acting, re-neither special equipment nor transport of the animal quire high doses, and are not true anesthetic agents.and yields tissues uncontaminated by chemical agents.Loss of cortical function following cervical dislocation Urethane—Urethane is a human carcinogen andis rapid and occurs within 5 to 10 seconds as measured has a slow onset of action. It is unacceptable as a soleby a significant reduction in amplitude recordings of euthanasia agent.visual evoked responses and EEG.51,58 Cervical dislo-cation is acceptable with conditions for mice and rats α Chloralose—α Chloralose is unacceptable as a< 200 g. Personnel should be trained on anesthetized sole agent of euthanasia.and/or dead animals to demonstrate proficiency.AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 49
  • 50. S2.2.4 Fetuses and Neonates S2.3 LABORATORY FARM ANIMALS, DOGS, Rodents with altricial young, such as mice and CATS, FERRETS, AND NONHUMAN PRIMATESrats, must be differentiated from rodents with precocialyoung, such as guinea pigs. Precocial young should be S2.3.1 General Considerationstreated as adults. The research goals will often influence the choice of method of euthanasia for farm animals, dogs, cats,S2.2.4.1 Acceptable Methods and ferrets. Generally, sedation (as needed) followed by Euthanasia of the dam and fetuses—Rodent fetuses IV injectable barbiturates will be the preferred method.along with other mammals are unconscious in utero Tributame administered IV by trained personnel may beand hypoxia does not evoke a response.456 Therefore, an appropriate replacement for dogs if injectable barbi-it is unnecessary to remove fetuses for euthanasia after turates are not available. For more information on otherthe dam is euthanized. methods of euthanasia of farm and companion species, consult the appropriate sections of the guidelines.S2. Noninhaled Agents For nonhuman primates and other wild-caught or Injectable barbiturates alone and in combination with nondomesticated animals used in the laboratory, somelocal anesthetics and anticonvulsants; dissociative agents general principles apply. Again, the research being con-combined with α2-adrenergic receptor agonist or benzodi- ducted may influence the choice of euthanasia method,azepines—These agents are acceptable for use in fetuses and if the institutional animal care and use program staffor neonates. See discussion on the use of these agents is unfamiliar with a species, researchers working within adult rodents. the species may provide valuable guidance. Appropriate restraint for the species must always be applied. Stress inS2.2.4.2 Acceptable With Conditions Methods animals unfamiliar with handling should be minimized. Venous access should be established or IM agents may beS2. Inhaled agents used (delivered via remote injection equipment if neces- Inhaled anesthetics—Nonflammable volatile anes- sary) for sedation. These animals are preferentially eu-thetic agents are effective for both in utero fetuses and thanized with an injectable barbiturate.neonatal rodents. Neonatal mice may take up to 50minutes to die from CO2 exposure.273 Adequate expo- S2.3.2 Special Casessure time should be provided, or an adjunctive method When animals to be euthanized are fully anesthe-(eg, cervical dislocation, or decapitation) should be tized, adjunctive methods such as bilateral thoracoto-performed after a neonate is nonresponsive to painful my, exsanguination, perfusion, and IV or intracardiacstimuli. injection of potassium chloride are acceptable.S2. Physical Methods S2.4 LABORATORY RABBITS Hypothermia—The gradual cooling of fetuses andaltricial neonates is acceptable with conditions. As cold S2.4.1 General Considerationssurfaces can cause tissue damage and presumably pain, Rabbits will struggle and breath-hold when con-the animals should not come in direct contact with ice fronted with any unpleasant or unfamiliar odors. Thisor precooled surfaces. Hypothermia for anesthesia is makes most inhaled methods difficult to use in rabbitsnot recommended after approximately 7 days of age.457 without premedication. Wild-caught animals should beTherefore, it is also an unacceptable euthanasia meth- handled and euthanized in the manner least stressful tood in animals older than this age.458 Fetuses that are the animals.believed to be unconscious and altricial neonates < 5days of age that do not have sufficient nervous system S2.4.2 Acceptable Methodsdevelopment to perceive pain may be quickly killed byrapidly freezing in liquid N2.432,459 S2.4.2.1 Noninhaled Agents Barbiturates and barbituric acid derivatives—If rab- Decapitation—Decapitation using scissors or sharp bits are used to handling, venous access may be obtainedblades is acceptable with conditions for altricial neo- via the ear. In the case of fractious rabbits, sedation maynates (< 7 days of age). Some rodent neonates, whether be necessary to gain venous access for administration ofatricial or precocial, may have a tissue mass that is too an injectable barbiturate or injectable barbiturate com-large for some scissors. Consideration should be given bination. Barbiturates may also be administered IP. Asto the potential of pain from tissue crushing as well as indicated previously, pain may be associated with injec-to personnel safety. When appropriate, another method tions given via the IP route426,427; however, the degree ofshould be selected or an adult decapitator used. pain and methods to control it have yet to be defined. These approaches are acceptable for companion rabbits Cervical dislocation—Cervical dislocation by as well.pinching and disrupting the spinal cord in the high cer- S2.4.3 Acceptable With Conditions Methodsvical region is acceptable with conditions for fetal andneonatal mice and rats. S2.4.3.1 Inhaled Agents Inhaled anesthetics—Although rabbits breath-hold when confronted with unpleasant odors,156,298,460 ani-50 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 51. mals already under anesthesia may be euthanized by an include the African clawed frog (X laevis) and leopardoverdose of anesthetic. and bull (Rana spp) frogs. These species are best eutha- nized via a physical method while fully anesthetized. Carbon dioxide—While CO2 is an effective methodof euthanasia, its use as the sole agent in rabbits results S3. ANIMALS FARMEDin apparent distress to the rabbit. Premedication with FOR FOOD AND FIBERsedative agents will allow for the administration of CO2 Methods acceptable with conditions are equivalentfor euthanasia. to acceptable methods when all criteria for application of a method are met.S2.4.3.2 Physical Methods Cervical dislocation—Cervical dislocation is ac- 3.1 GENERAL CONSIDERATIONSceptable with conditions for rabbits when performed by While some methods of slaughter and depopula-individuals with a demonstrated high degree of tech- tion might meet the criteria for euthanasia identified bynical proficiency. The need for technical competency the POE, others will not and comments in this documentis great in heavy or mature rabbits in which the large are limited to methods used for euthanasia. The followingmuscle mass in the cervical region makes manual cervi- section relates to species of animals domesticated for agri-cal dislocation more difficult. Commercial devices de- cultural purposes, specifically cattle, sheep, goats, swine,signed to aid in rabbit cervical dislocation are available and poultry, regardless of the context in which that animaland should be evaluated for their effectiveness. is being kept or the basis for the decision to euthanize it. Handling of animals prior to euthanasia should be Penetrating captive bolt—The use of rabbit-sized as stress free as possible. This is facilitated by ensuringpenetrating captive bolts to euthanize rabbits in labo- that facilities are well designed, appropriate equipmentratory or production facilities is acceptable with con- is available, and animal handlers are properly trainedditions. The captive bolt must be maintained in clean and their performance monitored.101,105–108working order, positioned correctly, and operated safely Regardless of the method of euthanasia used, deathby trained personnel. must be confirmed before disposal of the animal’s re- mains. The most important indicator of death is lackS2.4.4 Special Cases of a heartbeat. However, because this may be difficult When rabbits to be euthanized are in a surgical to evaluate or confirm in some situations, animals canplane of anesthesia, adjunctive methods such as deliv- be observed for secondary indicators of death, whichery of potassium chloride, exsanguination, or bilateral might include lack of movement over a period of timethoracotomy are acceptable. (30 minutes beyond detection of a heart beat) or the presence of rigor mortis.S2.5 LABORATORY FINFISH, AQUATICINVERTEBRATES, AMPHIBIANS, AND REPTILES S3.2 BOVIDS AND SMALL RUMINANTS Recommending euthanasia methods for finfish,aquatic invertebrates, amphibians, and reptiles used S3.2.1 Cattlein biomedical research is challenging due to the enor-mous number of species and variations in biological S3.2.1.1 Acceptable Methodsand physiologic characteristics. Methods for euthaniz-ing species commonly used in research are discussed S3. Noninhaled Agentsin detail in the relevant sections of the Guidelines. See Barbiturates and barbituric acid derivatives—Bar-these sections for additional information. biturates act rapidly and normally induce a smooth As described in the aquatics section it is acceptable transition from consciousness to unconsciousness andfor zebrafish (Danio rerio) to be euthanized by rapid death—a desirable outcome for the operator and ob-chilling (2° to 4°C) until loss of orientation and oper- servers. Although cost may be a deterrent to the useculum movements and subsequent holding times in of barbiturates for euthanasia of large and large num-ice-chilled water, specific to finfish size and age.316,461,462 bers of animals, these agents tend to be less expensiveAdult zebrafish should be exposed for a minimum of than other injectable pharmaceuticals. Drawbacks to10 minutes and fry 4 to 7 days after fertilization (dpf) the use of barbiturates are that their administration re-for at least 20 minutes following loss of operculum quires adequate restraint of the animal, personnel whomovement. Rapid chilling (as well as MS 222) has are registered with the US DEA (and other appropriatebeen shown to be an unreliable euthanasia method for state authority where required), use by under the su-embryos < 3 dpf. To ensure embryonic lethality these pervision of a veterinarian (because their use in food ismethods should be followed with another agent such extralabel), strict control over the drug with accountingas diluted sodium or calcium hypochlorite solution.462 of the amount used,463 and fewer options for disposal ofIf necessary to ensure death of other life stages, rapid animal remains because of potential residues.chilling may be followed by either an approved adjunc-tive euthanasia method or a humane killing method. S3.2.1.2 Acceptable With Conditions MethodsUntil further research is conducted, rapid chilling is ac-ceptable with conditions for other small-bodied tropi- S3. Physical Methodscal and subtropical stenothermic species. Gunshot—Gunshot is the most common method Amphibian species commonly used in research used for on-farm euthanasia of cattle.464 Death is causedAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 51
  • 52. by destruction of brain tissue and the degree of brain be fired within close range of the skull (within 1 to 3damage inflicted by the bullet is dependent on the fire- feet), and (4) the bullet must be directed so that properarm, type of bullet (or shotshell for shotguns), and ac- anatomic placement on the skull is assured.347curacy of aim. Shotguns—Shotguns loaded with birdshot (lead or Handguns—Handguns or pistols are short-barreled steel BBs) or slugs (solid lead projectiles specifically de-firearms that may be fired with one hand. For euthana- signed for shotguns) are appropriate from a distance of 1sia, use of handguns is limited to close-range shooting to 2 yards (1 to 2 m). Although all shotguns are lethal at(within 1 to 2 feet or 30 to 60 cm) of the intended tar- close range, the preferred gauges for euthanasia of cattleget. Calibers ranging from .32 to .45 are recommended are 20, 16, or 12. Number 6 or larger birdshot or shot-for euthanasia of cattle.351 Solid-point lead bullets are gun slugs are the best choices for euthanasia of cattle.351preferable to hollow-point bullets because they are Birdshot begins to disperse as it leaves the end of the gunmore likely to traverse the skull. Hollow-point bullets barrel; however, if the operator stays within short rangeare designed to expand and fragment on impact with of the intended anatomic site, the birdshot will strike thetheir targets, which reduces the depth of penetration. skull as a compact bolus or mass of BBs with ballisticUnder ideal conditions and good penetration of the characteristics on entry that are similar to a solid leadskull, hollow-point bullets are able to cause extensive bullet. At close range, penetration of the skull is assureddamage to neural tissues; however, because penetration with massive destruction of brain tissue from the disper-of the skull is the first criterion in euthanasia, a solid sion of birdshot into the brain that results in immediatelead bullet is preferred. The .22 caliber handgun is gen- loss of consciousness and rapid death.erally not recommended for routine euthanasia of adult The Canadian study350 cited previously evaluatedcattle regardless of bullet used, because of the inability several firearms, including the .410 and 12-gauge shot-to consistently achieve desirable muzzle energies with guns. The .410 loaded with either number 4 or numberstandard commercial loads.351 6 birdshot fired from a distance of 1 m was very effec- tive and had the advantage of less recoil compared with Rifles—A rifle is a long-barreled firearm that is other firearms used. The 12-gauge shotgun loaded withusually fired from the shoulder. Unlike the barrel of a number 7 1/2 birdshot fired from a distance of 2 m fromshotgun, which has a smooth bore for shot shells, the its target was effective but considered to be more pow-bore of a rifle barrel contains a series of helical grooves erful than necessary. Results of a 1-oz rifled slug fired(called rifling) that cause the bullet to spin as it travels from a 12-gauge shotgun at a distance of 25 m failed tothrough the barrel. Rifling imparts stability to the bul- penetrate the brain not because it lacked power, ratherlet and improves accuracy. For this reason, rifles are the because of faulty shot placement. Researchers conclud-preferred firearm for euthanasia when it is necessary to ed that the rail sighting system on the shotgun was notshoot from a distance. sufficient for accurate shot placement if it was neces- Rifles are capable of delivering bullets at much sary to shoot from a distance. They also believed thathigher muzzle velocities and energies and thus are not recoil from this firearm would likely make it unpleasantthe ideal choice for euthanasia of animals in indoor or to use if it were necessary to euthanize a large numbershort-range conditions. General recommendations on of animals.350rifle selection for use in euthanasia of cattle include One advantage of euthanasia using a shotgun is.22, .223, .243, .270, .308, and others.130,350,351 Results that when properly directed the birdshot will have suf-of at least one study350 suggest that the .22 LR may ficient energy to penetrate the skull but is unlikely tonot be the best selection of a firearm for euthanasia exit the skull. In the case of a free bullet or shotgun slugof adult cattle because of poor penetration, deflection, there is always the possibility of the bullet or slug exit-and fragmentation of the bullet. Standard- and high- ing the skull, creating an injury risk for operators andvelocity bullets fired from a .22 caliber rifle at a range observers. For operator and bystander safety, the muz-of 25 m failed to penetrate skulls of steers and heif- zle of a shotgun (or any other firearm) should never beers studied. On the other hand, the .223 and .30-06 held directly against the animal’s head. Discharge of theperformed satisfactorily (eg, traversed the skull and firearm results in development of enormous pressurecaused sufficient brain damage to cause death) when within the barrel that can result in explosion of the bar-fired from a distance of 25 m.350 This is in agreement rel if the muzzle end is obstructed or blocked.with similar information indicating that .22 Magnumor larger-caliber firearms provide higher muzzle ener- Penetrating captive bolt—Penetrating captive boltsgies and more consistent results when delivered to the are used for euthanasia of mature cattle in field situa-proper anatomic site.130 tions. Styles include in-line (cylindrical) and pistol grip When the most appropriate firearm is being chosen (resembling a handgun) versions. Pneumatic captivefor the purpose of euthanasia, there are several factors bolt guns (air powered) are limited to use in slaughterto be considered, including caliber of the firearm, type plant environments. Models using gunpowder chargesof bullet or shotshell, distance from the target, age of are more often used in farm environments. They consistthe animal (aged animals have harder skulls), sex of the of a steel bolt and piston at one end, housed within aanimal (bull or cow), and accuracy of aim. Based upon barrel. Upon firing, the rapid expansion of gas withinavailable information, if a .22 LR is to be used the fol- the breech and barrel propels the piston forward driv-lowing conditions apply: (1) the firearm of choice is a ing the bolt through the muzzle. A series of cushionsrifle, (2) a solid-point bullet should be used, (3) it must are strategically located within the barrel to dissipate52 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 53. excess energy of the bolt. Depending upon model, the Visual indicators that an animal has been renderedbolt may automatically retract or require manual place- unconscious from captive bolt or gunshot include thement back into the barrel through the muzzle. Accu- following: immediate collapse; brief tetanic spasms fol-rate placement over the ideal anatomic site, energy (ie, lowed by uncoordinated hind limb movements; imme-bolt velocity), and depth of penetration of the bolt de- diate and sustained cessation of rhythmic breathing;termine effectiveness of the device to cause a loss of lack of coordinated attempts to rise; absence of vocal-consciousness and death. Bolt velocity is dependent on ization; glazed or glassy appearance to the eyes; andmaintenance of the captive bolt gun (cleaning and re- absence of eye reflexes.101 Nervous system control ofplacement of worn parts), as well as proper storage of the blink or corneal reflex is located in the brainstem;the cartridge charges. Bolt velocities of 55 to 58 m/s therefore, the presence of a corneal reflex is highly sug-are desirable for effective captive bolt use in slaughter gestive that an animal is still conscious.plants.332,333,465,466 Recommended minimum bolt veloci-ties proposed for shooting bulls are as high as 70 m/s. Anatomic landmarks for use of the penetrating cap-In slaughter plants where bolt velocity is of particular tive bolt and gunshot—In cattle, the point of entry of theconcern, bolt velocity is routinely monitored to assure projectile should be at the intersection of two imagi-proper function of these devices.467 nary lines, each drawn from the outside corner of the In general, captive bolt guns, whether penetrating eye to the center of the base of the opposite horn, oror nonpenetrating, induce immediate loss of conscious- an equivalent position in polled animals (Figure 10).342ness, but death is not always assured with the use ofthis device alone. In a study of 1,826 fed steers and heif-ers only 3 (0.16%) had signs of a return to sensibility orconsciousness.336 Results were similar in observationsof 692 bulls and cows where 8 (1.2%) animals had signsconsistent with a return to consciousness.336 Failure toachieve a 100% loss of consciousness with no returnto a conscious mental state was attributed to storage ofthe captive bolt charges in a damp location, poor main-tenance of firing pins, inexperienced personnel oper-ating the captive bolt (use of the incorrect anatomicsite), misfires associated with a dirty trigger on the cap-tive bolt, and use of the device on cows and bulls withthick, heavy skulls.336 At the present time, an adjunctive method such asexsanguination, pithing, or the IV injection of a saturat-ed solution of potassium chloride is recommended toensure death when penetrating captive bolt is used.347 Anewer version of penetrating captive bolt has emergedin recent years.130 This device is equipped with an ex-tended bolt with sufficient length and cartridge powerto increase damage to the brain, including the brain-stem. This device is being studied at the present timeand may offer a euthanasia option with the penetratingcaptive bolt that does not require the need for an ad-junctive method. Captive bolt guns are attractive options for eutha-nasia because they offer a greater degree of safety tothe operator and bystanders; but they should only beused by trained people. The muzzle should always bepointed toward the ground and away from the body orbystanders in case of accidental discharge. Protectivegear for both ears and eyes is strongly recommended. Unlike techniques described for gunshot, the ani-mal must be restrained for accurate placement of thecaptive bolt. And, unlike use of a firearm, proper use ofthe captive bolt requires that the muzzle of the device beheld firmly against the animal’s head. Once the animalis restrained, discharge of the captive bolt should occur Figure 10—Anatomic site for gunshot or placement of a captivewith little or no delay so that animal distress is mini- bolt and desired path of the projectile in cattle. The point of entry of the projectile should be at the intersection of two imaginarymized. Adjunctive methods should be implemented as lines, each drawn from the outside corner of the eye to the cen-soon as the animal is rendered unconscious to avoid a ter of the base of the opposite horn, or an equivalent positionpossible return to sensibility. Thus, when conducting in polled animals. (Adapted with permission from Shearer JK, Nicoletti P Anatomical landmarks. Available at: www.vetmed.ia- .euthanasia by captive bolt, preplanning and prepara- state.edu/vdpam/extension/dairy/programs/humane-euthanasia/tion improves the likelihood of a successful outcome. anatomical-landmarks. Accessed Jun 24, 2011.)AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 53
  • 54. Firearms should be positioned so that the muzzle is Magnesium sulfate may be administered similarlyperpendicular to the skull to avoid ricochet. Proper po- to potassium chloride. Death may not occur as rapidly,sitioning of the firearm or penetrating captive bolt is but similar to administration of potassium chloride,necessary to achieve the desired results. residue risks for predators and scavengers are low (see Use of the poll (bony protuberance on the top of Noninhaled Agents).the skull) for application of the penetrating captivebolt in slaughter plants is not allowed by regulations S3. Physical Methodsin the European Union because the depth of concus- Second shot—Although one well-placed bullet orsion in this region is less than that observed in frontal shot from a penetrating captive bolt usually results insites.468 Conversely, for large bulls and water buffalo use immediate loss of consciousness with little likelihood ofof the frontal site for administration of a captive bolt return to consciousness, one should always be preparedis not always effective because of the thickness of the to deliver a second or even a third shot if necessary. Thehide and skull in this region. Use of the poll position additional injury to brain tissue along with increasedcan be effective if the appropriate captive bolt gun is hemorrhage and edema creates substantial intracranialused and when the muzzle is directed so that the dis- pressure. Compression resulting from this increase incharged bolt will enter the brain;469 however, in most pressure interrupts centers in the brain that control re-cases the poll position is not preferred. Research has spiratory and cardiac functions and leads to death.demonstrated that use of the penetrating captive boltat the poll is prone to operator error and misdirection Exsanguination—Exsanguination may be per-of the bolt into the spinal cord instead of the brain.469 formed as an adjunctive measure to ensure death whenMore animals were not properly rendered unconscious necessary in an unconscious animal. Exsanguination(ie, depth of concussion was shallow) using the poll is usually accomplished via an incision of the ventralposition as compared with frontal sites. aspect of the throat or neck transecting skin, muscle, Placement of the captive bolt is critical to ensure trachea, esophagus, carotid arteries, jugular veins, andthat the bolt enters the brain and not the spinal cord. a multitude of sensory and motor nerves and otherShots from the poll should be directed toward the base vessels. This procedure is not recommended as a soleof the tongue unless brainstem tissues are needed for method of euthanasia; rather it is reserved for use as andiagnostic reasons. Whether poll shooting is conducted adjunctive method to ensure death since informationby penetrating captive bolt or gunshot, there is sub- in the literature is inconsistent as to the length of timestantial potential for misdirection of the bullet or bolt between the neck cut and loss of consciousness. Someand damage to the brain to achieve unconsciousness or studies418,470 demonstrate a rapid loss of brain activitydeath is not assured. This will result in delays in loss of (measured by EEG) with little variation between indi-consciousness and a greater likelihood of variable peri- vidual animals. In contrast, direct observation of timeods of extreme distress. to collapse and EEG data indicate that the time from ventral-neck incision to unconsciousness is variableS3.2.1.3 Adjunctive Methods and may be quite prolonged in animals killed by exsan- guination.417,471–474S3. Noninhaled Agents Uncertainty in the time from the neck incision to Potassium chloride and magnesium sulfate—While loss of consciousness raises obvious questions: Doesnot acceptable as a sole method of euthanasia, rapid IV the animal feel pain during the neck cut? Does the dropinjection of potassium chloride may assist in ensuring in blood pressure cause discomfort or distress? Opin-death after cattle have been rendered unconscious by ions on these questions remain divided. Some hold thepenetrating captive bolt, gunshot, or administration of view that when the knife (sakin in Hebrew) is of ap-general anesthetics (α-2-adrenergic agents such as xy- propriate size, exceptionally sharp, completely free oflazine alone are insufficient; see comments under Un- blemishes or imperfections, and used in such manneracceptable methods). Normally, injection of 120 to 250 as to create a rapid clean incision (such as performedmL of a saturated solution of potassium chloride is suf- by a shochet), exsanguination is relatively painless.475ficient to cause death; however, the potassium chloride Others contend that tissues of the neck are well inner-solution should be administered until death is assured. vated with nocioceptive nerve fibers such that transec-When conducting euthanasia of cattle that may require tion leads to significant pain and distress sufficient tosubsequent administration of potassium chloride, the cause shock at the time of incision.476–478operator should prepare at least 3 to four 60-mL syring- In recognition that this issue remains controversiales of solution (equipped with 14- or 16-gauge needles) and that people conducting these procedures for thein advance. This will facilitate rapid administration and purposes of euthanasia are not likely to have a sakinensure the animal does not regain consciousness. Any or the skills of a shochet, the recommendation is thatavailable vein may be used; however, it is important to exsanguination only be used in unconscious animalsposition oneself out of the reach of limbs and hooves as an adjunctive method to assure death. It should bethat may cause injury during periods of involuntary performed with a pointed, very sharp knife with a rigidmovement. In most cases, it is safest to kneel down near blade at least 6 inches long and conducted as soon asthe animal’s back and close to the animal’s head where the loss of consciousness is confirmed.one can reach over the neck to administer the injection Exsanguination can be disturbing to observe due tointo the jugular vein. Once the needle is in the vein, the the large volume of blood loss; this also raises biosecu-injection should be delivered rapidly. rity concerns. When only the carotid arteries and jugular54 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 55. veins are cut, bleeding may persist at variable rates for the gun never be held flush with the skull. Instead, theseveral minutes. Severing these vessels closer to the tho- muzzle of the gun should be aimed in the desired direc-racic inlet where the vessels are larger will increase blood tion and held no closer than 6 to 12 inches from theflow rate. Some evidence suggests that restricted blood target.flow may be caused by the formation of false aneurysmsin the severed ends of arteries in cattle.474 Penetrating and nonpenetrating captive bolts—The principal anatomic sites for application of captive bolts Pithing—Pithing is a technique designed to cause in small ruminants are the frontal and poll positionsdeath by increasing destruction of brain and spinal (Figure 11). In sheep with horns, the poll position iscord tissue. It is performed by inserting a pithing rodthrough the entry site produced in the skull by a bulletor penetrating captive bolt. The operator manipulatesthe pithing tool to destroy brainstem and spinal cordtissue to ensure death (see Physical Methods). Mus-cular activity during the pithing process is often quiteviolent, but is followed by quiescence that facilitatesexsanguination or other procedures.420S3.2.2 Sheep and Goats Euthanasia of small ruminants may be necessaryfor reasons ranging from traumatic injury to incurabledisease. Methods include barbiturate overdose, gun-shot, or captive bolt followed by an adjunctive methodsuch as exsanguination, IV administration of potassiumchloride or magnesium sulfate, or pithing. Electrocu-tion is another option, but this method requires spe-cialized equipment to restrain the animal for properplacement of the electrodes. Because electricity and thenecessary equipment are unlikely to be available foreuthanasia under field conditions, electrocution is notconsidered to be practical for routine use.S3.2.2.1 Acceptable MethodsS3. Noninhaled Agents Barbiturates and barbituric acid derivatives—Barbi-turates act by depression of the CNS, which progressesfrom a state of consciousness to unconsciousness, deepanesthesia, and eventually death. Although use of theseagents requires restraint and involves mild discomfort(ie needle placement) for administration, observersgenerally find this a more acceptable method of eu-thanasia because death comes about more peacefully.In the companion animal setting, these attributes arehighly desirable. In production settings, concerns forcost and disposal of animal remains make this methoda less attractive euthanasia option.S3.2.2.2 Acceptable With Conditions MethodsS3. Physical Methods Figure 11—Anatomic sites for gunshot or placement of captive Gunshot—Firearms recommended for euthanasia bolts and desired path of the projectile in sheep and goats. For polled sheep (top), the proper site is at or slightly behind the pollof adult small ruminants include the .22 LR rifle; .38 aiming toward the angle of the jaw (ie, base of tongue). For heav-Special, .357 Magnum, and 9 mm or equivalent hand- ily horned rams or ewes (bottom), the proper site is high on theguns; and shotguns. Some prefer hollow-point bullets forehead aiming toward the foramen magnum (or spinal canal) or, alternatively, at or slightly behind the poll (i.e., behind the bonyto increase brain destruction and reduce the chance of ridge between the horns) aiming toward the angle of the jaw orricochet. However, operators are reminded that bullet base of the tongue. The brain of a mature goat lies in a more cau-fragmentation may substantially reduce the potential dal position in the skull than one would expect. The proper site for use of the penetrating captive bolt or free bullet is from behindfor brain destruction because of reduced penetration, the poll aiming toward the muzzle and lower part of the chin. Inparticularly when used in large-horned adult rams. mature horned sheep and goats the hardness of the skull mayShotguns or higher-caliber firearms loaded with solid- deflect some projectiles. (Adapted with permission from Shearer JK, Nicoletti P Anatomical landmarks. Available at: www.vetmed. .point bullets are preferred in these conditions. When iastate.edu/vdpam/extension/dairy/programs/humane-euthana-firearms are used for euthanasia it is important that sia/anatomical-landmarks. Accessed Jun 24, 2011.)AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 55
  • 56. often preferred. Use of a captive bolt in the poll position S3. Physical Methodswas evaluated, using 8 anesthetized sheep.468 Projection Second shot—Although one well-placed bullet orof the shot was on a line running between the bases of shot from a penetrating captive bolt usually results inthe ears and aiming toward the throat. Cortical visual immediate loss of consciousness with little likelihoodevoked responses (ie, measures of light flash–evoked of return to consciousness, one should always be pre-responses in the electrocorticogram) were evaluated to pared to deliver a second or even a third shot if neces-determine effectiveness. Visual evoked responses were sary. The additional injury to brain tissue along withabolished in all animals immediately following shoot- increased hemorrhage and edema creates sufficienting with the captive bolt. However, in 5 of the 8 sheep, intracranial pressure to cause death in most cases, butvisual evoked responses were recovered after approxi- damage to the brainstem should always be the objectivemately 50 seconds. These results indicate that using the in euthanasia.poll position for application of captive bolts to sheepmay be associated with rapid recovery of brain func- Exsanguination—Exsanguination may be per-tion. Therefore, adjunctive methods to ensure death formed as an adjunctive step to ensure death when nec-should be applied immediately following loss of con- essary in small ruminants. It may be accomplished viasciousness in small ruminants. an incision of the ventral aspect of the throat or neck Effective application of the captive bolt in sheep transecting skin, muscle, trachea, esophagus, carotidand goats is indicated by immediate loss of conscious- arteries, and jugular veins. Exsanguination should beness lasting until death by exsanguination or another performed with a pointed, very sharp knife with a rigidadjunctive method. While it is presumed that penetra- blade at least 6 inches long.tion of the bolt causes insensibility, research into the Exsanguination can be disturbing for bystandersdeterminants of effective captive bolt use indicates that because of the large volume of blood loss, which alsothe impact of the bolt on the cranium is a principal raises biosecurity concerns. When only the carotid ar-contributor to the loss of consciousness.333 The use of teries and jugular veins are cut, bleeding may persist atconcussive methods (nonpenetrating captive bolt) has variable rates for several minutes. Severing these ves-been determined to be an effective means of inducing sels closer to the thoracic inlet where the vessels areinsensibility that will persist until death caused by ex- larger will increase blood flow rate.sanguination.465 Pithing—Pithing is a technique designed to cause Anatomic landmarks for captive bolts and gunshot— death by increasing destruction of brain and spinalThe location for placement of a captive bolt or entry cord tissue. It is performed by inserting a pithing rodof a free bullet for euthanasia is similar for both sheep through the entry site produced in the skull by a bulletand goats. The optimal position for hornless sheep and or penetrating captive bolt. The operator manipulatesgoats is the top of the head on the midline.342 An al- the pithing tool to destroy brainstem and spinal cordternate site is the frontal region.342 For heavily horned tissue to ensure death (see Physical Methods). Mus-sheep and goats, the optimal site is behind the poll aim- cular activity during the pithing process is often quiteing toward the angle of the jaw.342 violent, but is followed by quiescence that facilitates exsanguination or other procedures.420S3.2.2.3 Adjunctive Methods S3.2.2.4 Unacceptable MethodsS3. Noninhaled Agents The following methods are unacceptable for eutha- Potassium chloride and magnesium sulfate—Al- nasia of cattle and small ruminants: manually appliedthough not acceptable as a sole method of euthanasia, blunt trauma to the head; injection of chemical agentsthe rapid IV injection of potassium chloride is an ef- into conscious animals (eg, disinfectants, electrolytesfective method to ensure death in sheep and goats pre- such as potassium chloride and magnesium sulfate,viously rendered unconscious by penetrating or non- nonanesthetic pharmaceutical agents); administrationpenetrating captive bolt, gunshot, or administration of xylazine or any other α2 adrenergic receptor ago-of anesthetics. When conducting euthanasia of sheep nist followed by IV potassium chloride or magnesiumand goats that may require subsequent administration sulfate (although large doses of α2 adrenergic receptorof potassium chloride, the operator should prepare at agonists can produce a state resembling general anes-least one or two 30-mL syringes of solution (equipped thesia, they are recognized as being unreliable for thatwith an 18-gauge needle) in advance. This will facilitate purpose479), drowning, or air embolism (ie, injectionrapid administration and ensure the animal does not of air into the vasculature); and electrocution with aregain consciousness. Any available vein may be used; 120-V electrical cord, drowning, and exsanguination inhowever, it is important to position oneself out of the conscious animals.reach of limbs and hooves that may cause injury duringperiods of involuntary movement. Once the needle is in S3.2.2.5 Neonatesthe vein, the injection should be delivered rapidly. Neonatal calves, lambs, and kids—Neonatal calves Magnesium sulfate may be administered similarly present special challenges for euthanasia. Methods in-to potassium chloride. Death may not occur as rapidly, clude barbiturate overdose, gunshot, and captive boltbut similar to administration of potassium chloride, (penetrating or nonpenetrating) with an adjunctiveresidue risks for predators and scavengers are low (see method applied to ensure death. Manually applied bluntNoninhaled Agents). force trauma to the head is not acceptable for calves56 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 57. because their skulls are too hard to achieve immediate tient and unconscious throughout the first 75% to 80%destruction of brain tissue leading to unconsciousness of gestation.432 As neuronal pathways between the ce-and death. Manually applied blunt force trauma is also rebral cortex and thalamus become better established,difficult if not impossible to apply consistently because the fetus develops the capacity for sentience. However,of the degree of restraint required and complications in while maintained within the protected environment ofpositioning calves, lambs, and kids for conducting this the animal’s uterus it remains in an unconscious stateprocedure. due to the presence of eight or more neuroinhibitors Barbiturate overdose may be used for euthanasia that act on the cerebral cortex of the fetus to maintain itof neonatal calves, lambs, and kids. In noncommercial in the sleep-like state of unconsciousness. At birth, thesituations, this method may be preferred over physical combined effects of reduced neuroinhibition and onsetmethods. Drawbacks include temporary animal distress of neuroactivation contribute to gradual arousal of theassociated with restraint and needle placement, chal- mammalian newborn into a state of consciousness thatlenges associated with disposal of remains (residue occurs within minutes to several hours after birth.432concerns), a requirement for DEA registration, and be- These observations indicate that the fetus does notcause the use of barbituates is extralabel for these spe- suffer as if drowning in amniotic fluid when the dam iscies, administration by or under the supervision of a euthanized; nor is it likely to experience pain associ-veterinarian. Assuming these conditions can be met, ated with other types of invasive procedures in utero.barbiturate overdose is generally less objectionable to These studies also support the rationale for internation-owners and observers than other methods. al guidelines on the handling of fetuses suggesting that Use of a penetrating or purpose-built nonpenetrat- fetuses should not be removed from the uterus beforeing captive bolt (controlled blunt force trauma) is ac- the EEG is most likely to be isoelectric. For example,ceptable with conditions for calves, lambs, and kids. when animals are euthanized by physical methods thatControlled blunt force trauma differs from manually include exsanguination, delaying removal of the fe-applied blunt force trauma because captive bolts de- tus from the uterus for a minimum of 5 minutes afterliver an appropriate and uniform amount of force each hemorrhaging has ceased generally assures a substan-time they are fired, and structural brain damage is more tial amount of anoxia-induced damage to the cerebralconsistent. Studies480 using controlled blunt force trau- cortex that will normally prevent progression towardma methods found that focal as well as diffuse injury a return to sensibility.482 If there is any doubt as to thecaused by penetrating and nonpenetrating captive bolt fetus’s level of consciousness, it should be euthanizedpistols was similar and sufficient for both to be consid- immediately by captive bolt and adjunctive methods asered as effective for euthanasia of lambs. Based on elec- appropriate.trophysiologic evidence,333 researchers determined that The unconscious state of the fetus also addressesthe primary determinant of effective shooting is the the welfare concerns of those who fear that the collec-impact of the bolt and not penetration of the bolt into tion of tissues (in particular, fetal calf blood by intracar-brain tissues. In contrast, one report481 credits struc- diac puncture) from live fetuses in the immediate post-tural changes including focal damage adjacent to the slaughter period creates undue suffering. Although thewound track and damage to peripheral tissues of the heart may continue to beat (which is necessary for thecerebrum, cerebellum, and brainstem as the predomi- successful collection of fetal blood), in the absence ofnant factors affecting the loss of respiratory function breathing there is little likelihood of return to a state ofand consciousness. consciousness.482 These are by no means insignificant Because calves’, lambs’, and kids’ skulls and cra- concerns as there is high demand for fetal tissues toniums are smaller, physical methods such as gunshot support laboratory research. A 2002 report483 suggestsand captive bolt require accurate placement and direc- that world demand for fetal calf serum was 500,000 L/ytion of the bullet or bolt to assure penetration of the and growing, a need that would require the harvest ofbrain and brainstem. The captive bolt device should at least 1,000,000 fetuses/y.be placed on the intersection of two lines each drawn The information derived from these observationsfrom the lateral canthus of the eyes to the site of horn also has application for fetal rescue situations that mayformation on the contralateral (opposite) side. Direct- involve euthanasia of late-term pregnant dams by phys-ing the bolt toward the foramen magnum increases ical methods. The reason why one might attempt thislikelihood of damaging the brainstem; but this may is to avoid remains disposal complications from drugbe difficult since this structure is a relatively small residues as would occur if the fetus were to be deliveredtarget in neonates. This highlights the reason why an by caesarian section using standard surgical methods.adjunctive method such as exsanguination, pithing, or Although respiration is interrupted, the heart continuesthe rapid IV administration of a saturated solution of to beat in animals rendered unconscious using physi-potassium chloride or magnesium sulfate is necessary cal methods. Therefore, it may be possible to rescue ain neonates. fetus from an unconscious dam by caesarian section if the procedure can be performed before the fetus suf-S3.2.2.6 Dams and Fetuses fers irreversible effects of anoxia. Once the fetus is suc- Prerequisites for the sensation of pain, distress, or cessfully delivered, euthanasia of the dam may be con-pleasurable experiences are sentience and conscious- firmed via any of the previously described adjunctiveness. Both are necessary for animals to experience ei- methods. It is important to understand that there arether positive or negative states. Behavioral and EEG significant risks to fetal welfare if rescue is attempted.evidence indicates that mammalian fetuses are insen- Welfare complications associated with fetal rescue at-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 57
  • 58. tempts would include impaired brain function caused S3.3.1.1 Acceptable Methodsby anoxia occurring during the rescue attempt, com-promised respiratory function and body heat produc- S3. Noninhaled Agentstion resulting from fetal immaturity, and greater risk of Barbiturates and barbituric acid derivatives—Ma-infection as a consequence of failure of passive transfer ture sows, boars, and grower-finisher pigs may beof immunity.432,484,485 When the value of the fetus justi- euthanized by IV administration of euthanasia solu-fies the effort to secure a successful live delivery, the tions containing barbiturates.496 A dosage of 1 mL/5 kgpreferred approach to assure fetal health and welfare (0.45 mL/2.3 lb) up to 30 kg (66 lb), then 1 mL/10 kgis by caesarian section using standard surgical proce- (0.45 mL/4.5 lb) thereafter, has been recommended.497dures. This method may not cause death if a lethal dose is not administered IV. Barbituates are not commonly used Barbiturates and barbituric acid derivatives—Pento- in field conditions, but may be applicable in some set-barbital readily crosses the placenta resulting in fetal tings. Because these drugs are controlled substancesdepression in pregnant animals. However, death of the they must be administered by personnel who are reg-dam normally precedes the death of the fetus. In one istered with the US DEA, and extralebel use requiresstudy486 cardiac arrest in lambs was delayed for as long administration by or under the supervision of a veteri-as 25 minutes beyond the death of the dam. Similar ob- narian. Strict record keeping is required of all who useservations in mice demonstrated that death of the fe- and store these drugs.tuses could only be achieved by the use of doses well Many find euthanasia by the IV administration ofin excess of those normally required for euthanasia.487 a barbituate less displeasing than gunshot, captive bolt,Based on these observations, one could offer a similar or electrocution. Therefore, it is preferred in some set-recommendation to that provided previously for death tings. A disadvantage of this method of euthanasia isby exsanguination whereby fetuses should be retained that tissues from animals euthanized with barbiturateswithin the uterus for at least 15 to 20 minutes after ma- may not be suitable for diagnostic evaluation. Further-ternal death has occurred to prevent the delivery of vi- more, options for disposal of animals euthanized withable fetuses. barbiturates are complicated by concerns for residues that create risks for scavengers and other domesticatedS3.3 SWINE animals that may consume portions of the animal’s re- Methods of euthanasia commonly applied to swine mains, and renderers may not accept animal remainsinclude CO2, Ar, N2, gas mixtures, gunshot, nonpene- contaminated with barbiturate residues.trating and penetrating captive bolts, overdose of an an-esthetic administered by a veterinarian, electrocution, S3.3.1.2 Acceptable With Conditions Methodsand blunt force trauma (in suckling piglets only). Selec-tion of the most appropriate method for each situation S3. Inhaled Agentsis dependent upon size and weight of the animal, avail- Carbon dioxide, nitrogen, and argon—Studied gasability of equipment and facilities, operator skill and mixtures include N2 with CO2; Ar, alone and withexperience with the procedure, aesthetic concerns, hu- CO2; and CO. Inhaled agents are most commonly usedman safety, and options for disposal of remains. Certain as a method of euthanasia in slaughter plants, and arephysical methods of euthanasia may require adjunctive considered to be acceptable with conditions. Inhaledmethods such as exsanguination or pithing to ensure agents have greater application for pigs weighing 70death. A brief description of each method and appro- lb or less, rather than grower-finisher pigs or maturepriate candidates for it are described. Detailed informa- sows and boars. Gas combinations (eg, CO2 and Ar)tion on inhaled, noninhaled, and physical methods of have been shown to be effective alternatives to CO2euthanasia may be found in the respective sections of alone, and when the concentration of CO2 is high,this document. duration of exposure ensures unconsciousness is fol- lowed by death. These methods are described in great-S3.3.1 Mature Sows, Boars, and er detail for the euthanasia of nursery pigs and in theGrower-Finisher Pigs section on Inhaled Agents. Methods usually used for euthanasia of sows, boars,and grower-finisher pigs include gunshot, penetrating S3. Physical Methodscaptive bolt, electrocution, and barbiturate overdose. Gunshot—Gunshot is commonly used for euthana- Use of physical methods of euthanasia requires sia of growing and adult swine. When properly con-direct contact with the animal, and therefore restraint ducted using the appropriate firearm, euthanasia byis necessary. Use of a snare is the most common form gunshot produces immediate loss of consciousness andof restraint for adult swine. Studies488–495 demonstrate rapid death. There are three possible sites for conduct-varying degrees of stress associated with restraint by ing euthanasia in swine: frontal, temporal, and from be-snaring techniques. To minimize stress associated hind the ear toward the opposite eye (Figure 12). Thewith snaring, personnel conducting euthanasia of frontal site is in the center of the forehead slightly aboveswine are advised to make advance preparations (eg, a line drawn between the eyes. The projectile should beprepare the site, load the gun or captive bolt) so that directed toward the spinal canal. The temporal site isthe time during which the animal must be restrained slightly anterior and below the ear. Specific sites mayis minimized. vary slightly according to breed.351,352,498 Because of the thickness of the pig’s skull, muzzle58 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 59. may be captured in an earthen surface. Shotguns may be used at short range and offer the advantage of less potential for bullet ricochet. Twelve-, 16- or 20-gauge shotguns are recommended for mature pigs. The muz- zle should never be held flush to the skull. Gunshot is an effective, low-cost method of eutha- nasia when properly performed. Firearms are readily available in most areas. Human safety is the primary concern with the use of gunshot for euthanasia. Proper training on firearm safety and use is imperative and gunshot should only be performed by personnel who have had appropriate training. Penetrating captive bolt—Use of well-maintained penetrating captive bolt guns with ammunition appro- priately selected for the size of the animal is acceptable with conditions as a method of euthanasia for growing and adult swine.499,500 Proper application of the pen- etrating captive bolt requires restraint of the animal because the device must be held firmly against the fore- head over the site described for gunshot (Figure 12). When performed correctly, the pig drops to the floor immediately, exhibiting varying amounts of tonic and clonic muscle movements. Confirmation that the ani- mal has been rendered insensible includes observation of the following: rhythmic breathing stops, no righting reflex is observed, vocalization is absent, and no palpe- bral reflexes or responses to noxious stimuli are pres- ent. All pigs should be observed for evidence of these responses until death has been confirmed. Death following use of the penetrating captive bolt is commonly achieved, but is not assured depend- ing upon bolt length and depth of the frontal sinus in mature sows and boars. Therefore, secondary steps to ensure death (eg, a second application of the penetrat- ing captive bolt, exsanguination, pithing) should be ap- plied as necessary. Breed differences result in variable skull shapes making determination of the best anatom- ic site for conducting euthanasia in mature sows and boars difficult.352 Penetrating captive bolts offer safety advantages compared with firearms. Properly applied, the method is very effective and costs associated with its use are minimal. However, it is important that penetrating cap- tive bolt guns be maintained regularly (cleaning andFigure 12—There are three possible sites for conducting eutha-nasia in swine: frontal, temporal and from behind the ear toward replacement of worn parts) and that cartridge chargesthe opposite eye. The frontal site is in the center of the forehead be stored properly to ensure appropriate bolt velocity.slightly above a line drawn between the eyes. The bolt or bullet Bolt length and ammunition requirements for effectiveshould be directed toward the spinal canal. The temporal site is single-step euthanasia vary for different sizes and ma-slightly anterior and below the ear. The ideal target location anddirection of aim may vary slightly according to breed and the age turities of pigs. Using a captive bolt of inappropriateof the animal (due to growth of the frontal sinuses). (Adapted length or with insufficient charge reduces effectiveness.with permission from Shearer JK, Nicoletti P Anatomical land- . Personnel must be trained in the proper use of pen-marks. Available at: www.vetmed.iastate.edu/vdpam/extension/dairy/programs/humane-euthanasia/anatomical-landmarks. etrating captive bolts to ensure effective euthanasia.Accessed Jun 24, 2011.) Electrocution—Electrocution as a sole method of eu-energies of 300 ft-lb or more are required for euthanasia thanasia can achieve death via 2-step or single-step pro-of adult sows, boars, and growing-finishing pigs. When cesses.359,373,501–508 Electrical current must pass throughthe alternate site behind the ear is chosen, a .22 caliber the brain to achieve loss of consciousness, but then mustfirearm loaded with a solid-point bullet may be used. cross the heart to cause fibrillation and cardiac arrest. AsWadcutters and fragmenting bullets should not be used a 2-step process, electrode placements are head-head,for euthanasia of adult swine. Potential for ricochet is followed by head to flank, for the appropriate time. For areduced when euthanasia by gunshot can be conducted single-step process for euthanasia, head to opposite flankoutdoors where bullets that pass through the animal is an example of appropriate placement.AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 59
  • 60. Head-only electrocution induces a grand mal sei- euthanasia solutions containing barbiturates. Becausezure and immediate unconsciousness, but death does these drugs are controlled substances they must be ad-not occur unless followed by head-to-heart electrocu- ministered by personnel who are registered with the UStion or the application of an adjunctive method to en- DEA. Strict record keeping is required of all who usesure death such as exsanguination373,509 or pithing. The and store these drugs.secondary step, whether head-to-heart electrocution or Many find euthanasia by the IV administration ofanother method, must be performed within 15 seconds an anesthetic less aesthetically displeasing than admin-of onset of unconsciousness; otherwise, the animal may istration of CO2, captive bolt, or electrocution. There-regain consciousness. Head-only electrocution is per- fore, it is preferred in some settings. A disadvantage offormed by placement of the electrodes in one of three this method is that tissues from animals euthanized withpositions: between the eyes and base of the ears on either barbiturates may not be suitable for diagnostic evalua-side of the head; below the base of the ears on either side tion and cannot be used for food. Furthermore, optionsof the head; or diagonally, below one ear to above the for disposal of animals euthanized with barbiturates areopposite eye. Placement of electrodes for head-to-heart complicated by concerns for residues that create riskselectrocution is on the head in front of the brain (some for scavengers and other domesticated animals thatuse the base of the ear) with a secondary electrode at- may consume portions of the animal’s remains.tached to the body behind the heart on the opposite side.This assures diagonal movement of current through the S3.3.2.2 Acceptable With Conditions Methodsanimal’s body. With specific electrode placement, currentof 110 V at a minimum frequency of 60 Hz applied for S3. Inhaled Agentsa minimum of 3 seconds is sufficient for euthanasia of Carbon dioxide—Carbon dioxide alone or in com-pigs up to 125 kg.510 Systems used for electrocution must bination with N2 or Ar has been used successfully forbe capable of meeting minimum current requirements to euthanasia.206,208,212,250,252,511 Properly applied, inhalationensure insensibility in the head-only method, and insen- of CO2 is an effective method of euthanasia. On thesibility and cardiac fibrillation in the head-heart method. other hand, if air exchange rates are not carefully con- Electrocution is effective as a single-step process trolled and monitored, animals may suffer substantialwith appropriate tong or clamp placement. However, stress from suffocation prior to loss of consciousnessproper training and special equipment must be used to and death (see Inhaled Agents section of Guidelines).ensure adequate and safe euthanasia. While electrocu- Conducting this procedure on small pigs requirestion is commonly used to render animals insensible in a container large enough for the size and number ofslaughter plants and safety precautions in that environ- pigs to be euthanized. Pigs may be exposed to CO2 byment are routine, for implementation on-farm where use gradually displacing ambient gases (introducing CO2of the method is less common, extra precautions may into the container) or by introducing the animals into aneed to be taken to ensure human safety. Agonal gasping prefilled environment. In the gradual-fill approach, pigsmay be evident after current is withdrawn and may be are placed in an enclosed container and CO2 flow is ini-aesthetically unacceptable for observers and operators. tiated at a rate and for a time to reach a level sufficient to achieve euthanasia. In the prefill approach, a concen-S3.3.1.3 Adjunctive Methods trated environment of CO2 is created, pigs are placed in Exsanguination—While not appropriate as a sole that environment, and CO2 flow is resumed to maintainmethod of euthanasia, exsanguination may be performed effective euthanasia concentrations. In both methods,as a secondary step to ensure death when necessary. exposure of pigs with normal respiration to a constant supply of 80% to 90% CO2 for a minimum of 5 minutes Pithing—While not appropriate as a sole method of is necessary for effective euthanasia.211,214,251,512–518euthanasia, pithing may be performed as a secondary Carbon dioxide offers advantages for euthanasia,step to ensure death when necessary. including that it is relatively inexpensive, nonflam- More information about these methods is available mable and nonexplosive, and clean (no blood loss).in the Physical Methods section of the Guidelines. Drawbacks to the use of CO2 are that it requires special equipment and training for efficient and safe applica-S3.3.2 Nursery Pigs (70 lb or Lighter) tion, and that there is little published research on ap- Nursery pigs may be euthanized by use of CO, propriate techniques for euthanizing young (neonatalCO2, gunshot, penetrating captive bolt, purpose-built and growing) pigs. Systems must be able to achieve anonpenetrating captive bolt, electrocution, or anes- level of anesthesia while not causing hypothermia. Anthetic overdose. Descriptions of the use of CO2 and appropriate pressure-reducing regulator and flow meternonpenetrating captive bolt for euthanasia of young capable of generating the recommended displacementpigs follow. For details on other methods please see the rates for the size container being utilized is absolutelypreceding information in this section or the Physical necessary. Death must be verified following administra-Methods section of the Guidelines. tion of CO2. This can be done by examination of in- dividual animals or adherence to validated exposureS3.3.2.1 Acceptable Methods processes proven to result in death.352 If an animal is not dead, exposure must be repeated or followed withS3. Noninhaled Agents another method of euthanasia. Bartiburates and barbituric acid derivatives—Nurs- For young pigs, movement during the inductionery pigs may be euthanized by IV administration of phase has caused some to question the degree of stress60 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 61. that may be induced with this method. Some interpret Many find euthanasia by the IV administration ofthese movements as indications of aversion. While this an anesthetic less displeasing than administration ofmay be the case in systems that are not functioning prop- CO2, captive bolt, manually applied blunt force trauma,erly, there is evidence that such reactions may be normal or electrocution. Therefore, it is preferred in some set-for pigs in an unconscious state.214,515,516 Small or inca- tings. A disadvantage of this method is that tissues frompacitated piglets have low tidal volumes and will not die animals euthanized with barbiturates may not be suit-as rapidly as larger, more viable pigs. Carbon dioxide able for diagnostic evaluation. Furthermore, optionseuthanasia in chamber settings has not been extensively for disposal of animals euthanized with barbituratesstudied for larger pigs. Meyer and Morrow148 recommend are complicated by concerns about residues that cre-that chamber volume be exchanged at least 2.5 times to ate risks for scavengers and other domesticated animalsaccommodate the wash-in–washout principle regard- that may consume portions of the animal’s remainsless of the size of swine to be euthanized. Monitoring ofequipment and gas must be routine and consistent to en- S3.3.3.2 Acceptable With Conditions Methodssure there is always sufficient gas to accomplish the ob-jective of euthanasia. Carbon dioxide containers should S3. Inhaled Agentsnever be placed in an unventilated area due to risks as- Carbon dioxide—Carbon dioxide may be effectivesociated with an overdose of gaseous CO2 for humans. as a method of euthanasia for small groups of neonatal piglets; however, the parameters of the technique needS3. Physical Methods to be optimized and published to ensure consistency Nonpenetrating captive bolt—A purpose-built non- and repeatability. In particular, the needs of piglets withpenetrating captive bolt may be used for euthanasia of low tidal volumes must be explored.young pigs. The concussive impact of the bolt inducesan immediate loss of consciousness that when followed S3. Physical Methodsby an adjunctive method to ensure death meets the cri- Nonpenetrating captive bolt—The purpose-builtteria for euthanasia. The nonpenetrating captive bolt nonpenetrating captive bolt can be an effective methodworks best in younger pigs before the frontal bones are of euthanasia for young piglets.519–521 Loss of conscious-fully developed and hardened. ness and death are caused by a severe nonpenetrating Use of a proper functioning nonpenetrating captive concussive force applied to the forehead of the piglet.bolt with appropriate charges offers the advantage of The utility of the nonpenetrating captive bolt is focuseddelivering a uniform concussive force to the skull (con- on the unique condition in suckling and young pigstrolled blunt force trauma). This reduces the potential where the frontal bones are not fully developed, leav-for ineffective stunning and euthanasia that may occur ing the brain susceptible to blunt, high-velocity impact.more often with the use of manually applied blunt force When used in appropriately sized and aged pigstrauma. However, this method requires immediate ap- a secondary step to ensure death is unnecessary. Useplication of an adjunctive method to ensure euthanasia. of the nonpenetrating captive bolt (controlled blunt force trauma) is currently being studied with positive Electrocution—Electrocution is acceptable with results for use in young swine. The nonpenetrating cap-conditions for swine weighing more than 10 lb. Details tive bolt can be powered pneumatically or through theare provided earlier in this section and in the Physical use of appropriate ammunition. Some brands of captiveMethods section of the Guidelines. bolt guns have been made versatile by providing dif- ferent heads (varying length of bolt and penetrating orS3.3.3 Suckling Pigs nonpenetrating end), and ammunition for various-size Options for the euthanasia of suckling pigs include pigs, which allows the same gun to be used in differentCO2; Ar, N2 and CO2 mixtures; CO; inhaled anesthet- situations. Current research indicates that euthanasiaics; purpose-built nonpenetrating captive bolt; electro- using a nonpenetrating captive bolt is effective assum-cution (for pigs over 10 lb); anesthetic overdose; and ing sufficient power afforded by gun design and the useblunt force trauma. Described are the application of of appropriate ammunition.519,520barbituates, nonpenetrating captive bolt, manually ap-plied blunt force trauma, and CO2. See previous sec- Manually applied blunt force trauma—Manually ap-tions of the Guidelines for more detailed information plied blunt force trauma, when performed correctly,on the application of other euthanasia techniques. meets the definition of euthanasia, namely causing min- imal distress with rapid loss of consciousness leading toS3.3.3.1 Acceptable Methods death. As for the nonpenetrating captive bolt, the utility of manually applied blunt force trauma is based on theS3. Injectable Agents unique condition in suckling and young pigs where the Bartiburates and barbituric acid derivatives—Suck- frontal bones are not fully developed, leaving the brainling pigs may be euthanized by IV administration of susceptible to blunt, high-velocity impact. This methodeuthanasia solutions containing barbiturates. Because is less aesthetically acceptable than other alternatives,these drugs are controlled substances they must be ad- but when properly performed, death is rapid. Uncer-ministered by personnel who are registered with the US tainty of success often causes repeated application orDEA, and extralabel use requires administration by or selection of an alternative euthanasia method.520 Theunder the supervision of a veterinarian. Strict record AVMA encourages those using manually applied bluntkeeping is required of all who use and store these drugs. force trauma to the head as a euthanasia method to ac-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 61
  • 62. tively search for alternatives to ensure that criteria for sponses, times to collapse, unconsciousness, death,euthanasia can be consistently met. loss of somatosensory evoked potentials, loss of visu- ally evoked responses, and changes in EEG and ECGS3.4 POULTRY (see Inhaled Agents section of the Guidelines). Carbon Euthanasia methods for poultry (domesticated dioxide has successfully been applied for euthanasiabirds used for egg, meat, or feather production [eg, of nonhatched eggs (pips), newly hatched poultry inchickens, turkeys, quail, pheasants, ducks, geese]) in- hatcheries, and adult birds (including routine eutha-clude gas inhalation, manually applied blunt force trau- nasia of large commercial laying hen flocks356,522) andma, cervical dislocation, decapitation, electrocution, on farms keeping birds for research or elite genetics.gunshot, captive bolt, and injectable agents. Where ap- Because neonatal birds may be more accustomed topropriate, additional comments are included to address high concentrations of CO2 (incubation environmentsphysiologic differences among avian species, variations typically include more CO2), concentrations necessaryin environment, and the size or age of birds. to achieve rapid euthanasia of pipped eggs or newly hatched chicks may be substantially greater (as high asS3.4.1 Acceptable Methods 80% to 90%) than for adults of the same species. Carbon dioxide may invoke involuntary (uncon-S3.4.1.1 Noninhaled Agents scious) motor activity in birds, such as flapping of the Overdoses of injectable anesthetics, including barbi- wings or other terminal movements, which can damageturates and barbituric acid derivatives—Poultry may be tissues and be disconcerting for observers.248,270 Slowereuthanized by IV injection of overdoses of anesthetics, induction of euthanasia in hypercapnic atmospheresincluding barbiturate and barbituric acid derivatives. reduces the severity of convulsions after loss of con-Because these drugs are controlled substances they sciousness.204,205 Death normally occurs within min-must be administered by personnel who are registered utes, depending on the species and the concentrationwith the US DEA, and extralabel use requires adminis- of CO2 present in the closed chamber.tration by or under the supervision of a veterinarian.Strict record keeping is required of all who use and Carbon monoxide—Carbon monoxide may also bestore these drugs. used for euthanasia of poultry. More convulsions may Many find administration of an anesthetic less dis- be observed in the presence of CO than normally oc-pleasing than administration of CO2, CO, captive bolt, cur when CO2 is used for euthanasia.188 The CO flowmanually applied blunt force trauma, cervical disloca- rate should be sufficient to rapidly achieve a uniformtion, decapitation, or electrocution. Therefore, it may be concentration of at least 6% after birds are placed inpreferred in some settings. A disadvantage of this method the chamber (see Inhaled Agents section). Only pure,is that tissues from animals euthanized with barbiturates commercially available CO should be used. The directmay not be used for food and may not be suitable for application of products of combustion or sublimationdiagnostic evaluation. Furthermore, options for disposal is not acceptable due to unreliable or undesirable com-of animals euthanized with barbiturates are complicated position and or displacement rate. Appropriate precau-by concerns for residues that create risks for scavengers, tions must be taken to ensure human safety because COother domesticated animals that may consume portions has a cumulative effect in binding hemoglobin.of the animal’s remains, and humans. Nitrogen or argon—Nitrogen or Ar, mixed or usedS3.4.2 Acceptable With Conditions Methods alone, with approximately 30% CO2 is acceptable with conditions for euthanasia of poultry provided the re-S3.4.2.1 Inhaled Agents sidual atmospheric O2 level can be reduced to and held Inhaled gases may be used satisfactorily for eutha- at sufficiently low levels (eg, 2% to 3%).267,523 Thesenasia of poultry, and detailed information about the agents tend to cause more convulsions (eg, wing flap-various types of inhaled gases is available in the In- ping) than CO2 in air (see Inhaled Agents section ofhaled Agents section of the Guidelines. When inhaled the Guidelines).204,269 It has also been noted that con-gases are used for euthanasia, birds should be checked vulsions may start when consciousness, at least to someto verify death because they may appear dead but can degree, may still be a possibility.256,524regain consciousness if the exposure time or the con-centration of the agent is insufficient. Gases must be S3.4.2.2 Physical Methodssupplied in purified forms without contaminants or The following methods are acceptable with conditionsadulterants, typically from a commercially supplied cyl- for euthanasia of poultry. Euthanasia methods should beinder or tank. The gas-dispensing system should have chosen based on the welfare of the bird, human safety, skillsufficient capacity and control to maintain the neces- and training of personnel, availability of equipment, andsary gas concentrations in the container being utilized, the ability to adequately restrain the bird.and the container itself should be sufficiently airtight tohold the gas at appropriate levels. Cervical dislocation—When performed on con- scious poultry, cervical dislocation must result in luxa- Carbon dioxide—The most common gas used for tion of the cervical vertebrae without primary crushingeuthanasia of poultry is CO2, and its application has of the vertebrae and spinal cord. Manual or mechanicalbeen extensively studied for chickens, turkeys, and cervical dislocation may be used for poultry of an ap-ducks with information available about behavioral re- propriate size and species when performed by compe-62 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 63. tent personnel who correctly apply the technique. In to administer these agents to a bird that is fully anes-some classes of poultry there is evidence that cervical thetized or otherwise unconscious as a means to ensuredislocation may not cause immediate unconscious- death.ness.337–339,354 The legs of the bird should be grasped (orwings if grasped at the base) and the neck stretched by Exsanguination—Although exsanguination of apulling on the head while applying a ventrodorsal rota- conscious bird is an unacceptable method of euthana-tional force to the skull. Crushing of cervical vertebrae sia, it is acceptable to exsanguinate birds that are fullyand spinal cord is not acceptable unless the bird is first anesthetized or otherwise unconscious as a means torendered unconscious. ensure death. Biosecurity precautions during and fol- lowing exsanguination should be observed as part of Decapitation—Decapitation is acceptable with con- appropriate disease control.ditions for the euthanasia of poultry when performedby competent personnel. Decapitation should be ex- S3.4.4 Embryos and Neonatesecuted with a sharp instrument, ensuring rapid and un- In addition to methods involving inhaled agentsobstructed severing of the head from the neck. Use of a mentioned previously, the following methods are ac-bleeding cone may facilitate restraint. ceptable with conditions for euthanasia of embryos or neonates. Manually applied blunt force trauma—Euthanasia Embryonated eggs may be destroyed by prolongedby manually applied blunt force trauma to the head exposure (20 minutes) to CO2, cooling (4 hours atis acceptable with conditions for turkeys or broiler 40°F), or freezing.52 In some cases inhaled anestheticsbreeder birds that are too large for cervical dislocation. can be administered through the air cell at the large endManually applied blunt force trauma must be correctly of the egg. Egg addling can also be used.416 Embryos inapplied by competent personnel. Operator fatigue can eggs that may have been opened may be decapitated.lead to inconsistency in application, creating concern Maceration, via use of a specially designed mechan-that the technique may be difficult to apply humanely ical apparatus having rotating blades or projections,to large numbers of birds. For this reason, the AVMA causes immediate fragmentation and death of newlyencourages those using manually applied blunt force hatched poultry and embryonated eggs.271 A review bytrauma to the head as a euthanasia method to search the American Association of Avian Pathologists406 of thefor alternatives. use of commercially available macerators for euthanasia of chicks, poults, and pipped eggs indicates that death Electrocution—Electrocution is acceptable with by maceration in poultry up to 72 hours old occursconditions for euthanasia of individual birds. Birds immediately with minimal pain and distress. Macera-subjected to electrocution should be observed to ensure tion is an alternative to the use of CO2 for euthanasia ofdeath or an adjunctive method, such as exsanguination poultry up to 72 hours old. Maceration is believed to beor cervical dislocation, should be performed immedi- equivalent to cervical dislocation and cranial compres-ately afterwards to ensure death. A small percentage of sion as to time to death, and is considered to be an ac-birds do not develop ventricular fibrillation even when ceptable means of euthanasia for newly hatched poul-exposed to high amperage current. try by the Federation of Animal Science Societies,407 Agriculture Canada,408 World Organisation for Animal Gunshot—Gunshot is acceptable with conditions Health,342 and European Council.525for free-ranging poultry and ratites when capture or re- Maceration requires special equipment that muststraint would potentially be highly stressful for the ani- be kept in excellent working order. Newly hatchedmal or dangerous for humans. Gunshot is not recom- poultry must be delivered to the macerator in a way andmended for captive poultry where restraint is feasible. at a rate that prevents a backlog at the point of entry into the macerator and without causing injury, suffoca- Penetrating and nonpenetrating captive bolt—Cap- tion, or avoidable distress before maceration.tive bolts (penetrating or nonpenetrating) are acceptablewith conditions for euthanasia of large poultry (turkeys,broiler breeders, ratites, waterfowl, etc) when performed S4. EQUIDSby competent personnel. The captive bolt pistol must be Methods acceptable with conditions are equivalentused in accordance with the manufacturer’s recommen- to acceptable methods when all criteria for applicationdations and the bird should be appropriately restrained of a method are met.to avoid injury to personnel. Birds should be observedfollowing captive bolt administration to ensure that S4.1 GENERAL CONSIDERATIONSdeath occurs. Any bird showing signs of recovery mustreceive a second shot or be killed by some other means S4.1.1 Human Safetythat is acceptable for a conscious bird. When equids are euthanized, consideration should be given to the unpredictability of a falling or thrashingS3.4.3 Adjunctive Methods equid. Most methods of euthanasia will result in some Potassium chloride or magnesium sulfate—Although degree of exaggerated muscular activity after the equidIV or intracardiac administration of potassium chlo- falls even if the equid is not experiencing pain or dis-ride or magnesium sulfate to a conscious bird as a sole tress. Whatever euthanasia method is used should notmethod of euthanasia is unacceptable, it is acceptable put personnel at unnecessary risk.AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 63
  • 64. S4.1.2 Disposal of Remains For equids euthanized with pentobarbital, disposalof remains must be carried out promptly through com-mercial rendering, on-farm burial, incineration or cre-mation, direct haul to a solid waste landfill, or biodiges-tion. This will help prevent exposure of wildlife and do-mestic animals to potentially toxic barbiturate residues.Disposal of remains must be conducted in accord withall federal, state, and local regulations.S4.2 METHODSS4.2.1 Acceptable MethodsS4.2.1.1 Noninhaled agents Barbiturates or barbituric acid derivatives—Pento-barbital or a pentobarbital combination is the princi-pal choice for equine euthanasia by chemical means.Because a large volume of solution must be injected,use of an IV catheter placed in the jugular vein will fa-cilitate the procedure. To facilitate catheterization ofan excitable or fractious equid, a tranquilizer, such asacepromazine, or an α2-adrenergic receptor agonist canbe administered, but these drugs may prolong time toloss of consciousness because of their effect on circu-lation and may result in varying degrees of muscularactivity and agonal gasping. Opioid agonists or agonist-antagonists in conjunction with α2-adrenergic receptoragonists may further facilitate restraint.S4.2.2 Acceptable With Conditions MethodsS4.2.2.1 Physical Methods Penetrating captive bolt and gunshot—Penetratingcaptive bolt and gunshot are considered acceptable withconditions for euthanasia of equids. Both should onlybe used by well-trained personnel who are regularlymonitored to ensure proficiency, and firearms must bewell maintained. Appropriate restraint is required forapplication of the penetrating captive bolt and specialcare should be taken to ensure that personnel are notinjured by ricochet from free bullets. The correct anatomic site for application of gun-shot and penetrating captive bolt is illustrated in Figure13.526 The site for entry of the projectile is describedas being on the intersection of two diagonal lines eachrunning from the outer corner of the eye to the base ofthe opposite ear.S4.2.3 Adjunctive Methods Potassium chloride—Although unacceptable whenused in unanesthetized equids, the use of a saturatedsolution of potassium chloride injected IV or intracar-dially in an equid in a deep surgical plane of generalanesthesia is an acceptable method to invoke cardiacarrest and death.S4.2.4 Unacceptable Methods Figure 13—Anatomic site for the application of gunshot or pen- etrating captive bolt for euthanasia of equids. The point of entry Chloral hydrate—Chloral hydrate has an almost of the projectile should be at the intersection of two imaginaryimmediate sedative action, but unless it is combined lines, each drawn from the outside corner of the eye to the cen-with other anesthetics, onset of anesthesia is delayed. ter of the base of the opposite ear. (Adapted with permission from Shearer JK, Nicoletti P Anatomical landmarks. Available at: .Associated adverse effects can be severe and aestheti- www.vetmed.iastate.edu/vdpam/extension/dairy/programs/hu-cally objectionable, and chloral hydrate also has limited mane-euthanasia/anatomical-landmarks. Accessed Jun 24, 2011.)64 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 65. availability. For these reasons, chloral hydrate is an un- and abdominal cavities. When giving intracoelomic in-acceptable means of euthanizing equids. jections care must be taken that material is not injected into the air sacs, which could potentially drown the birdS4.3 SPECIAL CASES AND EXCEPTIONS or expose its respiratory system to irritating substances. In emergency situations, such as euthanasia of an Air sacs act as a bellows to ventilate birds’ small, nonex-equid with a serious injury at a racetrack or another panding lungs.534 Because there is no diaphragm, birdsequestrian event, it may be difficult to restrain a dan- need to be able to move their sternum ventrally andgerous equid for IV injection. While administration of cranially to breathe.535 Birds also have hollow, pneu-a sedative might be desirable, in some situations it is matic bones, such as the humerus and femur, whichpossible the equid could injure itself or bystanders be- communicate directly with the respiratory system. Pre-fore a sedative could take effect. In such cases, a neu- euthanasia and euthanasia drugs should not be admin-romuscular blocking agent (eg, succinylcholine) may istered via the intraosseous route into the humerus orbe administered to the equid IM or IV, but the equid femur because drowning or irritation to the respiratorymust be euthanized via an appropriate method as soon system may occur. Intraosseous catheters can, however,as the equid can be controlled. Succinylcholine alone be safely placed in birds, preferably in the distal ulna oror without sufficient anesthetic is not acceptable for proximal tibiotarsus.euthanasia. A bird’s respiratory system has greater capacity to process air than a mammal’s due to a unique unidirec-S5. AVIANS tional flow of air through the lungs (which prevents Methods acceptable with conditions are equivalent mixing of inspired and expired air), more efficient gasto acceptable methods when all criteria for application exchange, and a greater surface area over which O2 canof a method are met. be exchanged (more and smaller air capillaries [3 µm] than the smallest mammalian alveoli [35 µm]).535 Be-S5.1 GENERAL CONSIDERATIONS cause of their greater capacity to process air, birds are The following comments and recommendations more sensitive than mammals to inspired toxicants (eg,pertain to pet, aviary, falconry, racing, research, and zoo the proverbial canary in the coal mine collapsing beforebirds. Information about appropriate euthanasia meth- humans detect the methane in the air).536ods for wild birds can be found in the Captive and Free-Ranging Nondomestic Animals section of the Guide- S5.1.2 Restraintlines, whereas euthanasia of poultry and other birds Manual restraint for administering pre-euthana-used for food is addressed in the Animals Farmed for sia or euthanasia drugs is possible for many bird spe-Food and Fiber section. cies. Nets or other equipment may be required or may Few peer-reviewed reports are available in the sci- improve conditions for both birds and people whenentific literature about euthanasia of individual or small handling birds less acclimated to human contact (eg,groups of birds. The information that does exist com- birds in zoos, wild birds). Multiple personnel may beprises anecdotal accounts in book chapters, guidelines required to safely handle larger species, such as ratites,from various associations, and journal roundtable dis- and at least one additional person should be available tocussions and editorials.63,265,270,413,414,511,527–530 There are assist in case of an emergency. Chemical restraint mayscientific studies337,354,524,531–533 comparing various meth- be useful in some situations, particularly for dangerousods for depopulation of commercial poultry, but these birds where human safety may be compromised by ef-methods may or may not meet the criteria for eutha- forts at manual restraint. Drugs used for chemical re-nasia, and may or may not be applicable to individual straint that are administered at high doses may serve asbirds or small groups of birds. the first step of a 2-step euthanasia process. Because this taxa comprises more than 8,000 spe-cies, the choice of euthanasia method for a particular S5.2 METHODSbird will depend greatly on its species, size, anatomic Individual birds in a clinical or research settingand physiologic characteristics, environment, degree can best be rendered unconscious by use of an inhaledof domestication, clinical state, and anticipated and agent (eg, isoflurane, sevoflurane, or halothane), prioractual response to restraint. Personnel performing eu- to IV administration of an acceptable injectable eutha-thanasia should be familiar with the species being eu- nasia agent (eg, sodium pentobarbital). The followingthanized, be able to interpret avian behavior indicative methods are considered to be acceptable or acceptableof stress, and use their knowledge and experience to with conditions for avian species. For more detailed,choose restraint and euthanasia options that alleviate non–species-specific information on various agentsor minimize distress and result in rapid death. Legal and methods, please refer to the Inhaled Agents, Non-requirements may apply in cases involving endangered inhaled Pharmaceutical Agents, and Physical Methodsor migratory species. sections of the Guidelines.S5.1.1 Anatomy and Physiology S5.2.1 Acceptable Methods Birds differ anatomically and physiologically frommammals and these differences will affect whether and S5.2.1.1 Noninhaled Agentshow particular euthanasia methods may be acceptably Intravenous injection of an injectable euthanasiaapplied. Because birds lack a diaphragm, they have a agent is the quickest and most reliable means of eutha-single coelomic cavity, rather than separate thoracic nizing birds when it can be performed without causingAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 65
  • 66. fear or distress. Wild, fearful, or excited birds may re- but increase time of exposure. Field applications ofquire a sedative or anesthesia before IV injection can be CO2 for broilers have resulted in stress levels similarperformed. When IV injection is impossible, injectable to that invoked via routine handling537 or stress andeuthanasia agents can be administered via intracoelo- distress similar to the handling or restraint requiredmic, intracardiac, or intraosseous routes only if a bird for other methods of euthanasia.533 In a recent study,is unconscious or anesthetized. If the intracoelomic most turkeys would voluntarily enter a feeding cham-route is used for birds, injection into the air sacs must ber filled with Ar (90%), or a mixture of Ar (60%) andbe avoided, because of the potential for respiratory CO2 (30%), compared with only 50% of turkeys thatcompromise, irritation of the respiratory system, and would voluntarily enter the chamber when filled withdelayed absorption via the air sacs. Euthanasia agents a high concentration of CO2 (72%) alone, suggestingshould also not be administered via the intraosseous an aversion to 72% CO2.196 More research is needed toroute into the humerus or femur because of the poten- better understand this comparative aversion in turkeystial for drowning or irritation to the respiratory system. (eg, whether it is dose or species dependent and avail-Regardless of the route of administration, injectable ability of agent).agents can precipitate in tissues and can induce artifacts Concepts regarding the use of CO2 in mammals asat necropsy and on histopathologic examination.270,528 described in the Inhaled Agents section of the Guide- Barbiturates and barbituric acid derivatives can be lines generally also apply to birds. Exposure to CO2administered IV for euthanasia of anesthetized or prop- may cause involuntary (unconscious) motor activity,erly restrained unanesthetized birds. Barbiturates com- such as flapping of the wings, which can damage tis-monly used for injection are available as sodium salts sues and be disconcerting to, and potentially dangerousthat are alkaline and may be irritating and painful when for, observers.248,270injected directly into tissues, rather than IV. Therefore, There are some special considerations for the usewhen IV injection is impossible, injectable euthanasia of CO2 for euthanasia of birds. Neonatal birds may beagents can be administered via intracoelomic, intra- more acclimated to high CO2 concentrations, becausecardiac, or intraosseous routes only if a bird is uncon- the unhatched bird’s environment typically has a highscious, or anesthetized. Concepts regarding barbiturate CO2 concentration (as high as 14% in the embryonicuse in mammals generally also apply to birds and more chicken). Consequently, CO2 concentrations requiredinformation is available in the Noninhaled Agents sec- to achieve euthanasia of newly hatched chicks may betion of the Guidelines. much higher (as much as 80% to 90%) than those for adults of the same species.416,533 Diving birds also haveS5.2.2 Acceptable With Conditions Methods physiologic adaptations to hypercapnia and may re- quire higher CO2 concentrations for euthanasia.S5.2.2.1 Inhaled Agents Inhaled anesthetics—Inhaled anesthetics may be Carbon monoxide—Concepts regarding the use ofused at high concentrations as a sole method of eutha- CO for euthanasia of mammals also apply to birds. Seenasia or may be used to render birds unconscious prior the Inhaled Agents section of the Guidelines for details.to application of other methods of euthanasia.265,416 Ex-posure to high concentrations of inhaled anesthetics Nitrogen and argon—Inert gases such as N2 and(eg, halothane, isoflurane, sevoflurane, with or without Ar, and gas mixtures involving these gases (includingN2O) is acceptable with conditions for euthanasia for mixtures with CO2), have been used for euthanasia ofbirds. Birds exposed to high concentrations of inhaled poultry,538 but are not recommended for euthanasia ofanesthetic gases lose consciousness rapidly. Euthanasia companion birds.via inhaled gases may be more practical than use of an Behavioral responses of broiler chickens were ex-injectable agent if large numbers of birds, such as in amined during short (10 seconds) exposures to 100%flock or aviary situations, must be euthanized. Eutha- Ar, 100% N2, or mixtures (80% Ar / 20% N2 and 80%nasia by exposure to gas anesthetics also induces mini- N2 / 20% Ar). Normal feeding and no aversive behav-mal tissue damage and results in the least amount of iors were observed.203 Birds appear to not have intra-tissue artifact for necropsy.270,528 pulmonary chemoreceptors for N2 and Ar, and this may account for a lack of aversion during their initial ex- Carbon dioxide—High (> 40%) concentrations of posure to and hypoxia from these gases.538 As a eutha-CO2 induce anesthesia initially followed by loss of con- nasia agent, Ar gas mixed with < 2% O2 was shown tosciousness. Euthanasia via exposure to CO2 has been induce rapid loss of posture (average, 11 seconds), con-described for individual birds and small groups,265 and vulsions (average, 22 seconds), unconsciousness, andits application to euthanasia of chickens, turkeys, and death (isoelectric EEG in 1 minute).198 Convulsionsducks has been studied extensively, resulting in infor- can occur during euthanasia with these inert gases, butmation regarding times to collapse, unconsciousness, because these signs occurred after collapse and loss ofand death; loss of somatosensory evoked potentials; consciousness, these gases are considered to be humaneloss of visually evoked responses; and changes in EEG for the birds involved.538and ECG.255,531–533 Application rate of CO2 needs to bebalanced with situational needs as rapid increases in S5.2.2.2 Physical MethodsCO2 concentration decrease the amount of time to loss Physical methods of euthanasia may be necessaryof posture and consciousness, while slower increases in some field situations if other methods of euthanasiain concentration may cause less aversion or reaction, are impractical or impossible to implement. That said,66 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 67. there is little scientific information available regarding sia, potassium chloride may be administered via the IVthe effect of various physical methods on electrical ac- or intracardiac routes if a bird is unconscious or com-tivity in the brain of birds, which makes evaluation of pletely anesthetized prior to the injection.the humaneness of these procedures difficult. Cervical dislocation—Cervical dislocation has gen- Exsanguination—Although exsanguination of aerally been used for small birds (< 200 g) when no conscious, unanesthetized bird is an unacceptable ap-other method is available, but the procedure has been proach to euthanasia, exsanguination may be used forperformed on birds as large as 2.3 kg (5.1 lb). It should euthanasia of unconscious or anesthetized birds. Thisonly be performed by well-trained personnel who are approach may be appropriate if blood samples are need-regularly monitored to ensure proficiency. Skilled in- ed for diagnostic or research purposes.dividuals have been able to humanely perform cervicaldislocation in poultry. There is limited research spe- Thoracic compression—Although thoracic com-cific to birds concerning electrical activity in the brain pression of a conscious, unanesthetized bird is an unac-following cervical dislocation. Cervical dislocation of ceptable approach to euthanasia, it may be used as anchickens (average weight of 2.3 kg) did not result in adjunctive method for animals that are insentient.loss of visually evoked responses in 90% of cases whencompared with use of a percussion bolt pistol, suggest- S5.2.4 Unacceptable Methodsing that fewer than 10% of cervical dislocations re- Thoracic (cardiopulmonary, cardiac) compressionsulted in concussion.354 In 3-week-old turkeys (average is a method that has been used by biologists to terminateweight of 1.6 kg [3.5 lb]) time to insensibility (based the lives of wild, small mammals and birds mainly un-on nictitating membrane movement) was longer, but der field conditions when other methods are not avail-time to death (based on cessation of movement) was able. Although thoracic compression has been used ex-shorter after cervical dislocation compared with use of tensively in the field, data supporting this method, in-a nonpenetrating captive bolt and blunt force trauma.337 cluding level of distress and times to unconsciousnessWhether pain is perceived is not known. Consciousness or death, are not available. Based on current knowledgeand perception of pain are not necessarily concurrent. of avian physiology and euthanasia, thoracic compres- sion can result in significant levels of pain and distress Decapitation—Based on information currently before animals become unconscious, thus lacking keyavailable, decapitation is considered to be acceptable humane considerations that can be addressed by otherwith conditions for euthanasia of small (< 200 g) birds. methods. Various veterinary and allied groups do notThe AAZV Guidelines for Euthanasia of Nondomestic support thoracic compression as a method of euthana-Animals416 also lists decapitation as acceptable with sia.413–416 Consequently, thoracic compression is gener-conditions, and suggests the method may be preferred ally an unacceptable means of euthanizing animals thatover cervical dislocation under certain field conditions are not deeply anesthetized or insentient due to otherdue to clear evidence of a successful procedure. One reasons, but is appropriate as a secondary method forstudy54 indicated that several methods of partial, me- animals that are insentient. Details are available in thechanical decapitation of chickens (weighing 2.1 to 3.5 Physical Methods section of the Guidelines.kg [4.6 to 7.7 lb]) did not result in the loss of visuallyevoked responses in 90% of cases when compared with S5.3 EGGS, EMBRYOS, AND NEONATESuse of a percussion bolt pistol and concluded that fewer Bird embryos that have attained > 50% incubationthan 10% of cervical dislocations resulted in concus- have developed a neural tube sufficient for pain per-sion. In another study decapitation applied to anesthe- ception; therefore they should be euthanized by simi-tized chickens resulted in visually evoked responses lar methods used in avian neonates such as anestheticup to 30 seconds following decapitation, but because overdose, decapitation, or prolonged (> 20 minutes)the responses were obtained from anesthetized chick- exposure to CO2.52,132,416 Eggs at < 50% incubation mayens it is not possible to conclude any association with be destroyed by prolonged exposure (> 20 minutes) tocognitive processes.52–54 As indicated previously (see CO2,334 cooling (< 4°C for 4 hours), or freezing.52,416 An-discussion of Consciousness and Unconsciousness in esthesia can be used prior to euthanasia and is mostthe Guidelines), at some level between behavioral un- easily accomplished with exposure to inhaled anesthet-responsiveness and the induction of a flat EEG, con- ics via entry into the air cell at the large end of the egg.sciousness must vanish; however, EEG data cannot pro- Egg addling can also be used to destroy the viability ofvide definitive answers as to onset of unconsciousness. embryos.416 Gunshot—Gunshot is not recommended as a meth- S6. FINFISH AND AQUATIC INVERTEBRATESod for captive birds, where restraint is feasible. Its usefor wild birds is addressed in the Captive and Free- S6.1 GENERAL CONSIDERATIONSRanging Nondomestic Animals section of the Guide- Finfish and aquatic invertebrates play importantlines. roles as food, pets, research subjects, display animals, sources of recreation, and key components of healthyS5.2.3 Adjunctive Methods ecosystems. In each of these situations it may be neces- Potassium chloride—Although administration of sary to cause the death of some animals. Considerablepotassium chloride to a conscious, unanesthetized bird evidence is accumulating suggesting it is appropriate tois considered to be an unacceptable method of euthana- consider the possibility of pain perception in these spe-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 67
  • 68. cies.66,71–73,539–547 The aim is to accomplish death for these invertebrates, optimal methods for euthanasia will vary.animals rapidly with the minimum amount of pain and Euthanasia choices for finfish and aquatic invertebratesdistress practicable. Because the environment associated must account for animal stress responses and humanwith finfish and aquatic invertebrates in each of their safety concerns associated with handling, as well as dif-roles is different, and because knowledge about the evo- ferences in metabolism, respiration, and tolerance to ce-lutionary and societal status of poikilothermic animals rebral hypoxia. Virtually all methods require that person-(lower vertebrates and invertebrates) is limited, identify- nel be carefully trained and monitored (although someing and applying appropriate criteria for euthanasia can carry more risks of human ineffectiveness than others),be difficult. some require DEA registration and record keeping, ex- tralabel use requires administration by or under the su-S6.1.1 Terms Applicable to Ending Life pervision of a veterinarian, and chemicals regulated by Specific to finfish, the three main terms used to de- the EPA can only be legally used according to their labelscribe the ending of life are euthanasia, slaughter, and directions. Intracoelomic injections carry an inherenthumane killing (Table 2). There is often confusion re- risk of organ damage and response time may vary. Intra-garding how these terms and their associated methods venous injections require careful handling of finfish, asdiffer. The methods described in the Guidelines serve as well as trained and experienced personnel. Intramuscu-guidance for veterinarians and others who may need to lar injections with ketamine, α2 adrenergic receptor ago-perform euthanasia. The Guidelines are not intended to nists, or Telazolh can be administered via pole syringe orspecifically address slaughter or humane killing methods. dart gun to larger finfish to facilitate handling and reduceSlaughter is used primarily to describe the humane killing handling stress for finfish, but rarely achieve surgicalof animals intended for human consumption for food or planes of anesthesia in teleosts. In all cases, veterinariansother uses (eg, agricultural harvest, commercial fishing). and others with expertise relevant to the species of inter-Humane killing is less specific and can be used to describe est should be consulted; professional judgment and rel-some recreational fishing practices and may also include evant expertise should be taken into account when ulti-activities such as finfish sampling, depopulation, eradica- mately determining the best method to use. In addition,tion, and control to eliminate unwanted finfish (including it is often more difficult to ascertain when a finfish or andiseased or nonnative finfish) from a water body. A fourth aquatic invertebrate is dead as compared with birds andterm, harvest, specifically refers to the act or process of mammals. Some unique aspects of euthanasia for finfishgathering a crop, as in aquaculture and commercial fish- have been described.552,553ing; however, harvest may also be used to describe finfishremoved from a water body by anglers. Whether harvested S6.1.3 Preparation and Environmentfinfish are slaughtered or humanely killed depends on the As a general principle the preparations for euthana-context of the activity.548–551 Neither slaughter nor humane sia of finfish should be very similar to the preparationskilling is addressed by this document. Addressing eutha- for anesthesia of finfish.554–556 If possible, withholdingnasia of invertebrates in some settings is not meant to food for 12 to 24 hours prior to euthanasia will reducediscount the necessity for and suitability of slaughter and regurgitation, defecation, and nitrogenous waste pro-pest control techniques that do not meet the definition of duction. The environment should be as quiet and non-euthanasia. Nor is the intent of this document to advocate stimulatory as possible given the circumstances. Lightthe expansion of coverage of IACUC to invertebrates. intensity should be reduced if possible, but with ade- quate lighting for personnel. This can also be achievedS6.1.2 Human and Animal Considerations through use of a dark or opaque container and lid, or by Because of the diversity of physiologic and anatomic use of less intense lighting, (eg, red light illumination,characteristics seen among species of finfish and aquatic as red light does not penetrate water well).Table 2—Terms used to describe the deliberate ending of the lives of finfish. (Adapted with permission from Yanong RPE, Hartman KH,Watson CA, et al. Fish slaughter, killing, and euthanasia: a review of major published US guidance documents and general consider-ations of methods. Publication #CIR1525. Gainesville, Fla: Fisheries and Aquatic Sciences Department, Florida Cooperative ExtensionService, Institute of Food and Agricultural Sciences, University of Florida, 2007 Available at: edis.ifas.ufl.edu/fa150. Accessed May 16, .2011.) Term Possible applications Examples Slaughter •Agricultural harvest •Catfish, salmon, and tilapia •Commercial fisheries •Wild-caught grouper and snapper Humane killing •Recreational fisheries •Largemouth bass and red drum •Depopulation or eradication •Nonnative species eradication (eg, walking catfish) •Control •Population disease control or testing (eg, outbreaks of spring viremia of carp [SVC*] or viral hemorrhagic septicemia [VHS*]) •Sampling •Large-scale ecological research, open ocean collection Euthanasia •Pets •Hobbyist koi and goldfish, tropical finfish •Zoo animals •Public aquarium shark •Laboratory research •Small-scale toxicology work in zebra danios •Some field research •Some small-scale ecological research *Spring viremia of carp (SVC) and viral hemorrhagic septicemia (VHS) are viral diseases that are under international and national regulatory control and for which depopulation of infected populations is warranted.68 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 69. Water quality should be similar to that of the en- S6.1.6 Finfish and Aquatic Invertebratesvironment from which the finfish originated, or opti- Intended for Human Consumptionmized for that species and situation, for the duration As previously indicated, the term slaughter is usedof euthanasia. If of acceptable quality for finfish health, primarily to refer to the killing of animals intended forwater in which they have been house or captured human consumption (eg, agricultural harvest, com-should be used, and supplemental aeration and temper- mercial fisheries) and these Guidelines are not intendedature control may be necessary. Either the immersion to address that activity. However, when euthanasia ofeuthanasia solution is prepared with water from the animals intended for human consumption is desired,finfish housing system and the finfish are transferred tissue residues from the use of drugs and other chemi-into it or a concentrated form of the anesthetic agent cals will make many methods unacceptable unless theyas a solution (containing buffering agent if appropri- have been approved by the FDA for this purpose andate) is introduced directly into the container of finfish appropriate withdrawal periods are followed. Use ofto minimize stressors. If euthanizing a large population any unapproved chemicals for euthanasia prohibits en-of finfish, it is important to monitor the anesthetic bath try of the finfish into the food chain, either by render-water quality (temperature, dissolved O2, and organic ing, as fish meal, or as directly consumed product.549loading, in particular). The euthanasia agent may need With that said, currently there are no drugs approvedto be supplemented or replaced periodically. Euthana- for euthanasia of finfish or aquatic invertebrates. Car-sia methods should be tested in one animal or a small bon dioxide is a drug of low regulatory priority317 thatgroup of animals prior to use in a large population for avoids unacceptable residues, but it is not an FDA-an unfamiliar species.325 If handling is required, appro- approved method for killing aquatic animals used forpriate equipment (nets, gloves) should be used to mini- food. Physical methods that are acceptable with condi-mize stressors. tions include manually applied blunt force trauma to the head, decapitation, and pithing.S6.1.4 Indicators of Death in Finfishand Aquatic Invertebrates S6.2 FINFISH Because the thousands of species of finfish and Common methods used to euthanize finfish in-aquatic invertebrates vary greatly in anatomic and clude noninhaled methods (ie, immersion and injec-physiologic characteristics, reliable indicators of death tion) and physical methods. Because of general differ-may not be available for some. However, there are some ences in anatomy and application seen between finfishstandard approaches that can be useful for many of the and terrestrial animals (especially with regard to prima-more commonly encountered species. Loss of move- ry respiratory organs, and aqueous vs air environment),ment, loss of reactivity to any stimulus, and initial flac- techniques involving addition of drugs to the finfish’scidity (prior to rigor mortis) may serve as indicators of environment (ie, the water), for purposes of this docu-death for finfish and some aquatic invertebrates. More ment, are considered noninhaled methods.useful indicators for many finfish include respiratory Descriptions of methods used to euthanize finfisharrest (cessation of rhythmic opercular activity) for a follow and include 1-step and 2-step procedures. Eachminimum of 10 minutes and loss of eyeroll (vestibulo- method is further classified as acceptable, acceptableocular reflex, the movement of the eye when the finfish with conditions, or unacceptable considering charac-is rocked from side to side). The latter is no longer pres- teristics of the methods and the environments in whichent in finfish that have been deeply anesthetized or eu- euthanasia is conducted, including veterinary privatethanized.557 The heart can continue to contract even af- practice (eg, companion and ornamental [display] fin-ter brain death or removal from the bodies of finfish,558 fish), ornamental (aquarium) finfish wholesale and retailso the presence of a heartbeat is not a reliable indicator facilities, research laboratories, and finfish kept outdoorsof life, but sustained absence of heartbeat is a strong and in fisheries. An acceptable method reliably meets theindicator of death. For more sessile, less active organ- requirements of euthanasia. Methods that are acceptableisms, or those with specific anatomic or physiologic ad- with conditions reliably meet the requirements of eutha-aptations that prevent use of these indicators, it may be nasia when specified conditions are met. An unaccept-more difficult to assess loss of consciousness and death, able method does not meet the requirements of euthana-and consultation with species experts is recommended. sia. Because finfishes’ anatomic and physiologic charac- teristics are quite different from those of mammals andS6.1.5 Disposition of Euthanized Animals birds, classification of techniques may vary from what Any euthanized finfish or invertebrate should be has been recommended for other species.promptly removed from its aquarium, pond, or othervessel and disposed of according to all pertinent fed- S6.2.1 Noninhaled Agentseral, state, and local regulations, in a manner that will Immersion (1 step)—Intentional overdose via im-reduce the risk of disease spread, prevent pests and mersion in anesthetic solutions is a common methodother nontarget species from gaining access to animal of euthanasia for finfish.325,559–561 Finfish should be leftremains, and ensure human and environmental safety. in the anesthetic solution for a minimum of 10 minutesPreventing environmental contamination by any life after cessation of opercular movement.63,325,559 Optionsstage of finfish that could hatch and/or survive outside include the following:an acceptable, enclosed body of water is an important (1) Benzocaine or benzocaine hydrochloride, buff-consideration in confirmation of death and disposal of ered. Solutions for immersion should be prepared inthe animal’s remains. concentrations Ն 250 mg/L and should be buffered.561AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 69
  • 70. (2) Carbon dioxide. Immersion in CO2-saturated required for euthanasia may vary depending upon thewater causes narcosis and loss of consciousness after species, life stage, and water chemistry parameters. Aseveral minutes.63,325 Some species may exhibit hyper- concentration of 250 to 500 mg/L, or 5 to 10 times theactivity prior to loss of consciousness.559 Purity and anesthetic dosage, is effective for most species.325,561 MSconcentration of CO2 are important for effectiveness. 222 at a dose of 400 mg/L has been shown to be ineffec-Only CO2 from a source that allows for careful regula- tive for a few species (eg, Gulf of Mexico sturgeon).325tion of concentration, such as from cylinders, is accept- Finfish that are too large for practical or cost-effectiveable. Care must be taken when using CO2 to prevent ex- immersion in lethal doses of buffered MS 222 can beposure to personnel (ie, euthanasia must be conducted euthanized by applying the concentrated, buffered so-in well-ventilated areas). lution directly to the gills.325,559 (3) Ethanol. Ethanol has been suggested as an ac- (8) 2-phenoxyethanol. Solutions for immersionceptable alternative method for finfish.306 The depres- should be prepared in concentrations Ն 0.5 to 0.6 mL/Lsive effects of ethanol on the CNS are well described,562 or 0.3 to 0.4 mg/L.309and exposure of zebrafish via immersion has becomea model for behavioral and molecular responses to Injection—Injectable agents have been adminis-alcohol, at concentrations from 10 to 30 mL of 95% tered for euthanasia via IV, intracoelomic, IM, and in-ethanol/L.563–565 At this dose, alcohol induces anesthe- tracardiac routes.306,325sia, and prolonged immersion produces death via respi- (1) Pentobarbital (1 step). Sodium pentobarbitalratory depression causing anoxia. This is not equivalent (60 to 100 mg/kg [27.3 to 45.5 mg/lb]) can be admin-to immersing finfish directly into preservative concen- istered by IV, intracardiac, or intracoelomic routes fortrations of ethanol (70%), which is not acceptable as a euthanasia.63 Pentobarbital may also be administeredeuthanasia method. via intracardiac injection for anesthetized animals as (4) Eugenol, isoeugenol, and clove oil. Whenever the second step of a 2-step euthanasia procedure. Deathpossible, products with standardized, known concen- usually occurs within 30 minutes.trations of essential oils should be used so that accurate (2) Ketamine (2 step). Ketamine may be admin-dosing is possible. Concentrations required for anes- istered at dosages from 66 to 88 mg/kg568 (30 to 40thesia will vary depending on species and other factors, mg/lb) via an IM injection followed by a lethal dose ofbut may be as low as 17 mg/L for some species. Greater pentobarbital. Observers should be advised about theconcentrations will be required for euthanasia.566–568 possibility of ketamine-induced muscle spasms duringFinish should be left in the anesthetic solution for a induction.325minimum of 10 minutes after cessation of opercular (3) Ketamine:medetomidine (2 step). A combina-movement. These compounds are equivocal or known tion of ketamine, at dosages of 1 to 2 mg/kg, with me-carcinogens according to the National Toxicology Pro- detomidine, at dosages of 0.05 to 0.1 mg/kg (0.02 togram.318 Some studies in rodents indicate this group 0.05 mg/lb), may be administered via IM injection fol-of anesthetics may cause paralysis in addition to hav- lowed by a lethal dose of pentobarbital.568ing anesthetic effects, and analgesic properties are un- (4) Propofol (2 step). A dose of 1.5 to 2.5 mg/kgknown.321–324 Because some clove oil products may con- (0.7 to 1.1 mg/lb) can be administered IV followed bytain or include either methyleugenol or isoeugenol, or an injection of a lethal dose of pentobarbital.568both, FDA has expressed concern that the use of cloveoil or its components in finfish may adversely affect hu- S6.2.2 Physical Methodsman food safety and animal food safety. In addition, be- The following methods can be applied for euthana-cause clove oil and its components have not been eval- sia, providing they are performed using proper equip-uated for target animal safety, FDA is also concerned ment by trained personnel who are regularly monitoredthat the use of any of these compounds may adversely for proficiency.affect finish, including endangered aquatic species.569 (1) Decapitation followed by pithing (2 step). Rap-Isoeugenol is a potential carcinogen318 so human safety id severance of the head and brain from the spinal cord,in the application of that agent is of concern. followed by pithing of the brain, will cause rapid death (5) Isoflurane, sevoflurane. These concentrated liq- and unconsciousness. Decapitation alone is not con-uid anesthetics can be added to water, although they are sidered a humane approach to euthanasia, especiallygenerally not very water soluble.559 Injecting the solu- for species that may be particularly tolerant of low O2tion through a syringe and fine gauge needle under the concentrations. Pithing helps ensure rapid loss of brainwater in the container used for euthanizing is helpful in function and death for those species.570ensuring dispersal in the water. Doses of > 5 to 20 mL/L (2) Cervical transection using a knife or othercan be used (10 times the upper range for anesthesia). sharp instrument inserted caudal to the skull to severHowever, because both anesthetics are highly volatile, the spinal cord and cervical vertebrae, followed by pith-human safety is of concern and use in a well-ventilated ing (2 step). The rationale for this approach is similararea is imperative. to that for decapitation (destruction of connections be- (6) Quinaldine sulfate. Solutions for immersion tween brain and spinal cord) and pithing (destructionshould be prepared in concentrations Ն 100 mg/L.309 of brain tissue), except that the head is still physicallyQuinaldine sulfate will acidify water; therefore, buffer- attached by musculature to the body.ing is required to prevent distress from acute drop in pH. (3) Manually applied blunt force trauma (cranial (7) Tricaine methanesulfonate, buffered (MS 222, concussion) followed by pithing (2 step). ManuallyTMS). Solutions must be buffered, and concentrations applied blunt force trauma (a rapid, accurately placed70 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 71. blow of sufficient energy to the cranium with an appro- temperature must not exceed 2° to 4°C. Well-insulatedpriate-sized club) can cause immediate unconscious- containers, such as coolers, will assist in maintainingness and potentially death, but should be followed by the ice slurry and a probe thermometer can be used topithing to ensure death. The finfish’s size, species, and confirm water temperature.anatomy and characteristics of the blow (including its This method of euthanasia is not appropriate foraccuracy, speed, and club mass) will determine the ef- temperate, cool, or cold-water–tolerant finfish, such asficacy of manually applied blunt force trauma. This pro- carp, koi, goldfish, or other species that can survive atcedure requires training and monitoring for proficiency. 4°C and below. It is appropriate for zebrafish and otherAnatomic features, such as the location of the eyes, can small-bodied (3.8-cm-long or smaller) tropical and sub-help serve as a guide to the location of the brain.570,571 tropical stenothermic finfish, for which the lower lethal (4) Captive bolt (most commonly nonpenetrating; temperature range is above 4°C.316,461,462 This method1 step). This is a method usually applied to large finfish can also be acceptable for small to medium-sized (2.8-species.570 to 13.5-cm-long) Australian river gizzard shad, as long (5) Maceration (1 step). When applied correctly, as secondary euthanasia methods are applied after fin-using a well-maintained macerator specifically de- fish are rendered nonresponsive.316 However, because ofsigned for the size of finfish being euthanized, death surface-to-volume considerations, use of this method isis nearly instantaneous.572 The process is aesthetically not appropriate in other medium to large-bodied finfishunpleasant for some operators and observers. until data regarding its applicability to euthanasia for (6) Rapid chilling (hypothermic shock; 1 step or 2 those species become available.step). It is acceptable for zebrafish (D rerio) to be eutha-nized by rapid chilling (2° to 4°C) until loss of orienta- S6.2.3 Adjunctive Methodstion and operculum movements316,461,462 and subsequent Decapitation, pithing, freezing, and other physicalholding times in ice-chilled water, specific to finfish methods for inducing death may be used as the sec-size and age. Zebrafish adults (approx 3.8 cm long) can ond step of a 2-step procedure when finfish have beenbe rapidly killed (10 to 20 seconds) by immersion in 2° rendered unconscious prior to their application by anto 4°C (36° to 39°F) water. Adult zebrafish should be acceptable or acceptable-with-conditions, first-stepexposed for a minimum of 10 minutes and fry 4 to 7 method. If necessary to ensure death, rapid chilling fordpf for at least 20 minutes following loss of operculum specified groups may be followed by either an approvedmovement. Use of rapid chilling and use of buffered MS adjunctive euthanasia method or a humane killing222 alone have been shown to be unreliable euthana- method. Use of a dilute sodium hypochlorite or calci-sia methods for zebrafish embryos < 3 dpf. To ensure um hypochlorite solution may be an adjunctive methodembryonic lethality these methods should be followed for early life stages of finfish, including embryos andwith an adjunctive method such as use of diluate sodi- larvae.327,462um or calcium hypochlorite solution at 500 mg/L.327,462If necessary to ensure death of other life stages, rapid S6.2.4 Unacceptable Methodschilling may be followed by either an approved adjunc- The following are unacceptable methods of eutha-tive euthanasia method or a humane killing method. nasia in any situation. Flushing of finfish into sewer, sep-Until further research is conducted, rapid chilling is ac- tic, or other types of outflow systems is unacceptable forceptable with conditions for other small-bodied, simi- many reasons. Water chemistry and quality may delaylarly sized tropical and subtropical stenothermic spe- time to death and result in exposure to noxious com-cies. Species-specific thermal tolerance and body size pounds. For systems in close proximity to and/or con-will determine the appropriateness and effectiveness nected to natural waterways, pathogen release or trans-of rapid chilling for euthanasia of finfish. Finfish size mission may occur from diseased or carrier animals.is important because the rate of heat loss via thermal Slow chilling or freezing of unanesthetized animals, in-conduction from a body is proportional to its surface cluding placing finfish into a freezer without prior anes-area. Based on these 2 factors, it has been suggested that thesia, is also an unacceptable method. Similarly deathrapid chilling in water associated with an ice slurry is a by anoxia and dessication after removal from the watersuitable killing method for small tropical and subtropi- or by anoxia in water; any death due to exposure to caus-cal finfish species 3.8 cm in length (tip of the snout to tic chemicals; and death including prolonged traumaticthe posterior end of the last vertebra) or smaller, having injury prior to unconsciousness are unacceptable.lower lethal temperatures above 4°C. While metomidate has been used for euthanasia of To ensure optimal hypothermal shock (ie, rapid some finfish species, its listing in the Index of Legallykilling), transfer of finfish into ice water must be com- Marketed Unapproved New Animal Drugs for Minorpleted as quickly as possible. This means rapid tran- Species by the FDA (with a specified use for sedationsitions from acclimatization temperature to 2° to 4°C and anesthesia) means that its extralabel use for eutha-must be achieved. This can be accomplished by using nasia is currently illegal.minimal water volume to transfer finfish (ie, using anet to place finfish in chilled water). In addition, fin- S6.2.5 Life Stage Considerationsfish should not be in direct contact with the ice in the The effectiveness of euthanasia methods describedwater; rather a depression should be formed in the ice in these guidelines may vary by life stage, as well asslurry to expose the entire surface of the finfish to the by species. Early stages in the lives of finfish, includingchilled water. Full contact with cold water ensures op- embryos and larvae, may require higher concentrationstimal exposure and rapid chilling of the finfish. Water of immersion anesthetics or a longer duration of ex-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 71
  • 72. posure.560 As an example, immersion in a buffered MS posure.560 As an example, immersion in a buffered MS222 solution having a concentration > 1 g/L is not a 222 solution having a concentration > 1 g/L is not areliable method for killing some finfish in younger life reliable method for killing some finfish in early lifestages.461,462,560 For some species and in some situations, stages.461,462,560 For some species and in some situa-adjunctive methods to guarantee death may need to be tions, adjunctive methods to guarantee death mayapplied for these animals after anesthesia with buffered need to be applied for these animals after anesthesiaMS 222. Rapid chilling followed by an adjunctive meth- with buffered MS 222.od such as immersion in a dilute sodium hypochlorite Rapid chilling followed by immersion in a diluteor calcium hypochlorite solution is acceptable for ze- sodium hypochlorite or calcium hypochlorite solu-brafish embryos and larvae as a 2-step method and is tion is acceptable for zebrafish embryos and larvae as aalso acceptable with conditions as a 2-step method for 2-step method and is also acceptable with conditions asdestruction of other (nonzebrafish) species’ embryos a 2-step method for destruction of other (nonzebrafish)and larvae.327,462 species’embryos and larvae.327,462S6.2.6 Finfish in Particular Environments S6.2.6.2 Aquarium Finfish Wholesale and Retail FacilitiesS6.2.6.1 Veterinary Private Practice— Freshwater and marine aquarium finfish are com-Companion and Ornamental (Display) Finfish mercially collected from the wild, and are also bred in Clients with pet or display finfish of any species captivity. Tropical aquarium finfish are sold at retail petoften value them as companion animals and share a shops and finfish stores from systems housing one orhuman-animal bond similar to that seen between cli- more species of finfish per tank. Individual finfish orents and other pets, such as dogs and cats. Therefore, populations of finfish may become injured or diseasedit is important to consider the perception of the client and require euthanasia. Methods of euthanasia used inwhen euthanasia methods are chosen. Clients should this environment need to be applicable to individualbe offered the opportunity to be present during eutha- finfish, to all finfish in an aquarium, to finfish held innasia whenever feasible; however, clients also should be multiple aquariums on a central filtration system, or foreducated as to what method will be used and what they finfish kept in ponds. In certain situations euthanasiamay observe during euthanasia. For example, clients may not be feasible and depopulation methods may bemay believe the excitement phase of anesthesia, which required.can result in increased motor activity or the appearance The following methods are acceptable for use inof agitation,559 is unduly painful or stressful for the fin- this environment:fish even when it is not. Immersion in solutions of buffered tricaine meth- The following methods are acceptable for use in anesulfonate (MS 222), buffered benzocaine, and quin-this environment: aldine sulfate. Finfish should be left in the anesthetic (1) Immersion in solutions of buffered tricaine solution for a minimum of 10 minutes after cessationmethanesulfonate (MS 222), buffered benzocaine, of opercular movement.63,325,559isoflurane and sevoflurane, quinaldine sulfate, and The following methods are acceptable with condi-2-phenoxyethanol. tions for use in this environment: (2) Injections of pentobarbital, ketamine followed (1) Immersion in CO2-saturated water; eugenol,by pentobarbital, a combination of ketamine and me- isoeugenol, or clove oil; and ethanol.detomidine followed by pentobarbital, and propofol (2) Decapitation, cervical transection, or manuallyfollowed by pentobarbital. Owners should be advised applied blunt force trauma as step 1 of a 2-step method,about the possibility of ketamine-induced muscle followed by pithing.spasms during induction when using that agent. (3) Freezing may be used as an adjunctive method The following methods are acceptable with condi- following anesthesia.tions for use in this environment: (4) Rapid chilling (hypothermic shock) for small- (1) Immersion in eugenol, isoeugenol, or clove bodied (3.8-cm-long or smaller) tropical and subtropi-oil. Finfish should be left in the solution for a mini- cal stenothermic finfish, for which the lower lethal tem-mum of 10 minutes after cessation of opercular move- perature range is above 4°C.316,461,462ment.63,325,559 The following methods are not recommended for The following methods are not recommended for use in this environment:use in this environment: Use of injectable anesthetic drugs including bar- (1) Immersion in CO2-saturated water is not rec- biturates, requires the oversight of a veterinarian andommended because some finfish exposed to this meth- DEA permitting for controlled substances. Therefore,od may become hyperactive, which can be disconcert- unless a veterinarian is available on-site to oversee useing for staff and owners. of these drugs, this method is not recommended in this (2) Manually applied blunt force trauma to the environment.head, decapitation, and pithing are not recommended Early stages in the lives of finfish, including embryosbecause their application can be distressing for owners and larvae, may require higher concentrations of immer-and staff. sion anesthetics or a longer duration of exposure.560 As Early stages in the lives of finfish, including em- an example, immersion in a buffered MS 222 solutionbryos and larvae, may require higher concentrations having a concentration > 1 g/L is not a reliable methodof immersion anesthetics or a longer duration of ex- for killing some finfish in early life stages.461,462,560 For72 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 73. some species and in some situations, adjunctive meth- concussion) followed by pithing.ods to guarantee death may need to be applied for these Early stages in the lives of finfish, including embryosanimals after anesthesia with buffered MS 222. and larvae, may require higher concentrations of immer- Rapid chilling followed by immersion in a dilute sion anesthetics or a longer duration of exposure.560 Assodium hypochlorite or calcium hypochlorite solu- an example, immersion in a buffered MS 222 solutiontion is acceptable for zebrafish embryos and larvae as a having a concentration > 1 g/L is not a reliable method2-step method and is also acceptable with conditions as for killing some finfish in earlier life stages.461,462,560 Fora 2-step method for destruction of other (nonzebrafish) some species and in some situations, adjunctive methodsspecies’embryos and larvae.327,462 to guarantee death may need to be applied for these ani- mals after anesthesia with buffered MS 222.S6.2.6.3 Research Facilities Rapid chilling followed by immersion in a dilute Researchers working in laboratories should have sodium hypochlorite or calcium hypochlorite solu-materials readily available to provide appropriate eu- tion is acceptable for zebrafish embryos and larvae as athanasia for their research subjects when required, and 2-step method and is also acceptable with conditions asshould be trained and monitored for proficiency in the a 2-step method for destruction of other (nonzebrafish)use of chosen techniques. Many facilities using finfish species’embryos and larvae.as research subjects are engaged in biomedical research.Zebrafish are the most common species used for re- S6.2.6.4 Finfish Kept Outdoors and in Fisheriessearch and are usually kept in small-scale tank systems; Field research on finfish takes place in a complexhowever, some research facilities may also have large- environment that must be understood by both research-scale housing and production systems and/or keep ers and their respective IACUC.320 Field research is fre-other larger species of finfish, and consequently, need quently conducted on a scale comparable to commercialto consider additional options for euthanasia.320 The fishing, often with the same equipment, boats, and per-expertise of those knowledgeable about these settings sonnel. The large number of finfish, limited boat space,and species should be sought as necessary. adverse environmental conditions, and personnel safety The following methods are acceptable for use in concerns may justify use of harvest techniques that maythis environment: not meet the criteria for euthanasia, but in all situations, (1) Immersion in solutions of buffered tricaine pain and distress should be minimized to the greatest ex-methanesulfonate (MS 222), buffered benzocaine, tent possible. Similarly, fisheries biologists may be facedquinaldine sulfate, and 2-phenoxyethanol. Finfish eu- with situations involving numerous finfish requiring de-thanized with these methods must not enter the food population (eg, invasive species) rather than euthanasia.supply. Fieldwork on finfish may also be conducted on a (2) Rapid chilling (hypothermic shock) is accept- smaller scale under conditions that make euthanasiaable for zebrafish (D rerio) and Australian river gizzard feasible. In such cases, the following methods shouldshad (N erebi) as long as transfer from acclimatized be applied and convenience for the researcher shouldtemperatures to water associated with a 2° to 4°C ice not be a primary consideration.slurry occurs rapidly with as little transfer of warmer The following methods are acceptable for use inwater as possible. this environment: The following methods are acceptable with condi- (1) Immersion in solutions of buffered tricainetions for use in this environment: methanesulfonate (MS 222), buffered benzocaine, (1) Immersion in CO2-saturated water (as long as quinaldine sulfate, isoflurane or sevoflurane, quinal-observers are advised and can accept that some finfish dine sulfate, and 2-phenoxyethanol. Although a gen-exposed to this method may exhibit hyperactivity and eral concern for all environments and situations, theappears to be in distress), eugenol, isoeugenol, or clove potential effects of drug residues and proper disposal ofoil. animal remains should be considered when using any (2) Rapid chilling (hypothermic shock) to 2° to 4°C of these drugs.is acceptable with conditions for small-bodied (3.8-cm- (2) An injection of pentobarbital (60 to 100 mg/kg)long or smaller) tropical and subtropical stenothermic can be administered IV or intracoelomically.309 Pento-finfish, for which the lower lethal temperature range barbital may also be administered intracardially in anes-is above 4°C. Because of surface-to-volume consider- thetized animals. Two-step injection procedures mayations, use of this method is not appropriate for other also be used, including ketamine (IM) followed by amedium to large-bodied finfish until additional data for lethal dose of pentobarbital; a combination of ketaminethose species become available. and medetomidine (IM) followed by a lethal dose of (3) Maceration is acceptable with conditions when pentobarbital; and propofol (IV) followed by a lethaldeath is instantaneous using a well-maintained mac- dose of pentobarbital. Although a general concern forerator designed for the size of finfish being euthanized. all environments and situations, the potential effects ofThe process is likely to be aesthetically unpleasant for drug residues and proper disposal of animal remainsthose observing it. should be considered when using any of these drugs. (4) Decapitation followed by pithing. Rapid sever- The following methods are acceptable with condi-ance of the head and brain from the spinal cord, fol- tions for use in this environment:lowed by pithing of the brain, will cause rapid death (1) Immersion in CO2-saturated water or eugenol,and unconsciousness.320 isoeugenol, or clove oil. (5) Manually applied blunt force trauma (cranial (2) Manually applied blunt force trauma to theAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 73
  • 74. head followed by pithing. nasia of crustaceans (0.125 mL/L).133,573 Isoeugenol is a (3) Decapitation followed by pithing. Decapitation potential carcinogen318 so human safety in the applica-alone is not considered a humane form of euthanasia, tion of that agent is of concern.especially for species that may be particularly tolerantof low O2 concentrations. Pithing helps ensure rapid Ethanol—Ethanol has been used for euthanasiadeath for those species. of some phyla (at a 1% to 5% concentration as com- (4) Cervical transection followed by pithing. The pared with concentrations of > 70% used for preser-rationale for this approach is similar to that for decapi- vation), and acts by inhibiting neuronal sodium andtation and pithing, except that the head is still physi- calcium channels in molluscs.562 Initial aversion and/cally attached by musculature to the body. or excitement has been reported as occurring in cepha- (5) Captive bolt. This method is usually applied to lopods.134,574large finfish species. Other agents for euthanasia, while less common, (6) Rapid chilling (hypothermic shock) in water have been described and may be useful for specific ap-of 2° to 4°C for small-bodied (3.8-cm-long or smaller) plications.133tropical and subtropical stenothermic species (as pre-viously described for zebrafish). Because of surface-to- S6.3.2 Acceptable Secondvolume considerations, use of this method is not appro- Steps of 2-Step Methodspriate in medium to large-bodied finfish until pertinentdata for those species becomes available. S6.3.2.1 Noninhaled Agents for Immersion Early stages in the lives of finfish, including em- Noninhaled agents that can be administered viabryos and larvae, may require higher concentrations immersion as the second step of a 2-step euthanasia ap-of immersion anesthetics or a longer duration of ex- proach include 70% alcohol and neutral-buffered 10%posure.560 As an example, immersion in a buffered MS formalin. These agents are not acceptable, however, for222 solution having a concentration > 1 g/L is not a immersion as a single-step procedure, nor as the firstreliable method for killing some finfish in early life step of a 2-step procedure.stages.461,462,560 For some species and in some situations,adjunctive methods to guarantee death may need to be S6.3.2.2 Physical Methodsapplied for these animals after anesthesia with buffered Pithing, freezing, and boiling are acceptable asMS 222. Rapid chilling followed by immersion in a di- the second step (adjunctive methods) of a 2-step eu-lute sodium hypochlorite or calcium hypochlorite solu- thanasia procedure. Pithing requires detailed anatomiction is acceptable for zebrafish embryos and larvae as a knowledge of the species in question. These methods2-step method and is also acceptable with conditions as are not acceptable, however, as a single-step procedure,a 2-step method for destruction of other (nonzebrafish) nor as the first step of a 2-step procedure.species’ embryos and larvae.327,462 S6.3.3 Life Stage ConsiderationsS6.3 AQUATIC INVERTEBRATES The effectiveness of euthanasia methods described Overdose of a general anesthetic is as appropriate a in the Guidelines may vary depending on life stageeuthanasia strategy for aquatic invertebrates as it is for and species. As for finfish, this should be consideredfinfish. And, immersion is an effective route of adminis- when euthanizing aquatic invertebrates. Methods usedtration of anesthetic and euthanasia agents.133,330 for different life stages of the same species may require Because confirming the death of many invertebrates modification to maximize their effectiveness. Recom-is difficult, 2-step euthanasia procedures are often rec- mendations regarding use of adjunctive methods (asommended in which chemical induction of anesthesia, described previously) may also be necessary to guar-nonresponsiveness, or presumptive death is followed antee death.by an adjunctive method that destroys the brain or ma-jor ganglia physically (eg, pithing, freezing, boiling) or S6.3.4 Unacceptable Methodschemically (eg, alcohol, formalin). Application of the Methods of killing that do not cause rapid death orlatter methods by themselves is generally not consid- that cause trauma prior to loss of consciousness are notered to meet the criteria established for euthanasia.133,330 considered humane methods of death, or euthanasia. These can include removing a finfish or aquaticS6.3.1 Acceptable First Steps of 2-Step Methods invertebrate from the water and allowing it to die by hypoxia secondary to desiccation of gill tissue; leavingS6.3.1.1 Noninhaled Agents for Immersion finfish or aquatic invertebrates in a container of water Magnesium salts—Magnesium salts are a near-uni- without adequate aeration, causing death by anoxia; orversal anesthetic agent, relaxing agent, and euthanasia any death due to exposure to caustic chemicals or trau-agent for aquatic invertebrates, although they are inef- matic injury without first inducing unconsciousness infective for crustaceans. A range of concentrations has the finfish or aquatic invertebrate.been recommended for various phyla. Research sug-gests the magnesium ion acts centrally in suppressing S7. CAPTIVE AND FREE-RANGINGneural activity of cephalopods.134 NONDOMESTIC ANIMALS Methods acceptable with conditions are equivalent Clove oil or eugenol—Clove oil or eugenol has been to acceptable methods when all criteria for applicationused effectively as an immersion agent for the eutha- of a method are met.74 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 75. in the period leading up to euthanasia will allow theS7.1 GENERAL CONSIDERATIONS animal to be as comfortable as possible. Most small ani- The nondomestic captive and free-ranging animals mals will find security in a dimly lighted, appropriatelydiscussed in the following sections vary substantially bedded and ventilated crate, box, tube, or similar con-in their anatomic and physiologic characteristics, na- tainer as this simulates a natural tendency to hide fromtive environment, behavior, social structure, responses perceived threats. Some species respond well to beingto humans, and other traits. These variations challenge left within typical social groups or familiar surround-the application and effectiveness of euthanasia meth- ings as long as possible prior to euthanasia to minimizeods for the many different species. The efficacy of these anxiety.methods can be further limited by the circumstances Best practice for many captive wild animal speciesunder which euthanasia is performed. Consequently, includes a multistep approach, beginning with admin-the best means of terminating an animal’s life might istration of a sedative or anesthetic to relieve anxietynot strictly conform to the definition of euthanasia. and pain. For wild animals in captivity, physical and/orFor nondomestic captive or free-ranging animals, the chemical restraint is usually required before euthana-methods selected will often be situation specific, as a sia can be performed. Physical restraint is appropriatemeans of minimizing potential risks to the animal’s when skilled staff, facilities, suitable equipment, andwelfare and personnel safety. In addition, challenges as- the animal’s characteristics allow rapid immobilizationsociated with disposal of the remains of animals with with minimal distress.577 References should be consult-drug residues that have been addressed in the section ed for appropriate doses of anesthetics and anxiolyticsof the document on Dispoal of Remains (eg, second- and preferred routes of administration.424,578–580 Animalsary toxicity, environmental contamination, and other can be premedicated via IM injection and/or orally. In-topics) are relevant to disposal of the remains of non- travenous administration of drugs is generally difficultdomestic animals, particularly under field conditions. without physical or chemical restraint. Chamber deliv-Given the complexity of issues that euthanasia of non- ery of inhaled agents having little odor, such as sevo-domestic animals presents, personnel are encouraged flurane, allows for induction of anesthesia in smallerto consult references on anatomy, physiology, natural species with minimal stress. Injectable anesthesia canhistory, husbandry, and other disciplines that will aid be momentarily painful or discomforting during or im-in understanding how various methods may impact an mediately after administration due to a combination ofanimal’s euthanasia experience.52,53,132,575,576 Consulta- volume, formulation, and route of administration, astion with experienced colleagues is recommended, par- well as the distress associated with physical restraint.ticularly when novel circumstances and/or species are The advantages and disadvantages of administeringencountered. anxiolytics, anesthetics, or other drugs and applying Animals may become distressed due to physi- physical restraint should be balanced against the ben-cal discomfort, anxiety in atypical social settings and efit of providing a swift death to end suffering. Researchphysical surroundings, pheromones or odors from is needed to improve the euthanasia options availablenearby or previously euthanized animals, and the pres- for some taxonomic groups and circumstances.ence of humans. In addition, human safety, observers’perceptions, availability of trained personnel, potential S7.2 CAPTIVE INVERTEBRATESinfectious disease concerns, conservation and other Invertebrates comprise more than 95% of the ani-population objectives, regulatory oversight that may be mal kingdom’s species and include unrelated taxonomicspecies specific, available equipment and facilities, op- groups: spiders (Araneae),581 centipedes and millipedestions for disposal, potential secondary toxicity, research (Myriapoda), insects (Hexapoda),582 and many others.objectives, and other factors must be considered. Hu- Terrestrial invertebrates play important roles in labora-man safety is of utmost importance for all euthanasia tory research, as display animals, and as companions inprocedures, and appropriate protocols and equipment the home. Despite their varied roles, limited guidance(including supplies for addressing human injury due is available on appropriate methods by which inverte-to animal handling or exposure to immobilizing drugs) brates may be euthanized.63,132,583–585 This is due, in part,must be available prior to handling animals.577 Laws to a lack of coverage under animal welfare regulationsand regulations pertaining to the species being eutha- applicable to animals used for research and other pur-nized, the euthanasia methods employed, and disposal poses in the United States and other countries.574,586 Di-of the remains must be followed. versity in anatomic, physiologic, and other characteris- Euthanasia of captive wild animals requires con- tics limits generalizations across taxa.281 Of particularsideration of basic stewardship, physiologic and behav- relevance are differences in innervation and circulatoryioral variation, and relief from pain and anxiety. Man- systems, some of which do not have close corollariesagement can be guided by the physical and social set- in familiar vertebrate systems. This creates challengesting the animal is in (eg, small enclosures, seminatural for developing humane means of terminating inverte-conditions), the animal’s temperament, seasonal factors brates’ lives.(eg, reproductive stage, physical condition), and differ- While there is ongoing debate about invertebrates’ences from similar domestic species. Appropriate han- abilities to perceive pain or otherwise experience com-dling and modifying the animal’s physical and social promised welfare, the Guidelines assume that a conser-environment to minimize distress, as well as adminis- vative and humane approach to the care of any creaturetration of anxiolytics, are recommended. Provision of is warranted and expected by society. Consequently,preferred bedding, temperature, humidity, and security euthanasia methods should be used that minimize theAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 75
  • 76. potential for pain or distress. Most commonly usedmethods involve terminal anesthesia, followed by phys- S7.3 CAPTIVE AMPHIBIANS AND REPTILESical destruction of the nervous system, to assure lackof sensory perception and death of the animal. The di- S7.3.1 Anatomy and Physiologyversity of invertebrate taxa may require equally diverse Amphibians and reptiles include caecilians (or-approaches to euthanasia. der Gymnophiona), frogs (order Anura), salamanders (order Caudata), snakes (suborder Serpentes), lizardsS7.2.1 Acceptable Methods (suborder Lacertilia), crocodilians (order Crocodilia), and turtles and tortoises (superorder Chelonia). OnceS7.2.1.1 Noninhaled Agents again, these taxonomic groups differ substantially ana- Injectable agents—While there is little dosing or out- tomically and physiologically from each other, as wellcome data in the peer-reviewed literature, an overdose as from mammals. Of particular concern for amphib-of pentobarbital or similar agent, at a dose equivalent ians and reptiles are differences in metabolism and highto that used for other poikilotherm vertebrates (piscine, tolerances to hypoxia, as compared with mammals, thatamphibian, or reptilian) on a weight-to-weight basis will limit the effectiveness of methods based on anoxia. Ingenerally suffice. Ideally these agents will be injected di- addition, consistent access to the vasculature can berectly into the circulating hemolymph. However, because challenging and, therefore, many conventional meth-many invertebrates have an open circulatory system, true ods of euthanasia are less efficacious for these species.intravascular application can be difficult if not impos- Because it is often difficult to confirm that an amphib-sible. In such cases an intracoelomic injection would be ian or reptile is dead, the application of two or more eu-warranted unless otherwise contraindicated. Premedica- thanasia procedures is usually recommended.552,589–591tion with an injectable or inhaled agent may facilitate ad- Our understanding of amphibians’ and reptiles’ministration of barbiturate overdoses. nociception and responses to stimuli is incomplete; therefore, many recommendations for minimizing painS7.2.2 Acceptable With Conditions Methods and distress are extrapolated from information avail- able about mammals. Where uncertainty exists, erringS7.2.2.1 Inhaled Agents to proactively alleviate potential pain and suffering is Inhaled anesthetics—Overdose of an inhaled anes- recommended as an appropriate approach to eutha-thetic is acceptable with conditions for terrestrial in- nizing amphibians and reptiles. Consulting multiplevertebrates where injectable agents are not available. references on amphibian and reptile euthanasia is ad-Because confirming death of many species of inverte- vised as a means of identifying methods that are mostbrates can be difficult, subsequent use of an adjunctive appropriate for a given species and set of circumstanc-method of euthanasia is recommended. es.166,312,401,552,553,589–591 Carbon dioxide—Carbon dioxide may be useful for S7.3.2 Restrainteuthanasia of some terrestrial invertebrates, but addi- Physical restraint—Manual restraint is possible fortional information is needed to confirm its efficacy. many species. Equipment may be required for restraint of some species in some situations (eg, venomous spe-S7.2.2.2 Physical and Chemical Methods cies). Multiple people may be required for larger spe- Physical (eg, boiling, freezing, pithing) and chemi- cies, and at least one additional person should be avail-cal (eg, alcohol, formalin) methods act by destroying able for emergencies. Large animals may represent athe brain or major ganglia. Physical and chemical meth- proportionately greater risk for personnel.ods should be applied adjunctively, following pharma-ceutical or other chemical induction of anesthesia, non- Chemical restraint—Chemical restraint may beresponsiveness, or presumptive death. These methods useful in some situations, particularly for venomous orare not considered to be humane as sole methods of large animals where human safety would be compro-euthanasia.583,584,587,588 mised by manual restraint. Chemical restraint at high doses may serve as a first or preparatory step of eutha- Pithing—This method requires detailed anatomic nasia in some situations.knowledge of the species in question. S7.3.3 Verification of DeathS7.2.3 Unacceptable Methods Methods used to verify death in mammalian spe- Because information on the physiologic responses cies, such as auscultation, ECG, Doppler ultrasound,of invertebrates to many methods of euthanasia is not or pulse oximetry, can be used for amphibians and rep-available at this time, comments regarding unacceptable tiles, but it is important to remember that amphibianmethods of euthanasia are limited to those that should and reptilian hearts can beat even after brain death.not be applied as sole methods of euthanasia (see com- Death should always be confirmed by physical inter-ments under Acceptable With Conditions Methods). vention.S7.2.4 Developmental Stages of Invertebrates S7.3.4 Acceptable Methods Recommendations for euthanasia of the develop-mental stages of invertebrates are currently not available. S7.3.4.1 Noninhaled Agents Injectable agents—Venous access for administra-76 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 77. tion of euthanasia agents can be challenging for somespecies. Intracoelomic, subcutaneous lymph spaces, S7.3.5 Acceptable With Conditions Methodsand lymph sacs are acceptable routes of administration.Direct injection into the brain through the parietal eye, S7.3.5.1 Inhaled Agentswhile under anesthesia, has been described for some Inhaled anesthetics—Inhaled anesthestics are ac-lizard species.592 ceptable with conditions when they are more practical Sodium pentobarbital (60 to 100 mg/kg of body than the previously mentioned acceptable methods,weight) can be administered IV, intracoelomically, in and where the limitations of this method are under-the subcutaneous lymph spaces, or in the lymph sacs, stood and addressed. Many reptiles and amphibians arealthough doses vary by species.593 Doses as high as capable of breath holding and shunting of their blood,1,100 mg/kg (500 mg/lb) of sodium pentobarbital with which permits conversion to anaerobic metabolism forsodium phenytoin administered intracoelomically may survival during prolonged periods of anoxia (up to 27be required for euthanasia of some species such as X hours for some species).601–606 Because of this, inductionlaevis.312 Time to effect may vary, with death occurring of anesthesia and time to loss of consciousness may beinstantaneously or up to 30 minutes later.77,552,589–591,594 greatly prolonged when inhaled agents are used. DeathBarbiturates are best administered intravascularly to may not occur even with prolonged exposure.552,589–591minimize the discomfort upon injection.595 However, Lizards and most snakes do not hold their breath to thewhere intravascular administration is not possible or same extent as some of the chelonians, and are there-its benefits are outweighed by distress imposed by ad- fore more likely to have a clinical response to inhaledditional restraint, pain from alternate methods, risk to agents. Regardless of the species or taxonomic group,personnel, or other similar reasons, intracoelomic ad- death must be verified prior to terminating the use ofministration is an acceptable route for administration the inhaled agent, or a second, guaranteed lethal proce-of barbiturates. dure (eg, decapitation) should be performed to ensure Dissociative agents such as ketamine hydrochlo- death.ride or combinations such as tiletamine and zolazepam; Inhaled anesthetics are effective, have a moderatelyinhaled agents; and IV administered anesthetics, such rapid onset, appear to induce a painless death, can max-as propofol, or other ultra–short-acting barbiturates, imize use of the euthanized animal for analytic studies,may be used for poikilotherms to induce rapid general and can minimize the need for animal handling. Cave-anesthesia and subsequent euthanasia, although appli- ats include that inhaled anesthetics are most suitablecation of an adjunctive method to ensure death is rec- for smaller species, animals may experience an excita-ommended. tion phase prior to becoming anesthetized, they present environmental pollution and occupational hazard con- External or topical agents—Buffered tricaine meth- cerns, some are irritants or are perceived as noxious,anesulfonate (MS 222) may be administered via water and amphibians and reptiles may be resistant to theirbaths (amphibians), or injected directly into the lymph action because of breath holding.sacs (amphibians) or the coelomic cavity (amphibiansand reptiles).596–599 Prolonged immersion (as long as 1 Carbon dioxide—Carbon dioxide may be consideredhour) may be required for 5 to 10 g/L water baths.312,593 for euthanasia of amphibians and reptiles if alternateTricaine methanosulfonate does not create histopatho- methods are not practical and where the limitations oflogic artifacts.596 See the Noninhaled Agents section of this method are understood and addressed.401,552,553,589–591the Guidelines for additional information. Due to the potential lack of response to this method Benzocaine hydrochloride, a compound similar to by many species and the requirement for a prolongedMS 222, may be used as a bath or in a recirculation exposure time, other methods are preferable. Death bysystem at concentrations Ն 250 mg/L or applied topi- CO2 must be verified, and preferably, assured by appli-cally to the ventrum as a 7.5% or 20% gel for euthanasia cation of a secondary lethal procedure.of amphibians.600 A dose of 182 mg/kg of benzocainegel (20% concentration, 2.0-cm X 1.0-mm application) S7.3.5.2 Physical Methodshas been reported as effective for euthanasia of adult Penetrating captive bolt or firearm—CrocodiliansX laevis.312 Pure benzocaine is not water soluble and and other large reptiles can be euthanized by a pene-should be avoided for anesthesia or euthanasia because trating captive bolt or gunshot (free bullet) delivered toit requires the use of acetone or ethanol solvents, which the brain.166 Line drawings of the head of various am-may be irritating to tissues.310 phibians and reptiles, with recommended locations for In general, these noninhaled agents are highly ef- captive bolt or firearm projectile penetration, are avail-fective, their onset of action is rapid, and they are ap- able.401 Refer to ballistics details in the Physical Meth-plicable across a range of species and sizes of animals. ods section and experts for more information on selec-However, general anesthesia may be required prior to tion and use of firearms.administration, some require IV administration for ves- These methods are moderately rapid (allowing forsels that may be difficult to access, they may produce restraint), are applicable across a wide range of speciesundesirable tissue artifacts, a controlled substance li- and sizes, and leave no environmental residues othercense is required for barbiturates and some other prod- than lead (in the case of free bullet), which can be se-ucts, and there may be environmental pollution and questered. However, size-appropriate equipment and ap-toxicity concerns depending on method of disposal of propriately trained personnel are required, violent mus-the remains. cle contractions can occur following their application,AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 77
  • 78. and they may be aesthetically unpleasant for onlookers. acceptable for captive amphibians and reptiles that are Manually applied blunt force trauma to the head— unresponsive to stimuli because of disease or the appli-This method is acceptable with conditions, when other cation of other euthanasia methods, or in cases whereoptions are unavailable, as long as it is performed by other routes are not possible.well-trained and skilled personnel and if an adjunctive Neuromuscular blocking agents may be used formethod, such as decapitation or pithing, is promptly routine anesthetic procedures of crocodilians and someapplied to ensure death.52,132,589,591 Further research is other taxa and are, therefore, considered acceptableneeded to clarify methods, taxa, and size ranges where with conditions for restraint of reptiles if given imme-this method is effective and humane. diately prior to administration of a lethal agent. These agents are not acceptable as a sole means of euthanasia. Rapid freezing—Reptiles and amphibians can be Injectable agents such as lidocaine hydrochloride,euthanized by rapid freezing when it results in immedi- potassium salts, or magnesium salts may be useful as anate death. Based on rodent models, it is likely that this adjunctive method to prevent recovery.591can be achieved by placing animals < 4 g (0.1 oz) in Perfusion with fixative of a deeply anesthetized an-liquid N2.52 The technique should not be used for spe- imal can be used to euthanize amphibians and reptilescies that have adapted freeze tolerance strategies, as this when scientifically justified.method may not result in instant death.607 Placement ofanimals Ն 4 g in liquid N2 or other uses of hypothermia S7.3.9 Destruction of Viable Eggsare not acceptable. Little information is available on the sensory ca- pacity of amphibians and reptiles at the egg stage ofS7.3.6 Adjunctive Methods development.52 Freezing is likely appropriate for newly Decapitation—After animals have been anesthe- oviposited eggs, as would be methods of macerationtized, decapitation using heavy shears or a guillotine that result in instantaneous death. Later stages may beis effective for some species. It has been assumed that destroyed using methods that are acceptable for adultstopping blood supply to the brain by decapitation animals. More research needs to be done to determinecauses rapid loss of consciousness. However, because the most appropriate methods for disposing of live eggs.the CNS of reptiles and amphibians is tolerant to hy-poxic and hypotensive conditions,401 decapitation must S7.4 CAPTIVE NONMARINE MAMMALSbe followed by pithing or another method of destroyingbrain tissue.589,591,595 Decapitation should only be per- S7.4.1 General Considerationsformed as part of a 3-step euthanasia protocol (inject- The anatomic, physiologic, behavioral, and sizeable anesthetic, decapitation, pithing). variations of nondomestic mammals far exceed those of their domestic counterparts. This presents challenges Pithing—Pithing can be used as a second-step eu- for the application of conventional methods of eutha-thanasia method in unconscious animals when per- nasia and the recognition of anxiety and pain. Differ-formed by properly trained individuals.589,591 The pithing ences from similar domestic species must be recognizedsite in frogs is the foramen magnum, and it is identified and addressed as thoroughly as practical when prepar-by a slight midline skin depression posterior to the skull, ing for and performing euthanasia.midline between the eyes, with the neck flexed.552,590 In zoos or other captive settings, euthanasia of wildlife is typically performed in the presence of staffS7.3.7 Unacceptable Methods members who are responsible for caring for these ani- Hypothermia—Hypothermia is an inappropriate mals. Consequently, sensitivity to the meaning and val-method of restraint or euthanasia for amphibians and ue to caregivers of animals in this kind of setting is im-reptiles unless animals are sufficiently small (< 4 g)52 portant. This can be addressed, in part, with attentionto permit immediate and irreversible death if placed to stewardship, and relief from pain and anxiety priorin liquid N2 (rapid freezing).589,591,595 Hypothermia re- to administration of a euthanasia method. Most eutha-duces amphibians’ tolerance for noxious stimuli608,609 nasia procedures should include the use of inhaled orand there is no evidence that it is clinically efficacious injectable anesthetics to achieve unconsciousness, fol-for euthanasia.610 In addition, it is believed that freezing lowed by use of an approved method to end life.can result in the formation of ice crystals in tissues that In some cases animals may experience intoler-may cause pain.52,401 Consequently, because amphibians able suffering, or the situation may not allow for idealand reptiles lack behavioral or physiologic means of stewardship as a prelude to the act of euthanasia. Thesedemonstrating pain or distress while hypothermic, gen- situations typically require a more direct approach toeralized prohibitions on hypothermia for restraint or limit how much an animal is allowed to suffer. Sucheuthanasia are appropriate. Localized cooling in frogs situations also require a brief explanation to personnel,may reduce nociception, but this localized effect is not where possible, as well as a more complete explanationappropriately applied to the whole body as a part of eu- of the choice of method subsequent to completion ofthanasia procedures.611 Freezing of deeply anesthetized the procedure. Preparing staff ahead of time to be cog-animals may be justified under circumstances where nizant of the possibility of these kinds of situations willhuman safety could be compromised.612 likewise help to better prepare for situations where a more ideal procedure is not feasible.S7.3.8 Special Cases and Exceptions Alternate approved methods of euthanasia might Intracardiac administration of euthanasia agents is be applicable if an animal is anesthetized prior to eu-78 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 79. thanasia. Any candidate method not specifically men- other anesthetics may be administered IV or IM for eu-tioned in the text that follows should be evaluated con- thanasia when animal size, restraint requirements, orceptually to address good stewardship principles prior other circumstances indicate these drugs are the bestto its use. option for euthanasia. Following euthanasia, verification of death is im- Intramuscular administration of opioids is advan-portant. Methods that can be used for verification of tageous when other routes of administration are notcessation of cardiac function include, but may not be available. Opioids tend to have a rapid onset of ac-limited to, palpation for a pulse in an appropriate ana- tion, and the volume of drug to be administered maytomic location based on species, auscultation with a be smaller than for other agents. There are also disad-stethoscope, and use of Doppler ultrasound. vantages associated with administering an overdose of opioids, including requirements for DEA licensing andS7.4.2 Restraint veterinary oversight for extralabel use, risks to human Physical restraint—Manual restraint is possible for safety if exposure to drugs occurs, and the potential formany species. Nets or other equipment may be appro- secondary toxicity if tissues are consumed.priate for smaller species that do not pose an excessiverisk for personnel. For the largest species (hoofstock S7.4.4 Acceptable With Conditions Methodsand megavertebrates), chutes or other equipment mayprovide sufficient restraint for IM or IV administration S7.4.4.1 Inhaled Agentsof anesthetics and/or anxiolytics. Brief restraint fol- Inhaled anesthetics—Inhaled anesthestics are ac-lowed by IV administration of a euthanasia agent may ceptable with conditions when they are more practicalbe possible as an approach to euthanasia in some situ- than acceptable methods, and where the limitations ofations. However, administration of a preanesthetic or this method are understood and addressed. Inhaled an-sedatives before administration of a euthanasia agent esthetics may be administered via face mask or cham-should be the default in most cases. bers. Placing an animal’s entire crate into a chamber will allow anesthesia to be induced with the least amount of Chemical restraint—Chemical restraint may be use- distress. As discussed in the Inhaled Agents section offul in some situations, particularly for dangerous ani- the Guidelines, agents with minimal odor are preferred.mals where human safety would be compromised with Inhaled anesthetics have a moderately rapid onsetmanual restraint, as well as to reduce unnecessary stress of action, do not appear to cause pain on administra-and discomfort for the animal(s). Chemical restraint at tion, maximize the availability of the animal’s remainshigh doses may serve as the first step of euthanasia in for analytic studies, and can be applied with minimalsome situations.424,578–580 handling of the animal. They also, however, have some disadvantages in that they are most suitable for smallerS7.4.3 Acceptable Methods species, some are irritants or are perceived as noxious, animals can experience an excitation phase prior to in-S7.4.3.1 Noninhaled Agents duction of anesthesia, and they may present environ- Barbiturates—Barbiturates may be administered mental pollution and occupational safety concerns.IV or IP. Intracardiac administration must be limitedto animals that are unconscious due to disease or the Carbon monoxide, carbon dioxide, and inert gases—effects of anesthetics. Onset of action is slower with These agents are acceptable with conditions for appli-IP administration and premedication with anesthetics cation where animal welfare and pragmatic concernsmay reduce discomfort due to tissue irritation. Barbitu- warrant their use and risks to personnel safety can berates are best administered intravascularly to minimize addressed. For more information, please consult thediscomfort upon injection.595 However, where intravas- Guidelines section on Inhaled Agents.cular administration is not possible or its benefits areoutweighed by distress imposed by additional restraint, S7.4.4.2 Physical Methodspain from alternate methods, risk to personnel, or other Penetrating captive bolt or firearm—Use of a pen-similar reasons, IP administration is an acceptable route etrating captive bolt or firearm (free bullet) may befor administration of barbiturates. appropriate for some species as a first step or adjunct Barbiturates are highly effective as euthanasia agents, method of euthanasia, when there is species-specifichave a rapid onset of action, and are applicable across a knowledge of target sites and safety considerations canwide range of species and sizes of animals. However, they be met.do have drawbacks, including that individuals must be Advantages of these methods are that they aretrained to correctly administer injections, general anes- moderately rapid (considering application of any need-thesia or sedation with injectable or inhaled agents may ed restraint), they may be relatively easily implementedbe required prior to their administration (depending on under various conditions, they are applicable across athe animal and the situation), they can produce unde- wide range of species and sizes, and they leave no en-sirable tissue artifacts, a controlled substance license is vironmental residues (other than lead, which may berequired for their acquisition, and environmental pollu- sequestered). There are some disadvantages in that theytion and toxicity may be of concern depending on the require appropriate, well-maintained equipment andmethod used to dispose of animal remains. well-trained personnel, they are potentially aestheti- cally displeasing for observers, and they present safety Nonbarbiturate anesthetic overdose—Opioids and risks for personnel associated with the keeping and useAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 79
  • 80. of firearms. Refer to ballistics details in the section on sea otter (a large mustelid) with small pinnipeds: (1)Physical Methods and experts for more information on pinnipeds, (2) odontocetes, (3) mysticetes, and (4) siri-selection and use of firearms. nids. Methods addressed under methods of euthanasia for captive mammals (nonmarine species) are applica-S7.4.5 Adjunctive Methods ble to polar bears, and will not be addressed in this sec- Potassium chloride—Potassium chloride can be tion. Sizes of the animals vary dramatically among andadministered IV or intracardially to stop the heart of within these groups and each group should minimallyanimals that are deeply anesthetized or unconscious. be divided into subgroups by size (large and small).Potassium chloride does not create artifacts that can Recommendations for euthanasia of marine mammalsinterfere with histopathologic examination and, there- in managed care facilities differ from those used forfore, its application may be appropriate when accurate free-ranging marine mammals, because of differencespostmortem diagnostic or research results are impor- in environment and facilities, restraint capabilities, andtant. Potassium chloride may also be used adjunctively personnel and observers.for large animals that are first anesthetized with bar-biturates, particularly where volume of administration S7.5.1 Acceptable Methodsis a limitation. In many cases significant agonal reflexactivity can be avoided where barbiturates are admin- S7.5.1.1 Noninhaled Agentsistered prior to administration of potassium chloride. Intravenous administration of barbiturates and their derivatives can be a rapid and reliable method of Exsanguination—Exsanguination may be useful as euthanasia for small pinnipeds, small odontocetes, anda secondary or tertiary method to ensure death. The sirinids. Intraperitoneal administration is also accept-aesthetics of this procedure and its acceptance by per- able where intravascular administration is not possiblesonnel must be considered in its application. or is outweighed by distress from the requirement of additional restraint, pain from alternate methods, risk Cervical dislocation or decapitation—Applied to to personnel, or other similar reasons, although tissuesmall mammals and birds, this method may be useful irritation and variable absorption rates must be con-as an adjunct or as a first-step method of euthanasia. sidered. Safe and effective IV administration of theseA paucity of data for wildlife and the potential for in- agents may also be possible in anesthetized, moribund,terspecies variation creates challenges for establishing or unconscious large pinnipeds and in large odon-specific size recommendations. However, based on do- tocetes. For the largest odontocetes, drug dilution inmestic animals, manual cervical dislocation may be ap- large volumes may limit the effectiveness of euthanasiapropriate for birds < 3 kg (6.6 lb), rodents < 200 g, and agents administered IV. Intracardiac administration israbbits < 1 kg (2.2 lb).599 A secondary method such as acceptable only in anesthetized, moribund, or uncon-decapitation or exsanguination should be employed to scious animals.ensure death when feasible. The advantage of using barbiturates is that death is usually rapid. Unfortunately, voluntary peripheral Thoracic compression—Thoracic compression may vasoconstriction by cetaceans or hypovolemic shockbe useful in rare circumstances in animals that are deep- may limit access to peripheral veins. There is also aly anesthetized or otherwise unconscious, or as a final, risk of injury for personnel attempting venipuncture ifconfirmatory step when the animal’s status is uncertain. animals are not restrained. Furthermore tissue residues can present challenges for disposal of the animal’s re-S7.4.6 Unacceptable Methods mains and personnel are responsible for ensuring that Methods that are classified as being unacceptable secondary toxicity does not occur.for use in comparable domestic species are unaccept- Intramuscular administration of sedatives or anes-able for use in wild mammals that are not deeply anes- thetics may be required to immobilize large, anxious, orthetized. fractious animals to ensure animal and personnel safety prior to administration of IV euthanasia agents. AgentsS7.4.7 Embryos, Fetuses, and Neonates that have successfully been used alone or in combina- Euthanasia of embryos, fetuses, and neonates tion for this purpose include tiletamine-zolazepam,should be conducted using guidelines appropriate for ketamine, xylazine, meperidine, fentanyl, midazolam,taxonomically similar domestic mammals. diazepam, acepromazine, and etorphine.613 Veterinar- ians should be aware that administration of anestheticsS7.5 CAPTIVE MARINE MAMMALS or sedatives in fat layers can result in prolonged time to Due to their unique anatomic and physiologic ad- effect and diminished depth of sedation and anesthesia.aptations for aquatic environments, the large size of In addition, tissue residues, particularly when ultrapo-some species, and the challenges associated with per- tent opioids are administered, need to be consideredforming euthanasia under typical circumstances, ma- when disposing of the animal’s remains.rine mammals are considered separately from othermammals. To facilitate making appropriate recommen- S7.5.2 Acceptable With Conditions Methodsdations regarding euthanasia, marine mammals havebeen divided into physiologically and anatomically dis- S7.5.2.1 Inhaled Agentstinct groups. These groups follow taxonomic lines to Inhaled anesthetics (eg, halothane, isoflurane,some extent, though it is appropriate to consider the sevoflurane, methoxyflurane, enflurane) are uncom-80 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 81. monly used to euthanize marine mammals because to the euthanasia of wildlife. In the United States, man-these animals’ ability to breath- hold means that ex- agement of wildlife is primarily under state jurisdiction.tended periods of physical restraint are necessary for However, some species (eg, migratory birds, endangeredtheir administration. Extended restraint generally pos- species, marine mammals) are protected and managedes unacceptable risks and stress for the animal and for by federal agencies or through collaboration betweenpersonnel unless the animal is substantially debilitated, state and federal agencies. Within the context of wildlifesedated, or anesthetized. Use of inhaled agents may be management, personnel associated with state and federalappropriate for small pinnipeds after administration of agencies and Native American tribes may handle or cap-an injectable sedative or anesthetic under circumstanc- ture individual animals or groups of animals for variouses where acceptable methods are not practical or appro- purposes, including research. During the course of thesepriate for other reasons. management actions, individual animals may become in- Inhaled agents present some advantages in that jured or debilitated and may require euthanasia; in otherthey do not require phlebotomy skills and may present cases, research or collection protocols dictate that someminimal concern for tissue residues.171 Disadvantages of them be killed. Sometimes population managementinclude that they are expensive, require an extended requires the lethal control of wildlife species. And, thedelivery time with associated risks of distress and in- public may identify and/or present individual animalsjury for animals and personnel, and may be noxious to to state or federal personnel because they are orphaned,the animal. sick, injured, diseased (eg, rabid), or becoming a nui- sance. Another aspect of wildlife management is reha-S7.5.2.2 Physical Methods bilitation of orphaned or injured wildlife. For the most Physical methods, although used to euthanize free- part, wildlife rehabilitation is done by private citizensranging marine mammals, will generally not be used and requirements for handling these animals vary byon captive mammals due to limited efficacy for these state and species.species, risk for personnel, and aesthetics. S7.6.2 Special ConsiderationsS7.6 FREE-RANGING WILDLIFE The primary factor influencing methods selected for euthanasia of free-ranging wildlife is lack of controlS7.6.1 General Considerations over the animal. In addition, some species may be too Free-ranging wildlife are present in all habitats large to effectively euthanize by conventional means.across North America including fresh and salt water. Marine mammals are of particular concern due to theirWildlife includes representatives of all known animal large size and the lack of standardized equipment andtaxa, but for the purpose of the Guidelines, will be re- techniques (see Free-Ranging Marine Mammals forstricted to amphibians, reptiles, birds, and mammals, more information). Other species, such as reptiles,including some feral and exotic species. Wildlife are en- may be refractory to conventional euthanasia agents.joyed and used by people in a number of ways includ- The potential for secondary toxicity and environmentaling nonconsumptive uses (wildlife viewing, bird watch- hazards associated with the remains of animals eutha-ing, bird feeding) and legal harvest (hunting, fishing, nized by chemical means are of substantial concern, ascommercial take). Varied interests and perspectives can is disposal of large or numerous animal remains. There-influence what methods are used to terminate the lives fore, while some methods described in the taxonomi-of free-ranging wildlife.614 This section of the Guide- cally based sections for nondomestic animals may belines updates and expands upon previous editions by useful for euthanizing free-ranging wildlife, their appli-recognizing an inherent lack of control over free-rang- cability will vary.ing wildlife, accepting that firearms may be the most Given that close human contact is stressful and dif-appropriate approach to their euthanasia, and acknowl- ficult to achieve for most free-ranging animals, theseedging that the quickest and most humane means of animals may have to be euthanized or immobilizedterminating the life of free-ranging wildlife in a given from a distance. In some cases (eg, suburban areas),situation may not always meet all criteria established discharge of a firearm is illegal, is considered a seri-for euthanasia (ie, distinguishes between euthanasia ous threat to human safety, or may be inappropriate forand methods that are more accurately characterized as other reasons. Consequently, free-ranging animals mayhumane killing). need to be killed quickly and efficiently in ways that Because of the variety of situations that may be may not fulfill the criteria for euthanasia established byencountered, it is difficult to strictly classify methods the POE.for termination of free-ranging wildlife as acceptable, Remotely delivered chemical immobilization mayacceptable with conditions, or unacceptable. Further- be required when wildlife cannot be captured. If a free-more, classification of a given method as a means of eu- ranging animal is within an acceptable range, trainedthanasia or humane killing may vary by circumstances. individuals may use species and situation-specific an-These acknowledgments are not intended to condone esthetic agents and remote injection equipment toa lower standard for the humane termination of wild- anesthetize that animal to allow handling. Once anes-life. The best methods possible under the circumstanc- thetized, many wildlife species can be euthanized viaes must be applied, and new technology and methods methods similar to those applied to domestic or captivedemonstrated to be superior to previously used meth- wild animals of similar species and size. Other tech-ods must be embraced. niques used in wildlife management for trapping or Multiple federal, state, and local regulations apply capturing animals may also be applied to allow someAVMA Guidelines for the Euthanasia of Animals: 2013 Edition 81
  • 82. degree of control over the animal. which euthanasia of free-ranging wildlife may need to Care must be taken to prevent secondary intoxi- be conducted, choice of the most humane method willcation of animals or people during disposal of the re- vary by species, situation, and individual animal. Con-mains of free-ranging wildlife that contain residues of ditions specified for use of various methods in previ-euthanasia agents. This is a legal requirement that of- ous sections will generally apply to free-ranging wild-ten requires deep burial, incineration, or rendering. In life, but may be modified according to circumstances toother situations, however, natural decomposition may minimize animal distress and pain, as well as emotionalbe desirable. Use of gunshot can minimize concerns for impact and physical risks to personnel.secondary toxicity, with the exception of lead ballistics.Alternatives to lead ballistics are recommended where S7.6.3.1 Acceptable Methodspossible. Although not typically a part of wildlife manage- S7. Noninhaled Agentsment programs, disease outbreaks or overpopulation Chemical methods of euthanasia applicable to free-may require culling or large-scale killing of animals. In ranging wildlife include overdoses of injectable anes-addition to selecting the most appropriate methods for thetic agents (including barbiturates), T-61, or otherminimizing spread of infectious agent, protecting ani- agents that are listed as acceptable for domestic animalsmal welfare, and protecting the environment, such situ- or captive wildlife. Premedication with an injectable orations must consider the concerns and perceptions of inhaled agent may reduce animal distress and/or hu-the general public, as well as impacts upon personnel man safety risks, under some circumstances.who are directly involved in culling, killing, or euthana-sia. Detailed information about depopulation methods S7.6.3.2 Acceptable With Conditions Methodsis beyond the scope of this document, but will be madeavailable in the AVMA Guidelines for the Depopulation S7. Inhaled Agentsof Animals. Inhaled anesthetics—Inhaled anesthetics are accept- Research objectives may limit the use of some eu- able with conditions for euthanasia of avian and mam-thanasia agents or methods for wildlife species. Never- malian wildlife species when these methods are moretheless, termination of life still dictates that the most practical than acceptable methods, and where the limi-humane, rather than the most convenient, methods be tations of this method are understood and addressed..used to meet the study’s objectives. Smaller species that can be confined in enclosed con- Within the context of wildlife rehabilitation, eu- tainers can be euthanized using open-drop methods ofthanasia of individual animals must be considered if a administration.622 Larger species may be restrained forfully functional animal cannot be returned to the wild, face-mask administration, when animal distress associ-if the release of such animals would pose a threat to the ated with restraint can be minimized. Portable equip-health of the free-ranging wildlife population, or if no ment is available that can make these methods practi-alternatives for care or housing exist. While there are cal. Preference should be given to the use of alternatea limited number of nonreleasable animals that can be methods for taxa that can breath-hold for extended pe-used for educational or display purposes, most animals riods of time.that are determined to be unfit for release should be eu-thanized as soon as possible. Because most animals in Carbon dioxide, carbon monoxide, and other inertrehabilitation facilities are confined, adequate control gases—These agents, which are classified as being ac-through physical or chemical restraint can usually be ceptable with conditions for domestic animals, areachieved that will allow administration of euthanasia also acceptable with conditions for euthanasia of free-agents as described in the taxonomically based sections ranging wildlife. Conditions that must be met for usingfor nondomestic animals. these agents are similar to those for domestic animals.S7.6.3 Methods S7. Physical Methods Little published information is available regarding Gunshot is acceptable with conditions for eutha-appropriate methods for euthanasia of specific species nasia of free-ranging, captured, or confined wildlife,of free-ranging wildlife. Schwartz et al282 evaluated im- provided that bullet placement is to the head (targetedmobilization and euthanasia for white-tailed deer, Hy- to destroy the brain).575 Gunshot targeted to the heartman615 and Needham616 described euthanasia methods (chest) or to the neck (vertebrae, with the intent of sev-for captive or stranded marine mammals, and the eu- ering the spinal cord) presents challenges for accuratethanasia of waterfowl was described by Gullett617 and placement, but may be the best option for free-rangingFranson.265 Methods for euthanasia of wildlife in reha- or other settings where close approach is not possiblebilitation facilities have also been described.415 or where the head must be preserved for disease testing While multiple publications describe eutha- (rabies, Chronic Wasting, or other suspected neuro-nasia methods for domestic and nondomestic ani- logic diseases). Based on domestic animal models (seemals,52,53,63,132,575 as well as for wildlife under free-rang- section of the Guidelines addressing Farmed Animalsing conditions,618–621 their recommendations are incon- Used for Food and Fiber), gunshot to the chest or necksistent. Many conventional euthanasia techniques and may not result in rapid death and may be consideredmethods can be applied to free-ranging wildlife, if the humane killing, rather than euthanasia. In some envi-animals are sufficiently under the control of personnel. ronments (eg, urban and suburban areas), discharge ofHowever, because of the variety of conditions under a firearm may present a serious threat to human safety82 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 83. and may be inappropriate. Refer to ballistics details inthe Physical Methods section and experts for more in- S7.7.1 Acceptable Methodsformation on selection and use of firearms. S7.7.1.1 Noninhaled agentsS7.6.3.3 Adjunctive Methods Overdoses of injectable anesthetics can be used Potassium chloride—Potassium chloride may be to euthanize marine mammals under field conditions.administered IV or intracardially to stop the heart of Anesthetics that can be used alone or in combinationanimals that are deeply anesthetized or unconscious. include tiletamine-zolazepam, ketamine, xylazine, me-Administration of potassium chloride can also be pre- peridine, fentanyl, midazolam, diazepam, butorphanol,ferred for large animals when administered with barbi- acepromazine, barbiturates, and etorphine.613,624,625 In-turates, where volume of administration is a limitation. tramuscular administration of anesthetics may be re- quired to achieve restraint of conscious animals before Exsanguination—Bleeding may be used as an ad- personnel can safely perform euthanasia using inject-junctive method to ensure the death of animals that are able agents by an intravascular route. A clear under-anesthetized or otherwise unconscious. The aesthetics standing of species anatomy and use of sufficiently longof this procedure and its acceptance by personnel and needles are required to ensure that muscle, rather thanobservers should be considered. fat, is the site of injection. Injectable anesthetics may be administered by Cervical dislocation or decapitation—Applied to multiple routes. Mucocutaneous administration, viasmall mammals and birds, this method may be useful as the blowhole, can be an effective method that maxi-an adjunct or as a first-step method of euthanasia. A pau- mizes personnel safety.625 Intravenous administrationcity of data for wildlife and the potential for interspecies can be rapid and reliable for small pinnipeds, smallvariation create challenges for establishing specific size odontocetes, and sirinids. For larger animals, safe IVrecommendations. However, based on domestic animals, administration is generally limited to animals that aremanual cervical dislocation may be appropriate for birds anesthetized or unconscious. In addition, drug dilu-< 3 kg, rodents < 200 g, and rabbits < 1 kg.599 A sec- tion in large blood volumes of large odontocetes andondary method such as decapitation or exsanguination mysticetes may limit the effectiveness of IV adminis-should be employed to ensure death when feasible. tered agents. Intraperitoneal administration can be ef- fective for small marine mammals if sufficiently long Thoracic compression—Thoracic compression may needles are available to access the peritoneal cavity.be useful in rare circumstances in animals that are However, delayed absorption may limit the efficacy ofdeeply anesthetized or otherwise unconscious, or as a drugs administered via this route. Intracardiac admin-final, confirmatory method to ensure death when the istration is acceptable only in anesthetized, moribund,animal’s status is uncertain. or unconscious animals. This approach requires spe- cial, strong, and long needles to ensure that the heartS7.6.3.4 Unacceptable Methods can be accessed. Approaches to euthanasia that ignore recent ad- Advantages of injectable anesthetics are that theyvances in technology, and that do not minimize risks to act rapidly and personnel experienced with these meth-animal welfare, personnel safety, and the environment ods are readily available. Their administration is logis-for a particular set of circumstances, are unacceptable. tically simple and aesthetically acceptable, and public safety is relatively easy to secure. However, voluntaryS7.6.4 Embryos, Fetuses, and Neonates peripheral vasoconstriction by cetaceans or hypovole- Methods that are acceptable for euthanasia of do- mic shock may limit access to peripheral veins and fatmestic or captive wildlife species in developmental or layers must be bypassed for effective administration.neonatal stages are generally acceptable for euthanasia Large quantities of drug may be required to effectivelyof similar stages of free-ranging wildlife. euthanize large animals, and administration of single types of agents, such as α2 adrenergic receptor agonists,S7.7 FREE-RANGING MARINE MAMMALS can result in animals passing through aesthetically dis- Selecting a method of euthanasia for free-ranging pleasing and potentially unsafe excitation phases ofmarine mammals can be a substantial challenge be- anesthesia. There is a risk of injury for personnel at-cause of large body size, environmental constraints, and tempting to access veins if animals are not appropri-concerns for the safety of personnel. It can also be dif- ately restrained, and personnel may also face self-ad-ficult to determine when stranded marine mammals are ministration risks (especially for ultrapotent opioids).unconscious or dead.623 Currently available euthanasia Environmental contamination and scavenger exposuremethods generally have significant limitations that fail are possible due to residues in the animal’s remains.to meet aesthetic or other conventional standards foreuthanasia of marine mammals under field conditions, S7.7.2 Acceptable With Conditions Methodsparticularly for large animals. Nevertheless, the optionsavailable must be evaluated to identify the best option S7.7.2.1 Physical Methodsunder a given set of circumstances. Further research is Gunshot—Gunshot is acceptable with conditionswarranted to identify improved methods of euthanasia. for euthanizing small marine mammals when inject- able methods are not practical; conventional projectile ballistics are not recommended for use in large odonto-AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 83
  • 84. cetes or large mysticetes. References are available to as- Exsanguination—Exsanguination is inappropriatesist in identifying appropriate anatomic landmarks and as a sole method of euthanasia because it requires ancaliber of ballistics.348,626–630 excessively long time to death, is believed to produce Advantages of gunshot include a rapid death and anxiety associated with extreme hypovolemia, and isequipment that is generally readily available. Gunshot aesthetically displeasing to bystanders. It can, however,also poses minimal risk for other animals that may be used as an adjunctive method to ensure the death ofscavenge the animal’s remains. However, its efficacy is unconscious animals.630highly dependent on the knowledge, technical exper-tise, and experience of the operator. Associated noise a. Anthony R, University of Alaska Anchorage, Anchorage, Alaska:can distress other animals (especially in the case of Personal communication, 2011.mass strandings) and ricochet poses a risk to bystand- b. Tributame, TEVA Animal Health Inc, St Joseph, Mo. c. T-61, Intervet Canada Corp, Kirkland, QC, Canada.ers. Euthanasia by gunshot may also be aesthetically d. Finquel, Argent Laboratories Inc, Redmond, Wash.displeasing and emotionally distressing for personnel e. Tricaine-S, Western Chemical, Ferndale, Wash.and bystanders. Compliance with firearm regulations is f. Twitchell C, Roy LD, Gilbert FF et al. Effectiveness of rotating- ,also required. Refer to details for ballistics in the Physi- jaw killing traps for beaver (Castor Canadensis) (oral presenta-cal Methods section and experts for more information tion). North Am Aquat Furbearer Symp, Starkville, Miss, Mayon selection and use of firearms. 1999. g. Mays J. Euthanasia certification (slide presentation). Natl Anim Control Assoc Euthanasia Certification Workshop, Dayton, Manually applied blunt force trauma—In situations Ohio, September 2011.where other options are not available, a concussive h. Telazol, Fort Dodge Animal Health, Overland Park, Kan.blow to the head may be an effective method of eutha-nasia for small juvenile marine mammals.631 The advan- Referencestages of properly applied manual blunt force trauma are 1. Sandoe P Christiansen SB. Ethics of animal use. Chichester, West ,that it results in rapid death, no special equipment is Sussex, England: Wiley-Blackwell, 2008;1–14, 15–32, 49–66.required, and there is limited potential for secondary 2. Rollin BE. Animal agriculture and emerging social ethics fortoxicity for scavengers. However, the efficacy of manu- animals. J Anim Sci 2004;82:955–964.ally applied blunt force trauma is highly dependent on 3. DeGrazia D. Self-awareness in animals. In: Lurz R, ed. The phi-knowledge and experience of the operator and it is aes- losophy of animal minds. Cambridge, England: Cambridge Uni-thetically displeasing for personnel and observers. versity Press, 2009;201–217. 4. Thompson PB. Ethics on the frontiers of livestock science. In: Swain DL, Charmley E, Steel JW, et al, eds. Redesigning animal Implosive decerebration—Decerebration of large mys- agriculture: the challenge of the 21st century. Cambridge, Mass:ticetes and odontocetes can be effectively accomplished CABI, 2007;30–45.through the detonation of properly placed, shaped, and 5. Thompson PB. Getting pragmatic about farm animal welfare. In:dimensioned explosive charges.632,633 Advantages of this McKenna E, Light A, eds. Animal pragmatism: rethinking human-technique include a rapid death, limited potential for nonhuman relationships. Bloomington, Ind: Indiana University Press, 2004;140–159.exposure of scavengers to toxic residues, and protection 6. DeGrazia D. 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  • 98. Glossary Good Death: see EUTHANASIA. Harvest: The act or process of killing an animal forAcceptable: A method considered to reliably meet the food or other products. requirements of euthanasia. See EUTHANASIA. Humane Killing: Killing performed in a manner thatAcceptable With Conditions: A method considered minimizes animal distress, but may not meet the to reliably meet the requirements of euthanasia requirements of euthanasia due to situational con- when specified conditions are met. See EUTHANA- straints. SIA. Incineration: To burn completely, to ashes.Adjunctive Method: A method of assuring death that Insensible: See UNCONSCIOUS. may be used after an animal has been made uncon- Livestock: Domestic animals raised for use, consump- scious. tion, or profit, typically on a farm.Affect: The external expression of emotion. Mass euthanasia: see DEPOPULATION.Altricial: Immobile, blind, naked young animals (in- Nociception: Neuronal impulses generated by noxious cluding but not limited to birds and some rodents) stimuli, which threaten to, or actually do, destroy requiring parental care and feeding. tissue. Nociception can occur without consequen-Anesthesia, General: A method used to produce un- tial pain perception. consciousness. See UNCONCIOUSNESS. Pain: A sensation (perception) that results from noci-Animal: Any nonhuman animal (Kingdom: Animalia). ceptive nerve impulses reaching areas of the brainAversion: A desire to avoid or retreat from a stimulus. capable of conscious perception via ascending neu-Avian: Relating to birds. ral pathways.Captive Bolt: A device used to kill or stun animals Pithing: Physical destruction of the brain with a wire, where a tethered metal rod is discharged into the air jet, or rod. brain of the animal. Poikilotherm: An animal with a variable internal tem-Chick: A young bird. perature. These animals are generally ectothermic.Cremation: To incinerate a dead body. See INCINERA- Poult: A young fowl. TION. Poultry: Domestic fowl raised for meat or eggs, suchDepopulation: The killing of animals in large num- as chickens, turkeys, ducks, or geese. bers in response to an animal health emergency (eg, Precocious: Capable of a high degree of independent catastrophic infectious disease, mass intoxication, activity (ie, mobility, feeding) from birth. natural disaster) where all due consideration is Secondary Method: A euthanasia method employed given to the terminal experience of the animal, but subsequent to a primary method to ensure death of the circumstances surrounding the event are under- an unconscious animal before it can recover con- stood to be exigent and extenuating. Depopulation sciousness. See ADJUNCTIVE METHOD. may not meet the requirements of euthanasia due to Sedation: A state of CNS depression in which the ani- situational constraints. mal is awake but calm, and with sufficient stimuliDistress: The effect of stimuli that initiate adaptive re- may be aroused. sponses that are not beneficial to the animal—thus, Slaughter: Killing animals for the purposes of harvest- the animal’s response to stimuli interferes with its ing commodities such as meat or hides. welfare and comfort. Stress: The effect of physical, physiologic, or emo-Ectotherm: An organism that is dependent on envi- tional factors (stressors) that induce an alteration in ronmental heat sources for regulating its body tem- an animal’s homeostasis or adaptive state. perature. Stunning: Rendering an animal unconscious by use ofEustress: The effect of stimuli that initiate adaptive a physical, gas, or electrical method. responses that are beneficial to the animal. Suffocate: To kill by preventing access to air or oxy-Euthanasia: A method of killing that minimizes pain, gen. distress, and anxiety experienced by the animal Unacceptable: A method that does not meet the re- prior to loss of consciousness, and causes rapid loss quirements of euthanasia. See EUTHANASIA. of consciousness followed by cardiac or respiratory Unconsciousness: Unconsciousness, defined as loss of arrest and death (see sections I3, I5, I6). individual awareness. This occurs when the brain’sExsanguination: The action of draining an animal of ability to integrate information is blocked or dis- blood. rupted. Onset of unconsciousness is associated withFear: An unpleasant emotional experience caused by loss of the righting reflex. An unconscious animal an awareness of a threat of danger. is therefore recumbent and, by definition, unableFeral: A free-roaming, unowned animal of a domestic to perceive pain; however, unconscious animals species that has reverted to wild behavior. may respond to noxious stimulation with spinallyField Conditions: Any situation outside of a con- mediated involuntary movements depending on the trolled or clinical environment. degree of CNS depression present.Finfish: a term used to describe true (vertebrate) fish Wild: A free-roaming animal of a nondomestic species. as opposed to other non-fish aquatic animals such as the invertebrates “starfish” and “cuttlefish”98 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 99. Appendix 1Agents and methods of euthanasia by species. Acceptable With Conditions Methods Acceptable (for Adjunctive Methods, see text) Aquatic invertebrates S6.3: Immersion in anesthetic solution (magnesium S6.3: Adjunctive methods (second step) include 70% salts, clove oil, eugenol, ethanol) alcohol and neutral-buffered 10% formalin, pithing, freezing, boiling Amphibians S7.3: As appropriate by species—Injected S7.3: As appropriate by species—Inhaled anesthetics barbiturates, dissociative agents and anesthetics as as specified, CO2, penetrating captive bolt or firearm, specified, topical buffered tricaine methanesulfonate manually applied blunt force trauma to the head, or benzocaine hydrochloride rapid freezing Avians (See also S5: Intravenous barbiturates S5: Inhaled anesthetics, CO2, CO, N2, Ar, cervical Poultry) dislocation (small birds and poultry), decapitation (small birds) S7.5: Gunshot (free-ranging birds) Cats S1: Intravenous barbiturates, injected anesthetic S1: Barbiturates (alternate routes of administration), overdose, Tributame, T-61 inhaled anesthetic overdose, CO,* CO2,* gunshot* Cattle S3.2: Intravenous barbiturates S3.2: Gunshot, penetrating captive bolt Dogs S1: Intravenous barbiturates, injected anesthetic S1: Barbiturates (alternate routes of administration), overdose, Tributame, T-61 inhaled anesthetic overdose, CO,* CO2,* gunshot* Finfish S6.2: Immersion in buffered benzocaine or benzocaine S6.2: Eugenol, isoeugenol, clove oil, CO2-saturated hydrochloride, isoflurane, sevoflurane, quinaldine water (aquarium-fish facilities/fisheries), sulfate, buffered tricaine methanesulfonate, decapitation/cervical transection/manually applied 2-phenoxyethanol, injected pentobarbital, rapid blunt force trauma followed by pithing, rapid chilling chilling (appropriate zebrafish/research setting) followed by adjunctive method (aquarium-fish facilities), maceration (research setting) Equids S4: Intravenous barbiturates S4: Penetrating captive bolt, gunshot Marine mammals S7.5 (captive): Injected barbiturates S7.7 (free ranging): S7.5 (captive): Inhaled anesthetics Injected barbiturates or anesthetic overdose S7.7 (free ranging): Gunshot, manually applied blunt force trauma, implosive decerebration Nonhuman primates S2.3, S7.4: Injected barbiturates or anesthetic overdose S2.3, S7.4 (as appropriate by species): Inhaled anesthetic, CO, CO2 Poultry S3.4: Injected barbiturates and anesthetic overdose S3.4: CO2, CO, N2, Ar, cervical dislocation (as anatomically appropriate), decapitation, manual blunt force trauma, electrocution, gunshot, captive bolt Rabbits S2.4: Intravenous barbiturates S2.4: Inhaled anesthetic overdose, CO2, cervical dislocation (as anatomically appropriate), penetrating captive bolt Reptiles S7.3: As appropriate by species—Injected S7.3: As appropriate by species—Inhaled anesthetics barbiturates, dissociative agents and anesthetics as as specified, CO2, penetrating captive bolt or firearm, specified manually applied blunt force trauma to the head, rapid freezing for animals < 4 g Rodents S2.2: Injected barbiturates and barbiturate S2.2: Inhaled anesthetics, CO2, CO, tribromoethanol, combinations, dissociative agent combinations ethanol, cervical dislocation, decapitation, focused beam microwave irradiation Small ruminants S3.2: Injected barbiturates S3.2: Gunshot, penetrating captive bolt Swine S3.3: Injected barbiturates S3.3: CO2, CO, N2, Ar, gunshot, electrocution, nonpenetrating captive bolt, manually applied blunt force trauma *Not recommended for routine use.AVMA Guidelines for the Euthanasia of Animals: 2013 Edition 99
  • 100. Appendix 2100 Some acceptable* agents and methods of euthanasia. Ease of Safety for Species Agent Classification Mode of action Rapidity† performance personnel suitability Efficacy and comments Conditions Barbiturates Hypoxia and Depression of the Rapid onset of IV injection is Safe except human Most species, Highly effective when Apply to the use of non-IV routes (see text) cardiac arrest CNS in descending anesthesia necessary for abuse potential; excluding aquatic appropriately administered; attributable to order; loss of best results and DEA-controlled invertebrates when an IV injection would depression of the consciousness requires trained substance be distressful, dangerous, or CNS progressing to personnel; each difficult due to small patient anesthesia, apnea, animal must be size, barbituates may be and cardiac arrest appropriately administered intraperitoneal or restrained intracoelomic (pentobarbitalal combination products have only been approved for IV and intracardiac administration) Benzocaine Hypoxia Depression of CNS Rapid, Easily used Safe Smaller finfish Effective but expensive hydrochloride attributable to and heart depending on and amphibians depression of vital dose centers Carbon dioxide Respiratory Direct depression Moderately Easily with Minimal hazard Most birds Effective, but time required May be used only with those species where acidosis and of cerebral cortex, rapid, depending appropriate with adequate and mammals, may be prolonged in immature aversion or distress can be minimized; gradual produces a subcortical on protocol equipment, closed ventilation excluding and neonatal animals fill method must be used; must be supplied in a reversible structures, and container, gas companion precisely regulated and purified form without anesthetic vital centers; direct source, and once animals contaminants or adulterants, typically from state followed depression of heart protocol are a commercially supplied cylinder or tank; an by hypoxia muscle established appropriate pressure-reducing regulator and attributable to flow meter or equivalent equipment must be depression of vital used centers Carbon monoxide Hypoxemia Combines with Moderate Requires Extremely Most small Effective Acceptable only when equipment is properly hemoglobin and onset time, appropriately hazardous, toxic, species, designed and operated blocks uptake of O2 but insidious maintained explosive in high excluding so that most equipment concentrations, and companion animal species difficult to detect animals are unaware of onset Cervical Hypoxia Direct depression Variable Personnel must be Safe Small birds, Variable Must meet a performance standard of luxation of dislocation of brain and cardiac skilled poultry, mice, the cervical vertebrae without primary crushing fibrillation immature rats (< of the vertebrae and spinal cord—inducing very 200 g), and rabbits rapid unconsciousness Decapitation Hypoxia due to Direct depression Rapid Requires training Guillotine poses Laboratory Irreversible; violent muscle A commercially available guillotine should be disruption of vital of brain and skill potential employee- rodents; small contraction can occur after used if available for the species and application. centers injury hazard rabbits; poultry decapitation In lieu of this, a sharp knife and accurate and birds; and placement are required. some finfish, amphibians, and reptiles Electrocution Hypoxia Direct depression Can be rapid Not easily May be hazardous Used primarily Current must pass through the brain, and cardiac of brain and cardiac performed in to personnel in sheep, swine, fibrillation must never occur before the animal is fibrillation all instances; ruminants, and rendered unconscious; electroimmobilization is requires specialist other animals unacceptable; use of household electrical cords equipment and > 5 kg is unacceptable skilled application Gunshot Physical damage Direct concussion Immediate Requires skill May be dangerous; Large domestic Instant loss of consciousness, Personnel must be trained in the use of firearms; to brain of brain tissue and appropriate aesthetically and selected but motor activity may only in jurisdictions that allow for legal firearm firearm unpleasant for nondomestic continue use; safety of personnel, the public, and other many species animals that are nearby should be consideredAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
  • 101. Appendix 2 (continued) Some acceptable* agents and methods of euthanasia. Ease of Safety for Species Agent Classification Mode of action Rapidity† performance personnel suitability Efficacy and comments Conditions Inhalant Hypoxia Direct depression Moderately Easily performed Effective Most animals Highly effective provided that anesthetics attributable to of cerebral cortex, rapid onset of with closed procedures should excluding subject is sufficiently exposed depression of vital subcortical anesthesia, container be in place to livestock, finfish, centers structures, and vital excitation may (including topical reduce animal and many centers develop during or immersion as worker exposure to amphibians and induction appropriate by anesthetic vapors reptiles species); can be administered to large animals by means of a mask Maceration Physical damage Direct concussion Immediate Easily performed Generally safe; Newly hatched Effective Specialized equipment in excellent working to brain of brain tissue with properly macerated tissues chicks and poults, order must be used designed, may present and pipped eggs commercially biosecurity risks only available equipment and trained personnel Focused beam Brain enzyme Direct inactivation Very rapid Requires training Safe Mice and rats Highly effective for special Only instruments that are designed for this use microwave inactivation of brain enzymes and highly needs and have appropriate power and microwave irradiation by rapid heating of specialized distribution can be used brain equipment Nitrogen, argon Hypoxia Reduces partial Rapid Used in closed Safe if used with Chickens, turkeys, Effective except in young These gases must be supplied in a precisely pressure of oxygen chamber with ventilation and swine and neonates; an effective regulated and purified form withoutAVMA Guidelines for the Euthanasia of Animals: 2013 Edition available to blood rapid filling agent, but other methods are contaminants or adulterants; an appropriate preferable in species where pressure-reducing regulator and flow meter aversion is noted combination or equivalent equipment must be used Potassium chloride Cardiotoxic Direct depression Rapid Requires training Anesthetics may Most species Highly effective, some clonic Intracardially or IV with an animal that is of cerebral cortex, and ability to be hazardous with muscle spasms may be unconscious or under general anesthesia subcortical give IV injection accidental human observed only; unacceptable when used in conscious structures, and vital of potassium exposure vertebrate animals centers secondary chloride to cardiac arrest Penetrating captive Physical damage Direct concussion Immediate Requires skill, Safe Horses, Instant loss of consciousness, Animals be immediately exsanguinated or bolt to brain of brain tissue adequate ruminants, swine but motor activity may pithed unless a powerful captive bolt gun restraint, and and nondomestic continue designed for euthanasia is used; captive bolt proper placement species, as guns used for larger species must have an of captive appropriate extended bolt bolt; can be aesthetically displeasing Tricaine methane Hypoxia Depression of CNS Rapid, Easily used Associated with Finfish, some Effective but expensive The solution should be buffered with sulfonate (TMS, attributable to depending on retinal toxicity in reptiles, sodium bicarbonate; a secondary method of MS 222) decreased nervous dose humans amphibians, and euthanasia is recommended in some finfish and cardiovascular cold-blooded and amphibians function aquatics 2-phenoxyethanol Hypoxia Depression of CNS Rapid, Easily used Safe Finfish There are probably more There are species variations in dosage attributable to depending on efficient immersion agents levels and duration of exposure required depression of vital dose available for euthanasia. Finfish should be kept in centers the 2-phenoxyethanol solution for at least 10 minutes after cessation of opercular movement *Acceptable, acceptable with conditions, and adjunctive methods have been included in this appendix, with the appropriate qualifications. †Immediate = Upon application. Very rapid = Typically within seconds. Rapid = Typically within a few minutes.101 DEA = Drug Enforcement Agency.
  • 102. Appendix 3Some agents and methods that are unacceptable as primary methods of euthanasia. Agent or method Comments Air embolism Air embolism may be accompanied by convulsions, opisthotonos, and vocalization. If used, it should be done only in anesthetized animals. Burning Chemical or thermal burning of an animal is not an acceptable method of euthanasia. Chloral hydrate Unacceptable in dogs, cats, and small mammals. Chloroform Chloroform is a known hepatotoxin and suspected carcinogen and, therefore, is extremely hazardous to personnel. Cyanide Cyanide poses an extreme danger to personnel and the manner of death is aesthetically objectionable. Decompression (excluding low- Decompression is unacceptable for euthanasia because of numerous disadvantages. (1) atmospheric-pressure stunning when Many chambers are designed to produce decompression at a rate 15–60 times as fast as the it can be demonstrated that it achieves recommended optimum for animals, resulting in pain and distress attributable to expanding euthanasia) gases trapped in body cavities. (2) Immature animals are tolerant of hypoxia, and longer periods of decompression are required before respiration ceases. (3) Accidental recompression, with recovery of injured animals, can occur. (4) Bleeding, vomiting, convulsions, urination, and defecation, which are aesthetically unpleasant, may develop in unconscious animals. Diethyl ether Diethyl ether is irritating, flammable, and explosive. Explosions have occurred when animals, euthanatized with ether, were placed in a non-explosion-proof refrigerator or freezer and when bagged animals were placed in an incinerator. Drowning Drowning is not a means of euthanasia and is inhumane. Exsanguination Because of the anxiety associated with extreme hypovolemia, exsanguination as a sole method of killing should be used only on unconscious animals. Formaldehyde Direct immersion of an animal into formalin, as a means of euthanasia, is inhumane with the exception of Porifera. Household products and solvents Acetone, cleaning agents, quaternary compounds (including CCl4), laxatives, pesticides, dimethylketone, quaternary ammonium products, antacids, and other toxicants not specifically designed for therapeutic or euthanasia use are not acceptable. Hypothermia Hypothermia is not an appropriate method of euthanasia. Magnesium sulfate, potassium chloride, Unacceptable for use as euthanasia agents in conscious vertebrate animals. and neuromuscular blocking agents Manually applied blunt force trauma to Generally unacceptable for most species excluding piglets and small laboratory animals. the head Replace, as much as possible, manually applied blunt force trauma to the head with alternate methods. Nonpenetrating captive bolt Unacceptable excluding purpose-built pneumatic nonpenetrating captive bolt guns used on suckling pigs, neonatal ruminants, and turkeys. Neuromuscular blocking agents When used alone, these drugs all cause respiratory arrest before loss of consciousness, so the (nicotine, magnesium sulfate, potassium animal may perceive pain and distress after it is immobilized. chloride, and all curariform agents) Rapid freezing Rapid freezing as a sole means of euthanasia is not considered to be humane with the exception of reptiles and amphibians and < 5-day-old altricial rodents. In all other cases animals should be rendered dead or unconscious prior to freezing. (Rapid chilling of finfish is not considered to be rapid freezing.) Smothering Smothering of chicks or poults in bags or containers is not acceptable. Strychnine Strychnine causes violent convulsions and painful muscle contractions. Thoracic compression Not acceptable for use on a conscious animal.102 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition