Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Compendium of animal reproduction


Published on

MSD Finca Productiva Reproduccion

Published in: Health & Medicine, Technology

Compendium of animal reproduction

  1. 1. Compendium ofAnimal Reproduction
  2. 2. PrefaceIt is with great pleasure that I would like to present to you, colleagues,veterinary practitioners, and students of veterinary medicine and to allothers who share my passion for reproduction science, the newedition of the Intervet Compendium of Animal Reproduction.It has always been my greatest satisfaction to see the sophisticatedscientific discoveries translated into solutions applicable to theeveryday work of a vet for the benefit of the profession and its clients,the animal owners.I would like to express my gratitude and appreciation to Dr. LindaHorspool who reviewed and thoroughly up-dated chapters 7, 8 and 11and to Dr. William Enright who actualised and broadened chapter 12and to Dr. Marc Martens for his valuable contribution to chapter 4.I am also indebted to Dr. David Pepper for his help in correcting andediting the English text.I hope that you the reader will find the Compendium to be a usefulsource of information on this fascinating subject both from the scien-tific and practical point of view.Monika Ptaszynska, editor 9th editionISBN 90-801886-6-2Publisher Intervet International bv060200.04.03.JP9th revised edition, 2006
  3. 3. Table of Contents1 Physiology of Reproduction in mammals 1 1.1 Introduction 1 1.2 Nervous system, hormone system and cell messengers 1 1.3 Regulation of reproduction in the female 5 1.4 Regulation of reproduction in the male 10 1.5 Seasonality 11 1.6 Further reading 122 Bovine Reproduction 13 2.1 Physiology 13 2.2 Herd fertility management 17 2.2.1 Evaluation of fertility 18 2.2.2 Economic aspects 19 2.2.3 Pregnancy diagnosis 20 2.2.4 Oestrus and oestrus detection 23 2.2.5 Timing of insemination 26 2.3 Control of oestrus 27 2.3.1 Reasons for oestrus control 27 2.3.2 Methods of oestrus control 29 2.3.3 Factors affecting fertility of inseminated cows 43 Delayed ovulation 44 Inadequate uterine environment 45 Importance of early luteal function in pregnancy recognition and maintenance 46 Influence of high ambient temperatures on reproductive efficiency in cattle 46 2.3.4 Improvement of conception rate at and after AI 50
  4. 4. Table of Contents 2.4 Reproductive disorders 61 2.4.1 Physiological aspects of the post partum period 62 2.4.2 Retained placenta 64 2.4.3 Uterine infections 65 2.4.4 Anoestrus 73 Treatment of anoestrus in cattle 75 2.4.5 Cystic Ovarian Disease 77 2.4.6 Embryonic mortality 80 2.4.7 The repeat breeder cow 82 2.4.8 Abortion 83 2.4.9 Unwanted pregnancy 92 2.5 Induction of parturition 93 2.6 The bull 94 2.6.1 Evaluation of suitability for breeding 95 2.6.2 Infertility 96 2.7 Embryo Transfer (ET) 97 2.7.1 Management of the donor cow 98 2.7.2 Management of the recipient 100 2.8 Twinning 101 2.9 References 1013 Equine Reproduction 115 3.1 Physiology 115 3.1.1 Physiology of oestrous cycle 115 3.1.2 Fertilisation and pregnancy maintenance 117 3.1.3 Seasonal regulation of reproductive activity in the mare 119
  5. 5. Table of Contents3.2 Reproductive management 1213.2.1 Oestrus detection 1213.2.2 Mating 1223.2.3 Artificial insemination 1223.2.4 Embryo transfer 1243.3 Control of oestrus 1253.3.1 Transition period 1263.3.2 Breeding season 1283.3.3 Induction of ovulation 1293.4 Reproductive disorders 1313.4.1 Retained placenta 1313.4.2 Endometritis/Endometriosis 1323.4.3 Persistent corpus luteum 1363.4.4 Postpartum anoestrus 1363.4.5 Prolonged oestrus 1363.4.6 Embryonic mortality and abortion 1373.4.7 Twin pregnancy and unwanted pregnancy 1393.5 Pregnancy diagnosis 1403.6 Induction of parturition 1413.7 The stallion 1433.7.1 Reproductive performance evaluation 1433.7.2 Cryptorchidism 1453.7.3 Sexual behaviour 1463.7.4 Testicular degeneration 1473.7.5 Haemospermia and urospermia 1473.8 References 148
  6. 6. Table of Contents4 Porcine Reproduction 153 4.1 Physiology 153 4.1.1 The oestrous cycle 153 4.1.2 Domestic versus wild pigs 154 4.2 Reproductive management of sow herds 157 4.2.1 Reproductive parameters 157 4.2.2 Pregnancy diagnosis 159 4.2.3 Oestrus and oestrus detection 159 4.2.4 Timing of mating and artificial insemination 163 4.3 Control of oestrus 165 4.4 Reproductive disorders 169 4.4.1 Anoestrus 170 4.4.2 Repeat breeding 171 4.4.3 Barren sows 172 4.4.4 Abortion 172 4.5 Induction of parturition 173 4.6 The boar 175 4.7 References 1795 Ovine Reproduction 183 5.1 Physiology 183 5.1.1 Seasonality of sexual and ovarian activity 183 5.1.2 The oestrous cycle 185 5.2 Flock reproduction management 186 5.2.1 Introduction 186 5.2.2 Pregnancy diagnosis 188
  7. 7. Table of Contents 5.2.3 Oestrus detection 188 5.2.4 Mating 189 5.2.5 Artificial insemination 190 5.3 Management of oestrus 192 5.3.1 Altering the photoperiod 193 5.3.2 The Ram Effect 193 5.3.3 Progestagen-based methods 194 5.3.4 Prostaglandins 196 5.3.5 Melatonin 197 5.4 Factors affecting oestrus and ovulation 198 5.4.1 Ram effect 198 5.4.2 Genetics 198 5.4.3 Nutrition 199 5.4.4 Gonadotrophins 199 5.4.5 Immunisation techniques 200 5.5 Reproductive disorders 200 5.5.1 Environmental factors and embryo mortality 201 5.5.2 Infectious diseases 201 5.5.3 Nutrition 202 5.6 Induction of parturition 202 5.7 Ram 204 5.8 Embryo technology 205 5.9 References 2056 Caprine Reproduction 207 6.1 Physiology 207 6.1.1 Seasonality of sexual and ovarian activity 207 6.1.2 The oestrous cycle 208 6.1.3 Pregnancy 209
  8. 8. Table of Contents 6.2 Herd reproduction management 209 6.2.1 Introduction 209 6.2.2 Pregnancy diagnosis 211 6.2.3 Oestrus detection and mating 212 6.2.4 Artificial insemination 213 6.3 Control of oestrus 214 6.3.1 Buck effect 214 6.3.2 Progestagen-based methods 215 6.3.3 Prostaglandins 217 6.3.4 Melatonin 218 6.3.5 Photoperiod regimes 218 6.4 Superovulation and embryo transfer 218 6.5 Reproductive disorders 219 6.5.1 Intersexuality (polled gene) 219 6.5.2 Pseudopregnancy 219 6.5.3 Infectious abortion 220 6.5.4 Delayed ovulation/follicular atresia 220 6.6 Induction of parturition 221 6.7 References 2217 Canine Reproduction 223 7.1 Physiology 223 7.1.1 The oestrous cycle of the bitch 223 7.1.2 Hormonal changes in bitches 226 7.1.3 Oestrus induction 227 7.1.4 Prolonged or persistent oestrus 229 7.1.5 Infertility in female dogs 229 Failure to cycle 230 Prolonged primary anoestrus 230 Delayed puberty 230
  9. 9. Table of Contents7.1.6 Short or prolonged interoestrus intervals and split heat 2317.1.7 Prolonged/persistent oestrus 2317.1.8 Failure to conceive/early resorption 2327.2 Mating 2327.2.1 Mating behaviour 2327.2.2 Timing of mating 2337.2.3 Detection of ovulation 2337.3 Pregnancy 2367.3.1 Duration 2367.3.2 Hormonal changes during pregnancy 2367.3.3 Pregnancy diagnosis 2377.4 Parturition 2387.4.1 Initiating events 2387.4.2 Prepartum signs 2397.4.3 Labour 2397.4.3.1 Induction of parturition 2407.4.3.2 Delayed parturition 2407.4.3.3 Retained placentas 2417.5 Unwanted pregnancy (Misalliance) 2417.5.1 Bitches not intended for breeding 2427.5.2 Bitches intended for breeding 2427.6 Oestrus control 2457.6.1 Surgical control of oestrus 2457.6.2 Medical control of oestrus 2467.7 Other conditions of the female urogenital tract 2497.7.1 False pregnancy 2497.7.2 CEH –pyometra complex 2507.7.3 Urinary incontinence 252
  10. 10. Table of Contents 7.8 Male dogs 253 7.8.1 Hypersexuality 253 7.8.2 Cryptorchidism 255 7.9 References 2568 Feline Reproduction 261 8.1 Physiology 261 8.1.1 The oestrous cycle 261 8.1.2 Hormonal changes in tomcats 264 8.2 Mating 265 8.3 Pregnancy 265 8.4 Parturition 266 8.4.1 Normal parturition 266 8.4.2 Dystocia 267 8.5 Mismating and prevention of implantation 267 8.6 Control of reproduction 268 8.6.1 Surgical methods 268 8.6.2 Non-surgical methods 269 Induction of ovulation without copulation 269 Postponement or suppression of oestrus using progestagens 270 8.6.3 Alternatives for the control of reproduction in cats 272 8.7 Disorders of the reproductive tract 274 8.7.1 Queens 274 Cystic endometrial hyperplasia-pyometra complex 274 Failure to cycle 275 Ovarian remnant syndrome 275
  11. 11. Table of Contents Mammary hypertrophy 276 8.7.2 Tom cats 277 Spraying (Inappropriate sexual behaviour) 277 Cryptorchidism or testicular remnants 278 8.8 References 2799 Reproduction in the Buffalo 283 9.1 Introduction 283 9.2 Physiology 283 9.3 Reproduction management 285 9.4 Reproductive disorders 288 9.4.1 Uterine disorders 288 9.4.2 Ovarian disorders 288 9.5 References 29010 Reproduction Camelidae 293 10.1 Physiology 293 10.1.1 Seasonality 294 10.1.2 The oestrous cycle 294 10.1.3 Pregnancy and parturition 296 10.2 Management of reproduction 296 10.2.1 Reproductive parameters 297 10.2.2 Mating and artificial insemination 298 10.2.3 Pregnancy diagnosis 299
  12. 12. Table of Contents 10.3 Control of oestrus 300 10.3.1 Induction of oestrus 300 10.3.2 Induction of ovulation 300 10.3.3 Superovulation 301 10.4 Reproductive disorders 301 10.5 References 30311 Reproduction in the Rabbit 305 11.1 Physiology 305 11.1.1 Buck 305 11.1.2 Doe 305 11.2 Management of reproduction in commercial rabbits 308 11.2.1 Natural mating 309 11.2.2 Artificial insemination 309 11.2.3 Pregnancy diagnosis 311 11.3 Control of reproduction 312 11.3.1 Induction of receptivity 312 11.3.2 Induction of ovulation 313 11.4 Induction of parturition 314 11.5 Reproduction in pet rabbits 315 11.5.1 Bucks 315 11.5.2 Female pet rabbits 315 11.6 References 316
  13. 13. Table of Contents12 Fish Reproduction 319 12.1 Introduction 319 12.2 Physiology and conditioning 319 12.3 Reproductive management by using hormone preparations 325 12.4 Induction of spawning 327 12.5 Mode of administration 329 12.6 Propagation 331 12.7 Reproduction-related diseases 332 12.8 Gender control 333 12.9 Transgenesis 334 12.10 Aknowledgements 335 12.11 References 33513 Product Information 341 13.1 Introduction 341 13.2 Chorulon® 341 13.3 Chorulon® in fish breeding 343 13.4 Chrono-gest CR® 345 13.5 Covinan® (Delvosteron®) 346 13.6 Crestar® 349
  14. 14. Table of Contents13.7 Cyclix Bovine® 35113.8 Cyclix Porcine® 35213.9 Cyclix® 35413.10 Dexadreson® 35613.11 Dexafort® 35813.12 Dexamedium® 36013.13 Durateston® 36113.14 Fertagyl® 36313.15 Folligon® (Chrono®-gest PMSG) 36513.16 Incurin® 36713.17 Intertocine®-S (Oxytocin-S) 36813.18 Mesalin® 37013.19 Metricure® 37113.20 PG 600® (Suigonan) 37213.21 Preloban® 37413.22 Prosolvin® 37513.23 Receptal® 37913.24 Regumate Equine® 38113.25 Regumate Porcine® 382
  15. 15. Physiology of Reproduction in Mammals 11. Physiology of Reproduction in Mammals1.1 Introduction Two regulatory systems govern the reproductive process in mammals. The endocrine system and the nervous system each has a specific role, and a subtle interplay between the two is essential for the cascade of events that results in the birth and successful rearing of healthy offspring. This first chapter will provide some basic theory about the way in which the reproductive processes function, using a brief glimpse of what happens in the cow to illustrate the relation- ships between the different parts of the process. More detailed information about the reproductive cycle in cattle and other ani- mals can be found in the chapters on the various species. Short sections at the end of this chapter discuss the endocrine process in the male, and some aspects of seasonality.1.2 Nervous system, hormone system and cell messengers Nervous system: Stimuli from the environment are received by the senses and transmitted to the brain. With respect to repro- duction, examples of sensory input from the environment in- clude information received via the eyes (light, other animals of the same species), the nose (sexually significant odours), and touch (proximity of other animals), and the optic, olfactory and sensory nerves transmit the messages to the brain. The brain translates the information and, as necessary, reacts by sending impulses along nerve fibres to a target organ. Hormone system: A hormone can be defined as a chemical sub- stance, produced in a gland or tissue in the body, which evokes a specific reaction in hormone-sensitive tissue. The hormone system exerts its influence by means of these chemical mes- sengers. It is regulated by a complex of feedback loops, and impulses from the nervous system and various organs. Its activ- ity can be subdivided according to the way the hormones reach the target cells (Norman and Litwack 1997). 1
  16. 16. 1 Physiology of Reproduction in Mammals Systemic hormones-endocrine hormones In the endocrine system, the hormone is synthesized and stored in specialized cells of an anatomically defined endocrine gland. These hormones are released into the blood stream and carried (frequently by specific transport proteins) to a target organ, of- ten distant from the source. The endocrine system includes secretory glands that release their hormones into the general circulation (e.g. insulin), as well as into closed circulatory systems (e.g. GnRH). Paracrine hormones So-called paracrine hormones influence cells or organs in their immediate neighbourhood. For example, the production of tes- tosterone by the interstitial Leydig cells of the testes, acting on the adjacent seminiferous tubules. Autocrine hormones Autocrine describes the process in which the producing cell is also the target cell. The prostaglandins are good examples. Neurotransmitters Nowadays, neurotransmitters are increasingly commonly con- sidered to be hormones, i.e. they are hormone messengers. Neurotransmitters such as acetylocholine may be thought of as paracrine hormones. To date, more is known about endocrine functions than about the rest of the hormone system. In the last decade, research workers have paid more attention to the paracrine and auto- crine functions, but many details of these actions are still poorly understood. Having reached a target cell the hormone needs to provoke a reaction, which is activated by the target cell’s hormone-specific receptors - unique molecular structures, in or on the cell, with a highly specific affinity for a particular hormonal configuration. The receptors therefore perform two important functions: • Recognition of the specific hormone by the target cell. • Translation of the signal into a cell-specific response.2
  17. 17. Physiology of Reproduction in Mammals 1The biochemical structure of hormone receptors can vary but,in general, each can recognise and interact with, a very specifichormone entity (by contrast with the lock-and-key model of thesubstrate-enzyme interaction).Nonetheless all receptors have two key components:a) a ligand binding domain that binds the matching hormone stereo-specificallyb) an effector domain that recognises the presence of the li- gand domain-hormone complex and activates the cell-spe- cific biological response, which usually involves activation or de-activation of enzymes in the target cells.The receptors for steroid hormones are usually to be foundin the cytosolic and nuclear compartments of the target cellswhere they interact directly with DNA. Receptors for peptide andprotein hormones are usually located in the outer membrane ofthe cell. Most receptors, especially those in the cell membrane,require a second messenger to transmit the message. One ofthe best known second messengers is cyclic–AMP, as shown inFigure 1. After binding to the receptor, the hormone activatesthe adenylate-cyclase-system in the cell membrane. ATP is thenconverted into cyclic AMP. cAMP, the second messenger, in itsturn, activates an inactive cAMP-protein-kinase-A that splits upinto an active catalytic unit and a regulatory unit. The activecatalytic unit of the protein-kinase stimulates the phosphoryla-tion of a protein or enzyme, which then brings about the cellulareffects, such as protein synthesis, growth or hormone secretion.Because of the generally low circulating concentrations of hor-mones, the receptor needs a very efficient capture mechanismfor its matching hormone. 3
  18. 18. 1 Physiology of Reproduction in MammalsFigure 1 Cyclic AMP as second messenger. The effect of an endocrine hormone release can vary with par- ticular circumstances. The number and type of receptors of a target cell are not fixed, and their formation and degradation is a dynamic process. The function of one hormone in a cell can be the induction or degradation of receptors for another mes- senger. Furthermore, receptors can be blocked by an excess of hormones. In this case, over-stimulation by a normally highly effective dose of hormones will cause no further effect. Many pathological conditions in the reproductive process are caused by disorders at the receptor level.4
  19. 19. Physiology of Reproduction in Mammals 11.3 Regulation of reproduction in the female For most of a normally fertile female’s life, she experiences no regular cyclic activity (anoestrus). Taken together, the periods of inactivity in pre-puberty, pregnancy and lactation are much lon- ger than the relatively short periods of cyclic activity. Neverthe- less, most attention is focused on the latter, the periods when man most frequently interferes with the reproduction process (breeding/not breeding; choice of male/AI; control of oestrus; induction of ovulation etc.) and it is during these periods that most problems associated with breeding occur. The principles of the hormonal control of reproduction are basi- cally the same for all the domesticated animal species, though there are some differences between them. Some animals are poly-oestrus (cattle, swine) cycling throughout the year, others are only seasonally poly-oestrus (horse, sheep, cat). The dog is mono-oestrus. There are also differences in the mechanism of ovulation. Most animals are spontaneous ovulators, but in the cat, rabbit and camel, ovulation is induced by the stimulation of sensory re- ceptors in the vagina and cervix at coitus. The species-specif- ic aspects of reproduction are covered in the chapters on the physiology of the different species. This section will only review the function and interaction of the most important hormones involved in reproduction (and their secretory and target tissues), using the sexual cycle of the cow as an example. The reproductive process in mammals is regulated by a com- plex, and only partially understood, cascade of the combined activities of the central nervous system, a number of secre- tory tissues, target tissues and several hormones. Figure 2 is a schematic representation of the most important organs and hormones involved in reproduction in the female, with some of their functions and interactions. 5
  20. 20. 1 Physiology of Reproduction in MammalsFigure 2 Inter-relationships in the control of female reproductive function. The central nervous system (CNS) receives information from the animal’s environment (visual, olfactory, auditory, and tactile stimuli) and conveys the information relevant for reproduction to the gonads via the Hypothalamo-Pituitary-Gonadal axis. The hypothalamus and the pituitary gland are closely attached to the ventral part of the brain. Both are not only hormone producers, but also target organs, constituting a sophisticated homeostatic feedback system by which they regulate their own rate of secre- tion. Following a stimulus from the CNS, endocrine neurons in the hypothalamus produce one of its releasing hormones, Gonado- trophin Releasing Hormone (GnRH). GnRH is transported via the6
  21. 21. Physiology of Reproduction in Mammals 1hypothalamo-hypophyseal portal system to the anterior lobe ofthe pituitary gland, its target organ. Here it stimulates specificcells of the pituitary gland to secrete Follicle Stimulating Hor-mone (FSH) and Luteinizing Hormone (LH). GnRH, FSH and LHare not released at a constant level, but in a series of pulses.FSH stimulates the development of ovarian follicles. In the thecainterna of the follicle, LH stimulates the synthesis of androstene-dione from cholesterol.Androstenedione is converted into testosterone which is aro-matized into oestradiol-17β under the influence of FSH, in thegranulosa cells of the follicle. Oestradiol exerts a positive feed-back on the hypothalamus and pituitary gland, increasing thefrequency of the GnRH pulses. Above a certain threshold levelof oestradiol, the hypothalamus responds with a surge of GnRHwhich, in turn, induces an LH surge that initiates ovulation.Thus, with respect to ovarian function, FSH stimulates thegrowth of follicles, while LH stimulates their maturation, oestra-diol production and ovulation. LH also supports the formationand the early function of the corpus luteum.One of the principal effects of oestradiol is the induction of thesigns of oestrus. Oestrus can be described as the behaviouraland physical signs that signal to other animals that the femaleis in the fertile phase of her cycle, and will allow herself to bemated.The granulosa cells also produce inhibin. Not all the effects ofthis hormone are understood, but its name is derived from itsnegative feedback on FSH release from the pituitary gland, thuscontrolling follicle development. After ovulation, the remnants ofthe follicle are remodelled into the corpus luteum, under the in-fluence of LH. The cavity of the follicle is filled with blood vessels,and the granulosa cells increase in size. The corpus luteum ismainly a secretory organ producing progesterone and oxytocin.Progesterone is essential for the normal cycle in the cow and, af-ter conception, it is the hormone principally responsible for themaintenance of pregnancy. It reduces the GnRH pulse release, 7
  22. 22. 1 Physiology of Reproduction in Mammals and therefore inhibits new ovulations. Furthermore, it prepares the endometrium for the nidation (in effect, the implantation) of the developing embryo, and inhibits uncontrolled contractions of the uterine wall which would be harmful to pregnancy. If the ovum released from the follicle during ovulation is not fertil- ized, no signal of pregnancy will be received from the embryo. At around day 16 after ovulation, the endometrium of the non- pregnant uterus will release prostaglandin F2α. PGF2α initiates the regression of the corpus luteum which is called luteolysis. The luteolytic mechanism of prostaglandins has not been completely elucidated, but it involves a reduction of the blood supply to the corpus luteum by vasoconstriction, as well as a direct effect on the luteal cells themselves. Oxytocin produced in the corpus luteum is also thought to play a part in luteolysis. As a result of the regression of the corpus luteum, blood pro- gesterone concentrations decline, removing the blocking effect on GnRH release from the hypothalamus. This initiates a new follicular phase and the final development of a pre-ovulatory fol- licle. The period of follicle ripening, oestrus and ovulation, char- acterized by the production of oestradiol, is called the follicular phase of the cycle. The progesterone-dominated phase, from ovulation to luteolysis, is called the luteal phase. See Figure 3.Figure 3 Hormone levels during the oestrous cycle of a cow.8
  23. 23. Physiology of Reproduction in Mammals 1 The hormones involved in reproduction are listed in Table 1, along with the main function, origin and chemical structure of each. It is important to note that only some of the known actions of the individual hormones are included, and also that not all the functions of these hormones are understood. The table merely includes the known endocrine actions, but most also have vari- ous paracrine functions, which have not yet been sufficiently explored. Reproduction in the female and the male is regulated by the finely tuned interplay of actions and reactions of many of these hormones. Although much progress has been made in recent decades, a total understanding of these immensely com- plex processes is still to be attained.Table 1 Hormones involved in reproduction, their origin, main function and chemical structure α 9
  24. 24. 1 Physiology of Reproduction in Mammals1.4 Regulation of reproduction in the male The principles of reproduction in the male show a pattern simi- lar to those of the female. The hormones responsible for the development and mainte- nance of the male phenotype are also the gonadotrophins: luteinizing hormone (LH, which in the male used to be called interstitial cell stimulating hormone ICSH) and follicle stimulat- ing hormone (FSH) produced by pituitary gland; the androgenic steroid hormones, including testosterone, produced by the tes- tes, and inhibin. The female steroid hormones, oestradiol and oestrone, also play an important part in the male in certain cir- cumstances. Figure 4 represents the control of reproductive function in the male. GnRH from the hypothalamus stimulates the release of FSH and LH. FSH acts directly on the seminiferous tubules of the testis (germ cells and Sertoli cells), stimulating spermatogenesis. The Sertoli cells produce inhibin, which has a negative feedback effect on FSH secretion by the pituitary gland. LH stimulates the production of testosterone by the Leydig cells. Testosterone (acting on the Sertoli cells) is also necessary for spermatogenesis. It and other androgens are responsible for the differentiation and maturation of the male reproductive organs, the development of the male secondary characteristics, and the behaviour consistent with the male’s role in reproduction. Tes- tosterone exerts a negative feedback effect on LH secretion by suppressing the pulsatile GnRH release from the hypothalamus.10
  25. 25. Physiology of Reproduction in Mammals 1Figure 4 Inter-relationships in the control of male reproductive function.1.5 Seasonality In temperate latitudes, animals are faced with recurrent, season- al changes in temperature, climate and food availability, which can influence their reproductive activity. One of the common features of most wild, and some domesticated, species is the development of seasonal reproduction favouring birth at an op- timal time of year, usually spring, which allows the new-born to grow under optimal conditions of climate and food availability before the following winter. This means that periods of sexual activity (the oestrus season) al- ternate with periods of sexual inactivity (the anoestrus season). Among the domesticated species, sheep, goats and horses have retained the strongest seasonality in their reproductive processes. In sheep, for instance, sexual activity begins as the day length becomes shorter (short-day breeders), and in horses, sexual activity starts when day length increases (long-day breed- ers). In temperate and cold climates, this results in horses and sheep giving birth to their young in spring, when sufficient food is likely to give them the best chance of survival. 11
  26. 26. 1 Physiology of Reproduction in Mammals The pineal gland is the main regulatory organ in the seasonality of breeding; it registers day length via the eyes and a complex of neural connections, see Figure 5. The pineal gland produces indoleamins, of which melatonin is the most important. Melatonin is produced and secreted during the night (dark). As days become shorter, the animal’s exposure to melatonin increases. By some means not yet fully elucidated, this exerts a stimulating effect on GnRH secretion by the hy- pothalamus in short-day breeders such as sheep. In long-day breeders, such as the horse, increased melatonin exposure has the opposite effect, inhibiting GnRH release by the hypothala- mus. Thus differences in day length are recognised and trans- lated into signals able to turn sexual activity on or off .Figure 5 Role of the pineal gland and melatonin in reproduction.1.6 Further reading Norman AW and Litwack G. Hormones. 2nd Edn. Academic Press, 1997. Thiéry JC., Chemineau P., Hernandez X., Migaud M., Malpaux B. Neuro- endocrine interactions and seasonality. Dom Anim End 2002;23: 87–100 Mihm M., Bleach ECL. Endocrine regulation of ovarian antral follicle de- velopment in cattle. Anim Reprod Sci 2003;78:217–237 Ginther OJ., Beg MA., Donadeu FX., Bergfelt DR. Mechanism of follicle deviation in monovular farm species. Anim Reprod Sci 2003;78:239–25712
  27. 27. Bovine Reproduction 22 Bovine Reproduction2.1 Physiology Nutritional influence Numerous studies in dairy herds have clearly shown that a marked increase in milk production during early lactation in- creases the incidence of various reproductive problems (Grohn et al, 1994; Macmillan et al., 1996; Poso et al., 1996). Further- more, the genetic capacity for extremely high levels of milk pro- duction in dairy cattle, together with changes in their nutritional management and larger herd sizes, have been associated with a gradual decline in fertility. The inability to meet the high en- ergy requirements for both maintenance and production in high- yielding cows leads to a negative energy balance, particularly during the first few weeks after calving. Energy balance during the first three weeks of lactation is highly correlated with the interval between calving and first ovulation (Butler et al., 2000). It has been well documented that cows in too fat a condition at calving often have a reduced appetite and eventually develop a greater negative energy balance than that of their normal herd mates. These cows exhibit a more extensive mobilisation of body fat and and a greater accumulation of triacylglycerols in the liver (Rukkwamsuk et al., 1998) leading to hepatic lipidosis which is associated, by many authors, with impaired fertility in the post partum period. Moreover, it has been reported that severe negative energy bal- ance may prolong the interval between calving and first ovula- tion. Low energy availability during the first few weeks of lacta- tion impairs LH secretion, but it also reduces the responsiveness of the ovary to LH stimulation (Jolly et al., 1995; Butler 2000). Endocrine environment in high-yielding dairy cows Most available large data sets demonstrate an antagonistic rela- tionship between milk production and fertility. Nonetheless the extent of this effect has been questioned, especially, as with many of the reproductive indices, no clear relationship with milk production has been established so far. However, observations 13
  28. 28. 2 Bovine Reproduction in the field clearly indicate that high yielding dairy cows have much lower conception rates than heifers. The possible nega- tive effect of high levels of milk production on the reproductive performance of high-yielders can be modulated through various aspects of reproductive function. There is no uniform confirmation, in the literature, of a negative effect of high milk production levels on the intensity and dura- tion of heat. However, both veterinary practitioners and farm- ers alike report that high-yielding dairy cows pose a problem with respect to oestrus detection. In a trial reported by Lopez et al. (2004) the duration of oestrus was correlated positively with peak oestradiol concentrations, and correlated negatively with milk production. Wiltbank et al. (2006) suggested that high levels of milk production lead to reduced circulating oestradiol concentrations, resulting in the decreased duration and inten- sity of oestrus. Decreased oestradiol concentrations could also cause increased follicular size because of the extended interval before the oestradiol-induced oestrus, GnRH-LH surge and ovu- lation of high yielding cows. It now seems clear that very high-yielding cows may exhibit a different endocrine status to non-lactating cows, due to their high metabolic rate. Cows producing more milk develop larger follicles, but with lower circulating oestradiol concentrations (Lopes et al., 2004). Moreover, these high level producers have a greater volume of luteal tissue, but reduced circulating proges- terone concentrations. The most likely explanation is that the metabolism of steroid hormones increases as milk production increases in lactating dairy cows. Wiltbank et al. (2006) proposed that some of the reproductive changes in lactating dairy cows are caused by a dramatic in- crease in steroid metabolism due to the enhanced feed intake and blood flow through the liver. In lactating dairy cows, a con- tinuously high plane of nutrition leads to chronically elevated hepatic blood flow, and approximately double the rate of me- tabolism of steroid hormones observed in their non-lactating peers of similar size and age. Results of recent trials indicate that, even with a similar level of hormone production, the level of circulating concentrations of steroid hormones is lower dur- ing lactation (Sangsritavong et al., 2002; Wiltbank et al., 2006).14
  29. 29. Bovine Reproduction 2In addition to lower oestradiol concentrations at the start of oes-trus, there is also likely to be a more rapid reduction in circulat-ing oestradiol after LH surge due to the increased metabolismof this steroid. This would result in a shorter duration of oestrusin high-yielding cows. Elevated steroid metabolism due to highmilk production levels can also have a more profound detrimen-tal effect on fertility. The pre-ovulatory follicle and oocyte maybe exposed to an extended period of elevated LH pulses, whichin turn may lead to ovulation of an over-stimulated or prema-turely-activated oocyte and thus to reduced fertility. Also thereduced rate of rise of progesterone following ovulation can re-duce fertility because of the poorer survival of embryos.Physiology of the oestrous cycle in cattleThe sexual cycle of the cow is generally independent of the sea-son of the year. Oestrus or ‘heat’ is observed every 21 days onaverage, with a range of 18-24 days. Oestrus is taken as dayzero of the cycle. It is of relatively short duration, lasting onaverage 18 hours, with a range of 4-24 hours. Ovulation takesplace about 30 hours after the onset of oestrus, that is, after theend of behavioural oestrus. Fertilization of the ovum takes placein the oviduct. The blastocyst arrives in the uterus at around day5. Pregnancy lasts for 279-290 days. The interval from calvingto first ovulation varies greatly depending on the breed of cow,nutrition, milk yield, season and the presence of a sucking calf.The first ovulation after calving is frequently not accompaniedby oestrus behaviour, and is known as a ‘silent heat’. See also2.4.1.Follicular growth in cattleFollicular growth and development in ruminants is characterizedby two or three consecutive follicular waves per oestrous cycle.The coming of ultrasonography has allowed much informationto be gathered about the stages of follicular growth and selec-tion. Each wave involves the recruitment of a cohort of folliclesfrom the total ovarian follicular stock, and the selection of adominant follicle which continues to grow and mature to thepre-ovulatory stage while the others undergo atresia.Three distinct stages can be distinguished in follicular develop-ment: growth, selection and deviation phases.Each wave consists of the simultaneous recruitment of three to 15
  30. 30. 2 Bovine Reproduction six follicles to grow larger than 4–5 mm in diameter. Within a few days of the start of a wave, one follicle emerges as domi- nant. The dominant follicle continues to grow and differentiate, whereas its sister follicles stop growing, and regress. The domi- nant follicle of the first wave in two-wave cycles, and of the first and second waves in three-wave cycles, regresses. However, the dominant follicle of any follicular wave, including the first, can ovulate if the appropriate endocrine conditions are provided by the induction of luteolysis (by the injection of prostaglandin F2α) during its tenure of dominance. The recruitment of waves of follicles In cattle and other species, follicular waves are preceded or ac- companied by a small rise in FSH. All follicles growing as a cohort contain specific receptors for FSH and depend on this gonadotrophin for their growth. At this stage the growing follicles do not have a sufficient population of LH receptors to respond to an LH-like stimulation, which is why this stage of growth is sometimes called FSH-dependent. In cattle, sequential FSH rises, associated with new waves of fol- licles, occur during the oestrous cycle, in the post partum pe- riod, during pregnancy and before puberty. Selection of the dominant follicle For reasons not yet properly understood, only one dominant fol- licle is selected from the cohort recruited by the small rise in FSH. A defining characteristic of the dominant follicle appears to be its greater capacity for oestradiol production. Secretion of oestradiol, and perhaps androgen, by the dominant follicle is associated with the cessation of the rise in FSH, and then its maintenance at basal levels (Ginther et al., 2000 a,b). The fu- ture dominant follicle acquires LH receptors which allow it to continue to grow in the environment of low FSH and increasing LH levels. By indirectly lowering the FSH level, the dominant follicle de- creases the support crucial for the subordinate follicles by re- ducing the component vital for their growth, while at the same time benefiting from both the low FSH and increasing LH levels. Recently, important information has emerged about the role of other modulators such as growth factors, inhibin and insulin in the differentiation and selection of the dominant follicle (For- tune et al., 2001; Mihm et al., 2003).16
  31. 31. Bovine Reproduction 2 Selected dominant follicle Following its selection, the growth, oestrogen activity and lifespan of the dominant follicle are controlled by the LH pulse pattern. Therefore any changes in the GnRH, and thus the LH, release pattern will have a profound effect on the continued growth of the dominant follicle and its ovulation. It is now well known that the increased frequency of LH pulses seen following progestagen treatments, for example, will prolong the period of dominance of this follicle from 2-7 days to more than 14 days, which affects the fertility of the oocyte (Diskin et al., 2002). Nu- tritional, environmental and even infectious factors, which di- rectly and indirectly affect the GnRH/LH pattern in cattle, will have a considerable effect on the fate of the dominant follicle, and consequently on ovulation and fertility. Follicular Dynamics in a 3-wave cycle2.2 Herd fertility management For the optimal production of both milk and calves, the target is generally for every cow in the herd to produce a live healthy calf each year, i.e. to have a calving interval of 365 days. The control of reproduction in the dairy herd is only one compo- nent of the whole farm management package, which should be the preserve of the veterinary practice. Communicating, to the farmer, the value of the cost-benefit of veterinary services is a key feature for the success of herd health programmes. This chapter deals with the main aspects of herd fertility man- agement. 17
  32. 32. 2 Bovine Reproduction2.2.1 Evaluation of fertility Table 1 lists the parameters and targets commonly used to analyse and evaluate fertility in the dairy herd.Table 1 Reproduction parameters and targets for dairy herds. Parameter Target Calving-conception interval < 90 days (av. number of days open) Calving-1st insemination interval < 70 days Conception rate at 1st insemination > 60% Number of inseminations per conception < 1.5 Abortions < 3% (between 45-265 days of pregnancy) Culling due to infertility < 5% Age at first calving 24 months In the beef suckler herd, the weaned calf is the main source of income. The key figures for reproductive performance are shown in Table 2.Table 2 Reproduction parameters and targets for beef herds. Parameter Target Length of the breeding period < 63 days Pregnancy rate > 95 % (35 days after the end of the breeding season) Percentage calves born alive > 93 % (of cows confirmed pregnant) Note that these figures apply to intensively managed dairy and beef herds in temperate climates. Comparisons should only be made between herds kept in the same or similar regions.18
  33. 33. Bovine Reproduction 22.2.2 Economic aspects There are three main components of economic loss due to fertil- ity problems: - losses due to incorrectly timed or ineffective AI - extended calving intervals - culling for reasons of reproductive failure of animals with high genetic potential Losses due to incorrectly timed AI Endocrine disorders affecting reproductive performance in cattle often manifest themselves in the irregularity of the oestrous cy- cle, inadequate signs of heat or delayed ovulation. The result is likely to be the incorrect timing of artificial insemination, which can also be due to poor management. Repeat inseminations in- crease the costs of service and are wasteful of semen. Extended calving interval Longer calving intervals result in a longer lactation and a longer dry period. The total loss increases with the length of the calving interval (see Table 3). Extended calving interval is a direct result of increased calving to conception interval and is expressed in the number of so-called ‘days open’. It has been a commonly recognised fact that an in- creased calving to conception interval results in losses which can be expressed in reduced overall milk production (see Table.3).Table 3 Estimated losses associated with days open in dairy herds Source: Esslemont and Kossaibati, 2002 Lactation Loss nett per day in milk litres Medium milk yield – 6.000 L/lactation (305d) 1 10.88 L 5 15.03 L Average 13.72 L High milk yield of 10.000 L/lactation (305d) 1 16.97 L 5 21.18 L Average 19.87 L 19
  34. 34. 2 Bovine Reproduction Culling for reasons of reproductive failure The losses caused by premature culling due to infertility depend on the age and the production level of the cow culled. These losses represent the missed future income from that cow. They are maximal for a high-yielding cow in her second lactation, and thereafter decrease with age and lower production level (Dijkhuizen et al., 1991) When a valuable young cow is culled, it is not only her future milk production which is lost, but also her genetic potential as the source of replacement heifers.Figure 1 Estimated cost of culling in the herd Adapted from Source: Esslemont and Kossaibati 20022.2.3 Pregnancy diagnosis Accurate and early diagnosis of pregnancy in both dairy and beef herds is essential for the maintenance of high levels of re- productive efficiency. It is required for the early identification of fertility problems at both individual animal and herd level. Non-return to oestrus If a cow is not observed in oestrus at around 3 weeks after ser- vice or insemination, she is generally assumed to be in calf. However, even if oestrus detection is good, not all of these cows will be pregnant. On the other hand, up to 7% of pregnant cows will show some signs of oestrus during pregnancy. Insemination of these animals may result in embryonic or foetal death.20
  35. 35. Bovine Reproduction 2 Rectal palpation The advantage of rectal palpation is that it gives an immediate answer and, in the absence of pregnancy, the cow can receive early treatment. Early pregnancy diagnosis (1-3 months) is based on a combina- tion of the following: asymmetry of the uterine horns, lesser tone of the pregnant horn and fluctuant contents in the preg- nant horn (later both horns), a palpable corpus luteum on the ovary on the same side as the pregnant horn, membrane slip and appreciation of an amniotic vesicle. In the later stages of pregnancy (>3 months), the cervix is located anterior to the pel- vic rim and the uterus cannot be easily retracted. The uterus is flaccid and placentomes, and sometimes the foetus, are palpa- ble. The median uterine artery increases in diameter and fremi- tus can be detected. See Table 4.Table 4 Positive signs of pregnancy at rectal palpation Common reasons for errors in rectal palpation include failure to retract the uterus, abnormal uterine contents (pyometra or mucometra) and incorrect service dates. (Early or inappropriate palpation of the amniotic vesicle may damage the embryo and cause embryonic mortality.) Progesterone assay The progesterone secreted by a functional corpus luteum be- tween 18 and 24 days after service or insemination is an early 21
  36. 36. 2 Bovine Reproduction indication of pregnancy. It can be assayed in milk or plasma. The optimum time for the assay is 24 days after service or AI, eliminating the problem of long oestrus intervals which might lead to a false positive diagnosis. The sensitivity (i.e. accuracy in detecting pregnancy) of the cow- side milk progesterone (EIA) test was 93.1% in a study by Piet- erse et al. (1989). However, its specificity (i.e. accuracy in detect- ing non-pregnancy) was only 39.3%, which meant that there was a rather large number of animals diagnosed as pregnant, which were in fact not pregnant. The most common reasons for error are pyometra/persistent cor- pus luteum, short oestrus intervals, cystic ovarian disease (luteal cysts) and the incorrect handling of the samples and test kit. Ultrasound examination The use of transrectal ultrasonography to assess pregnancy sta- tus early in gestation is among the most practical applications of ultrasound for dairy cattle reproduction. Early identification of non-pregnant cows following natural or artificial insemination improves reproductive efficiency and pregnancy rate by reduc- ing the interval between AI services and increasing AI service rate. Real time (B-mode) ultrasound is a reliable and relatively simple method of diagnosing pregnancy as early as day 26. Using ultrasound scanning techniques, an accuracy of over 99% can be achieved, enabling fertility problems to be identified rapidly. Generally, two factors affect the speed at which ultra- sound examinations can be conducted on a dairy farm: operator proficiency and the availability and restraint of animals. When both factors are optimized, the speed of ultrasonography can approach that of rectal palpation, while exceeding the latter in the amount of information gathered from each animal. The main advantage of scanning is that it can give an accurate diagnosis earlier than rectal palpation.22
  37. 37. Bovine Reproduction 2Table 5 Day of first detection of ultrasonographically identifiable characteristics of the bovine conceptus. First day detected Adapted from Curran et al., 1986. Because pregnancy can be identified earlier using ultrasound than by rectal palpation, the rate of pregnancy loss detected is often higher. Of cows diagnosed pregnant at 28 days after AI, 10 to 16% experience early embryonic loss by 56 days (Mee et al., 1994; Vasconcelos et al., 1997). Therefore, cows diagnosed pregnant at 28 days after AI, using ultrasound, should be sub- mitted to a subsequent examination at around 60 days, after which the rate of embryonic loss will be much less (Vasconcelos et al., 1997).2.2.4 Oestrus and oestrus detection Reproductive performance is a major factor affecting the pro- duction and economic efficiency of dairy and beef herds. For herds using artificial insemination, heat detection rate and calv- ing rate are two major determinants of the compactness of the calving season and ultimately of the calving-to-calving interval. Insufficient and/or inaccurate oestrus detection leads to delayed insemination, reduced conception rates and thus extended calv- ing intervals. 23
  38. 38. 2 Bovine Reproduction Oestrus Oestrus is the complex of physiological and behavioural signs occurring just before ovulation. The length of oestrus varies from 4 to 24 hours. The signs of oestrus are: standing when mounted; swollen vulva; hyperaemic vaginal mucosa; clear and elastic mucous vaginal discharge; ruffled tailhead, possibly with minor skin lesions; restlessness; group formation; chin rubbing; flehmen; licking, pushing, fighting, mounting other animals; lor- dosis; and possibly reduced feed intake and/or milk yield. Oestrus signs, especially when several animals are in (pro-) oes- trus simultaneously, are often misinterpreted. Of all the signs the standing reflex (standing when mounted) is a truly reliable indication of oestrus. The cow is then said to be in ‘standing heat’.Table 6 Accuracy of visual heat detection in relation to the number of observations per day: Heat detection aids There are several aids to facilitate oestrus detection. Heat mount detectors Heat mount detectors are glued on the mid-line of the back of the cow, just in front of the tail-head. A ‘triggered’ detector in- dicates that the animal has been mounted. Experimental evalu- ation has produced conflicting results. Loss of the detector, poor performance in cold weather and a high proportion of false positives when animals are housed close together, have all been reported to account for this. Recent technological advances have allowed heat-mount detec- tion devices to become more sophisticated. Some detectors now flash to indicate how many times the cow has been mounted and how much time has elapsed since it was first mounted.24
  39. 39. Bovine Reproduction 2However, perhaps the most sophisticated detector comprises apressure sensitive battery-operated radio transmitter. When ac-tivated, the transmitter emits a radio-signal which is picked upby a receiver. The signal is then digitalised and stored on com-puter together with the date and time, duration of each mountand the cow’s identity. This has been widely used in the US.Tail paint, a strip of brightly-coloured paint (20 cm long and 5cm wide) lightly applied to the midline area in front of the tailhead which will be rubbed by mounting cows, should last forat least 4 weeks unless rubbed. It appears to improve the ef-ficiency of oestrus detection, though cubicle housing and highcattle density increase the number of false positives.TeasersTeaser animals, i.e. vasectomised bulls or testosterone-treatedcull cows, will mount a cow in heat and thus attract the attentionof the herdsman. They may be equipped with a chin ball markeror a raddle. Aggressive behaviour, and the development of fa-vouritism (ignoring cows in heat other than favourites), are dis-advantages of this system. Moreover, vasectomised bulls maybe vectors of venereal diseases.PedometersCattle in heat walk at least twice as much as they do beforeand after heat. Thus, measuring the distance walked using pe-dometers can identify bulling cattle. However, the significantdifference in normal walking activity between cows means thatit is not possible to set a reliable general threshold over whichcows are likely to be in oestrus. Comparisons can only be madefor an individual cow. This requires computerisation and greatlyincreases the costs. Nevertheless, combining heat checks andpedometer detection is a highly efficient and accurate methodof detection.TV surveillanceThis method involves camera surveillance and recording of thebehaviour of cows in a confined area. It requires careful evalua-tion of a day’s recordings and relies on the subjective interpreta-tion of animals’ behaviour. 25
  40. 40. 2 Bovine Reproduction Measurement of electrical resistance of vaginal mucus – Draminsky method Changes in the electrical resistance of vaginal mucus are mea- sured with a so-called Draminsky apparatus equipped with an intravaginal probe. The method requires good records of results in individual ani- mals from previous heats and at least two readings from the current heat, to be reliable. A single reading may be misleading (standard values are provided, but there is considerable indi- vidual variation).2.2.5 Timing of insemination Fertilization of the ovum occurs in the oviduct at the junction of the isthmus and ampulla. The life span of the ovum is around 12-18 hours and its viability decreases with time. About 8 hours after service, sufficient numbers of spermatozoa have reached the isthmus of the oviduct. Capacitation of the spermatozoa is required for fertilization and is characterised by their hyper- motility and completed acrosome reaction. Spermatozoa also have a limited lifespan, therefore if insemination takes place too early, the sperm cells will die before they can fertilize the ovum. Conversely, when insemination is delayed too long, the ovum will have lost its capacity to be fertilized. Ovulation normally occurs between 10 and 15 hours after the end of oestrus. The optimum time for insemination is therefore towards the end of oestrus (see Table 7). Under practical condi- tions, cows are not observed continuously, so the end of oestrus is not apparent. Because of the limited lifespan of both ovum and sperm there is a ‘window’ of about 12 hours during which optimal conception rates are achieved. For practical purposes it is best to use the AM/PM rule: all cows seen in oestrus during the morning are inseminated during the afternoon. Cows still in heat the next morning are re-inseminated. Cows observed in oestrus during the afternoon or evening, are inseminated the following morning.26
  41. 41. Bovine Reproduction 2Table 7 Optimum time of insemination in relation to oestrus2.3 Control of oestrus2.3.1 Reasons for oestrus control The oestrous cycle can be regulated pharmacologically to in- duce or control the time of oestrus and ovulation. The main reasons for oestrus control are: - Induction of oestrus in dairy cows not observed in oestrus by 45 days post partum. - Synchronization of groups of heifers for insemination with se- men of ‘easy calving’ bulls. - Reduction of the period required for oestrus detection. - To facilitate the use of AI under extensive conditions. - Synchronization of donor and recipient cattle for embryo transfer. - Induction of ovarian activity in beef cows with lactational an- oestrus. Beef cattle Beef herds are often managed extensively and on a group basis. Oestrus detection is therefore a much less intensive activity and less accurate than in dairy herds. The presence of a sucking calf and seasonal influences can depress or block cyclical activity in beef cattle. For these reasons many beef cows do not show signs of oestrus during the 40-60 days post partum when they should be served again. Most beef herds are restricted to a specific breeding period. Cows that have not resumed ovarian activity in time, and there- fore failed to conceive, will generally be culled. 27
  42. 42. 2 Bovine Reproduction In beef herds, AI has several advantages over natural service: - Fewer bulls need to be kept. - It allows the use of high quality semen, from progeny tested bulls, thus increasing the breeding value of the herd. - More uniform calf production. In beef herds, oestrus detection is often the limiting factor for the successful use of AI. Oestrus control and synchronization can offer a solution. The use of a progestagen/PMSG system at the start of the natural breeding period stimulates and synchro- nizes ovarian activity. It thus advances and compacts the calving period compared to reliance upon natural service. The advantages of such a system are considerable: - Close supervision during the shortened calving period which reduces calf losses due to dystocia. - If weaned on a fixed date, calves will be older and heavier by sale time. - A short calving period will improve herd fertility for the follow- ing season. - Calves can be sold in batches of similar age and of consistent quality, which increases their value. - It enables and/or facilitates the use of AI and allows more rational semen management. Dairy cattle In dairy herds which practise year-round calving, cows must be managed individually and more intensively than beef cattle. With a target of one calf per cow per year, the interval between calving and conception is limited to about 85 days during which involution of the uterus must take place, ovarian activity must be resumed and oestrus detected. Generally about 25% of dairy cows have not been observed in oestrus before day 40 post par- tum. Oestrus control is used in dairy cattle for the following indications: - to induce oestrus and ovulation in cows with post partum an- oestrus in order to shorten the interval between calving and first insemination. - to synchronize donor and recipient cows for embryo transfer - to synchronize oestrus in groups of animals to improve oes- trus detection or to reduce the time required for oestrus de- tection. - to control a herd’s calving period.28
  43. 43. Bovine Reproduction 22.3.2 Methods of oestrus control The critical requirements for any effective system to control the oestrus cycle are a predictable and high frequency of oestrus and ovulation response during a specified 12-24h period, fol- lowed by a high pregnancy rate to a single pre-programmed AI after treatment. Due to changing requirements of the ovarian follicles for go- nadotrophin support during their development, it is difficult to develop one simple exogenous hormone treatment to stimulate the predictable emergence of a new wave in any animal treated, irrespective of the stage of the follicle wave at time of treat- ment. All pharmacological methods of oestrus management should be regarded as useful tools whose main objective is increase the efficiency of breeding in the herds, improve breeding or- ganization or correct some organisational deficiency. In some cases, oestrus management systems can be used as a treatment for certain reproductive disorders such as ‘silent heat’ or cystic ovarian disease. Pharmacological methods for oestrus management should, how- ever, never be perceived as replacing the proper nutrition and appropriate management of breeding cattle. In cattle with active ovaries, the oestrous cycle can be manipu- lated in three ways: - by the use of prostaglandins, to induce early regression of the corpus luteum. - by the sequential use of prostaglandins and GnRH analogues to obtain synchronized follicular development after an in- duced luteolysis. - by the use of progestagens that act as an ‘artificial’ corpus luteum. Prostaglandins Between day 6 and day 16 of the cycle (the period of natural prostaglandin F2α release) an injection of prostaglandin (Pro- solvin®, Cyclix®) will induce regression of the corpus luteum ending the luteal phase. A new follicular phase begins and the animal will come into oestrus and ovulate. The fertility at the induced oestrus is similar to that of a natural oestrus. 29
  44. 44. 2 Bovine Reproduction For the synchronization of a group of cyclic animals, likely all to be in different and unknown stages of the cycle, one injection is not sufficient. A second injection should be given 11-13 days later, because, by then, all animals should have a functional cor- pus luteum. Despite rapid luteolysis the interval to onset of oestrus after treatment with PGF2α is variable and dependent on the stage of the animal’s follicular development when treated. Animals with a functional dominant follicle are in oestrus within 2-3 days be- cause the dominant follicle ovulates at the time of induced lute- olysis. However animals at the pre-dominance phase of the wave will require 2-4 days to form a dominant follicle and hence have a longer and more variable interval to the onset of oestrus.Figure 2 Interval from PGF injection to ovulation in cattle30
  45. 45. Bovine Reproduction 2Figure 3 Distribution of oestrus in cows treated with PGF Insemination at an observed oestrus will give the best concep- tion rates and is recommended for adult dairy cows in particu- lar. Heifers show a more synchronous response and fixed time insemination at 72 and 96 hours can be used in cycling beef and dairy heifers. Because prostaglandins act on the corpus luteum, they can only be effective in cycling cattle. Prostaglandins can be used in several different ways for oestrus control depending on the intentions of the herdsman, the type of animal and the conditions on the farm. An overview adapted from Cavalieri et al. (2006) outlines the most frequently used systems (Fig. 4).Figure 4 Various systems of oestrus management with prostaglandins ɑ ɑ 31
  46. 46. 2 Bovine Reproduction ɑ ɑ ɑ ɑ ɑ ɑ ɑ Multiple dose protocols are usually designed to synchronize oestrus in whole herds with the onset of oestrus expected in most cows within 7 days of treatment. Some single dose sys- tems have also been developed with the aim of reducing the cost of treatment, but these offer far less flexibility than multidose protocols. They rely on the strategic administration of PGF2α to cows in which luteolysis is most likely to occur after treatment, and then require oestrus detection over a longer period and/or detection of a corpus luteum to ensure a high rate of response to treatment. A so-called Targeted Breeding programme was developed in or- der to improve reproductive efficiency in large dairy herds. In this system cows are systematically treated on the same day of the week, to facilitate treatment and AI on weekdays. Ani- mals receive a prostaglandin injection at 14-day intervals and are inseminated at the observed oestrus. Cows not detected in oestrus after a third prostaglandin treatment, are inseminated at a fixed time 72-80 hours after the last PGF2α injection.32
  47. 47. Bovine Reproduction 2 Application in beef cows. Due to a high incidence of post partum anoestrus in beef cows, prostaglandins are not considered to be the method of choice for oestrus management in this class of animal. Should this method be used in spite of this, it is essential to ensure that the cows are cycling and in appropriate body condition. Prostaglandins and GnRH analogues A programme sometimes known as Ovsynch (Fig 5) is primarily indicated for dairy cows and involves two injections of a GnRH analogue separated by a single administration of PGF2α. Because, in the field, synchronization is likely to be used in cows which might be at any stage of the oestrous cycle, combining GnRH with prostaglandin leads to a greater homogeneity of ovarian follicular status at the time of the induction of luteolysis. As a result, the precision with which oestrus can be predicted af- ter prostaglandin-induced luteolysis and the synchrony of the LH surge are both improved, which allows the synchronization of both follicular development and regression of the corpus lu- teum.Figure 5 The Ovsynch protocol ɑ The first administration of GnRH is given at a random stage of the oestrous cycle and causes either ovulation or luteinization of a dominant follicle, if present, in about 85% of cows (Pursley et al., 1995). The administration of prostaglandin causes re- gression of any accessory corpus luteum or luteinized follicle induced by the GnRH or indeed of any corpus luteum present following an earlier spontaneous ovulation. In cows in which the fate of the current follicle wave was altered, a new dominant fol- licle should be present on the ovary by the time of the second 33
  48. 48. 2 Bovine Reproduction GnRH treatment. Cows receiving GnRH at the pre-dominance phase of their follicular wave cycle should not have their follicu- lar wave altered and would also be expected to have a dominant follicle present at the time of the second GnRH treatment. The ovulatory response in dairy cattle has been tightly synchronized, and occurs approximately 26-32 hours after the second GnRH injection. Thus a timed insemination at 17-24 hours after GnRH should result in a high probability of successful conception (Peters et al., 1999).Figure 6 Follicular dynamics in cows treated with the Ovsynch protocol ɑ Ovsynch facilitates the precise scheduling of the first post par- tum AI, while improving reproductive performance during the early post partum period, with much saving of labour due to elimination of the need for oestrus detection. Coleman et al. (1991) and Twagiramungu et al. (1992) reported that the fertility rate of cows synchronized with GnRH and PGF2α varied between 35 and 65% and was similar to that of control animals inseminated at a first observed oestrus.34
  49. 49. Bovine Reproduction 2 Efficacy of the Ovsynch protocol The ability of GnRH-PGF2α based protocols to synchronize oes- trus and ovulation effectively is dependent on the stage of fol- licular development at the time of the initial GnRH injection. Fer- tlity obtained with the Ovsynch protocol is greatest when cows ovulate to the first GnRH injection. Vasconcelos et al. (1999) evaluated the influence of the day of the oestrous cycle on which the Ovsynch is initiated and result- ing pregnancy rates in lactating dairy cows (Table 8).Table 8 Efficacy of oestrus induction in Ovsynch protocol initiated on different days of the oestrous cycle. Vasconcelos et al. (1999) Day of oestrous cycle 1st GnRH injection 2nd GnRH injection Ovulation Ovulation 1-4 23% 94% 5-9 96% 89% 10-16 54% 85% 17-21 77% 81% Overall 64% 87% From that study it can be concluded that the conception rates should be greatest when the Ovsynch protocol is initiated be- tween days 5 and 12 of the oestrous cycle. Monitoring of the cow’s oestrous cycle to select the most promising time to initi- ate the Ovsynch protocol is, however, impractical and, in a way, acts against the whole idea of this system as being practicable regardless of the cow’s stage of the cycle. Several studies conducted during the past few years compared pregnancy rates obtained with the use of the Ovsynch protocol and other oestrus management programmes such as the use of prostaglandins (Pursley et al., 1997; de la Sota et al., 1998; Keister et al., 1998; Stevenson et al., 1999,2000; Cartmill 2001), progestagens (Gaery et al., 1998; Williams et al., 2002) and vari- ous Ovsynch programme modifications (Bartolome et al., 2002; Pancarci et al., 2002) and natural breeding (Cordoba and Fricke 2001). A meta-analysis performed by Rabiee et al. (2005) com- 35
  50. 50. 2 Bovine Reproduction pared the results reported in numerous trials with the use of the Ovsynch protocol, natural breeding, single, double or triple prostaglandin injection, Select Synch, Heat Synch and modi- fied Ovsynch. These authors concluded that pregnancy rates for Ovsynch programmes did not differ significantly from those obtained with natural breeding. Moreover the likelihood of con- ception and pregnancy did not differ significantly between the Ovsynch group and cows treated with prostaglandins. Compari- son of the probability of pregnancy in cows treated with Ovsynch, Heat Synch and Select Synch did not differ significantly. Modifications of the Ovsynch protocol Both ovulatory response to GnRH injection and luteal function following induction of ovulation with GnRH are dependent on the size of ovarian follicles at the time when GnRH is adminis- tered. Pre-synchronization and other modifications of the clas- sical Ovsynch protocol are thought to increase the probability that ovulation will be induced by the first injection of GnRH and that luteolysis and a synchronized ovulation will ensue after the administration of prostaglandin and GnRH. One of the simplest modifications of the classical Ovsynch sys- tem is the so-called Co-Synch protocol, the difference being that both the second injection of GnRH and AI are performed at the same time i.e. 48 hours after the treatment with prostaglandin (Small et al., 2000). Although most research using the Cosynch protocol has fo- cused on a 48 hour interval between prostaglandin injection and GnRH+AI, intervals to oestrus following the treatment indi- cates that a 60-64 hour interval post PGF (as used in Ovsynch), would more closely match the appropriate insemination timing for beef (Geary et al., 2000; Stevenson et al., 2000; DeJarnette et al., 2001a) and dairy (DeJarnette et al., 2001b) Reported results have been comparable with, or only slightly lower than, those obtained with the Ovsynch while the need to handle the animals is reduced (DeJarnette et al., 2003). A pre-synchronization protocol prior to implementation of the Ovsynch protocol was developed by giving two injections of PGF, 14 days apart, with the second injection given 12 days prior to36
  51. 51. Bovine Reproduction 2 the first GnRH of the Ovsynch protocol. The Pre-synch-Ovsynch protocol increased pregnancy rates by 18% (25% to 43%) in lac- tating cyclic cows as reported by Moreira et al. (2001). Post partum pre-synchronization with GnRH can also be under- taken at 7 days before the actual Ovsynch protocol. This ap- proach also has the advantage of being potentially effective in both cyclic and anoestrus cows (Thompson et al., 1999; Steven- son et al., 2000). The combination of prostaglandin and GnRH as a pre-synchro- nization treatment preceeding the classical Ovsynch or Cosynch protocol was also tried with variable success, usually resulting, nonetheless, in some improvement in pregnancy rates to the final Ovsynch AI (DeJarnette et al., 2003). Heat Synch protocol, more widely used in the US, involves re- placement of the second GnRH injection with oestradiol esters (Geary et al., 2000; Stevenson et al., 2004). Enthusiasts of this system indicate that oestradiol synchronizes the ovulation of the dominant follicle more tightly and increases the behavioural expression of oestrus in treated cows. With the growing concern for the use of oestrogens in food-producing animals, and practi- cally no possibility of using them in Europe, the application of this system is limited geographically.Figure 7 Examples of modifications to the Ovsynch protocol. Adapted from Cavalieri et al. (2006) ɑ 37
  52. 52. 2 Bovine Reproduction ɑ ɑ ɑ ɑ Injections of hCG or implants containing a potent GnRH agonist, deslorelin, have also been used to replace the second GnRH in- jection in the Ovsynch protocol to induce ovulation. The use of hCG was associated with comparable results and similar preg- nancy rates as per AI to GnRH (De Rensis et al., 2002), but imple- mentation of a protocol with deslorelin resulted in prolonged interovulatory intervals (Bartolome et al., 2004) due to the de- sensitisation of the hypothalamus (Padula et al., 2002; 2005)) and reduced pregnancy rates when a higher dose of deslorelin was used (Santos et al., 2004).38
  53. 53. Bovine Reproduction 2The Ovsynch protocol and the dose of GnRHFirst fundamental studies on the use of GnRH in Ovsynch-typesystems, and to induce ovulation, had been performed with theuse of 8mcg of the potent GnRH analogue, buserelin. Many laterstudies have involved the use of gonadorelin, but at a dose ofonly 100mcg. This dose of GnRH is the norm in the US and hasproved of considerable interest in many other countries, as itoffers the possibility of reducing the cost of treatment. But thereduced dose of gonadorelin would represent a substantial re-duction in biological potency because buserelin was estimatedto be between 40 and 200 times more potent than gonadorelin(Chenault et al., 1990). Since then, many authors have ques-tioned the efficacy of a reduced gonadorelin dose to induce ovu-lation, especially in complex Ovsynch-type synchronization sys-tems, in which the induction of ovulation in a high percentage ofcows determines both the precision of the synchronization andits efficacy. Smaller doses of gonadorelin (25mcg and 100mcg)were shown to be only partially effective (100mcg) or incapable(25mcg) of ovulating a luteal phase dominant follicle (Mihm etal., 1998).The synchronized incidence of ovulation was only 68%in cycling cows as reported by Cartmill et al. (2001), when a100mcg gonadorelin dose was used in the Ovsynch protocol. Atthe same time, Vasconcelos et al. (1999) and Fricke et al. (1998)showed comparable results, in terms of rates of induction ofovulation, when low and standard doses of gonadorelin wereused. However, some recent studies have indicated that many ofthe ovulations induced with the lower gonadorelin dose may notresult in normal corpus luteum formation. This, in turn, wouldhave a clearly detrimental effect on the subsequent maintenanceof pregnancy and pregnancy rates, in treated cows. Cordoba andFricke (2002) and Shephard (2002) reported an increased inci-dence of short cycles in cows treated with the Ovsynch protocolusing doses of 50mg or 100mcg of gonadorelin, indicative of ashortened luteal phase and failure of conception. These shortcycles occurred in both cycling and anoestrus cows. This wouldindicate that the abnormal corpus luteum formation was mostlikely to be associated with the injection of the lower dose ofGnRH having limited effectiveness on follicle atresia, ovulationand the development of the corpus luteum. 39
  54. 54. 2 Bovine Reproduction Progestagens Progestagen treatments, such as Crestar®, mimic the luteal phase of the cycle. To obtain a normally fertile oestrus, the du- ration of treatment has been set at 10 -12 days. A feature of all current progestagen-based systems is the admin- istration of oestradiol at the start of the treatment to: - shorten the life span of the corpus luteum - terminate the existing wave and induce the emergence of a new follicle. This second function of oestradiol esters used in conjunction with progestagens is especially important, as all progesterone/ progestagen-releasing systems create subluteal levels of pro- gesterone in the circulation of treated cows. These levels are sufficient to create a negative feedback and prevent a preovula- tory LH surge, ovulation and heat. Hoever, they are not able to block the LH release completely, and a small pulsatile secretion is maintained, allowing the persistence of a dominant follicle should it be present on the ovary at the start of treatment. It has been known that when the duration of dominance of the ovula- tory follicle exceeds 4 days (persistent dominant follicle) there is a progressive decline in fertility which has been attributed to a reduction in oocyte competence and an increase in embryonic loss (Diskin et al., 2002)Figure 8 Estimation of pregnancy rate as duration of dominance of the pre- ovulatory follicle increases (Diskin et al., 2002),40
  55. 55. Bovine Reproduction 2Exogenous oestradiol, administered with progesterone, sup-presses the formation of, or decreases the diameter of, thedominant follicle, when administered before or during theemergence of the wave, presumably due to suppression of FSHand perhaps LH. When follicle selection has occurred, this treat-ment results in a decrease in dominant follicle diameter withoutconsistently changing the timing of the emergence of the nextwave. Treatment of cows classified as in anovulatory anoestruswith low doses of progestagens for 6-8 days rarely induces theformation of persistent dominant follicles, as would be expectedin cows that are cycling without the presence of a functionalcorpus luteum (McDougal et al., 2004)The use of oestradiol at the beginning of a progesterone syn-chronization treatment, even when the duration of treatment isextended to 12 days, does not always guarantee that corpusluteum regression is complete in all animals at the time of, or24h after, progesterone withdrawal. Consequently, it is highlyrecommended that PGF2α be administered at, or, before proges-terone withdrawal, to ensure corpus luteum regression in thoseanimals not responding to oestradiol.One of the advantages of progestagen-based treatments such asCrestar® is that they are capable of initiating oestrous cycles inanoestrus cows. In non-cyclic cows, the progestagen sensitisesthe hypothalamo-pituitary-gonadal axis and facilitates a normallifespan of the corpus luteum. The administration of PMSG whenthe progestagen is removed, further stimulates follicular matu-ration and ovulation.The success rate of Crestar® and other progestagen-basedmethods in the treatment of anoestrus can be variable (50-70%)depending on the post partum interval at the time of treatment,the body condition of the cow and other underlying causes ofanoestrus. Nonetheless, Crestar and other progestagen-basedsystems should be seen as the method of choice in managingoestrus in beef cows, as they allow for compact breeding earlyin the season with a high percentage of cows conceiving at thefirst synchronized oestrus. This, in turn, facilitates the rapid re-presentation of cows for AI that have not conceived during thefirst oestrus, and allows of a tighter calving season. 41