AVMA guidelines for the euthanasia of animals 2013 edition

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AVMA guidelines for the euthanasia of animals 2013 edition

  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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

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