The immune system is an intricate complex of cellular, molecular, and genetic components, strongly interrelated for providing a defense against foreign organisms or sub- stances and aberrant native cells (Nickel et al., 1981 ). The defense is the so - called “ immune response. ” The foreign organisms or substances constitute the “ antigen, ” and the result of the reaction of the immune system is the produc- tion of “ antibodies. ” A very specifi c reaction occurs between the antigen and the antibodies, at the end of which an “ active immunity ” is established. Also the active immu- nity can be obtained by inoculation in a healthy organism with an attenuated or killed antigen (vaccine). In an indi- vidual already attacked by an antigen, specifi c antibodies obtained from a donor (called antiserum) can be inoculated and can act immediately against the antigen. This is the
so - called “ passive immunity. ” Comparable to passive immunization is the use of colostrum in the fi rst several days of the neonates. The colostrum contains antibodies from the mother ’ s immune system. In all mammals, the lymphatic system (which is part of the cardiovascular system) is deeply involved in immune reactions. The lymph nodes, the lymphatic structures in the mucous mem- branes, thymus, spleen, and bone marrow are the structures producing antibodies and immune reactions resisting the action of the antigens. They all contribute to the defense mechanism of the organism. Those lymphatic structures in the mucous membranes are located in the pharynx, larynx, intestine, prepuce, vagina, etc.
The immune system consists of diverse organs produc- ing different types of antibodies and maintaining the integ- rity of the body. The lymphocytes, macrophages, and other “ cells ” possess immune properties. The thymus and the bone marrow produce T - and B - lymphocytes, respectively, which are later produced in the lymph nodes, spleen, and tonsils. The macrophages belong to the reticulo - endothelial system (in the reticular connective tissue) and have the property of phagocytosis (inclusion of the antigen into their cells and breaking it down) and storage (of the phagocytized material). For details please consult books describing the immunity and the immune system, such as “ Veterinary Immunology ” by Tizard (2000) and “ Veterinary Immunology ” by Outteridge (1985) . Even in the current texts, the caprine immune system is not addressed directly.
SUMMARY
This chapter, Functional Anatomy of the Goat, was written as basic knowledge. It covers the essential information to start with, for any direction the reader will take to pursue a professional education, to be enrolled in a graduate school, or to start a research program. The anatomical structures are described in a systemic and systematic order, using the international anatomical nomenclature. For details, different sources of information are suggested.
The 15 sections of this chapter cover the anatomy of the goat in different proportions, based on the role (functional- ity) of the anatomical structures. Thus, larger spaces are attributed to the horn and digital organ; to the cardiovas- cular, respiratory, digestive, and reproductive systems; to the sense organs; and to the mammary gland.
The chapter is illustrated with a minimum of original drawings. Additional fi gures may be seen in the cited lit- erature (Constantinescu, 2001 ). The additional suggested readings are provided for the reader to look for more details.
Philadelphia, PA .
Smith , M.C. and D.M. Sherman . 1994 . Goat Medicine , Lea & Febiger , Philadelphia, PA .
Tizard , I.R. 2000 . Veterinary Immunology. An Introduction , 6th ed. , Saunders , Philadelphia, PA .
ADDITIONAL SUGGESTED READINGS
Barone , R. 1976 . Anatomie Compar é e des Mammif è res Domestiques , Laboratoire d ’ Anatomie É cole Nationale V é t é rinaire , tome 3 - é me fascicule premier , Lyon .
Simoens , and N.R. de Vos . 2007 . Illustrated Veterinary Anatomical Nomenclature, 2nd ed. Enke Verlag , Stuttgart . Schatten , H. and G.M. Constantinescu . 2007 . Comparative Reproductive Biology , Blackwell Publishing , Ames, Iowa . Stedman ’ s Medical Dictionary . 2000 . 27th ed. Lippincot ,
Williams & Wilkins , Baltimore, MD .
Breeding season — when does and bucks are sexually active and bred to produce offspring.
Estrous cycle — the sexual cycle of the doe, from one estrous period to the next, and the period is on average 21 days. Ovulation — the shedding of an ovum by a mature ovarian follicle.
Postpartum anestrous period — interval following kidding during which the doe shows no signs of estrus. Synchronization — hormonal induction of estrus to occur within a limited period of time.
Multiple ovulation and embryo transfer — the induction of superovulation, fl ushing evaluation, and transfer of embryos to recipients.
Accelerated kidding — when does are managed to breed three times in 2 years. Dystocia — diffi cult births where assistance must be given.
OBJECTIVES
By completing this chapter, the reader will acquire knowledge on:
•
The reproductive potential of the goat•
The principles and reproductive physiology involved in applied reproduction of goats•
The different physiological stages in the doe and factors that play a role•
The seasonal sexual activity in the doe and buck•
The insight into the reproduction physiology of the male•
The principles and the application of certain reproductive technologies in the doe•
The pregnancy diagnosis in the female•
The most important aspects to be considered in a goat reproduction program139 INTRODUCTION
Roughly 95% of the 850 million goats in the world are found in the developing countries of Asia, Africa, and South America. These goats are multipurpose animals that provide a vast range of products, including meat, milk, skins (leather), and fi ber; and for too long, the role of goats and their contribution to the livelihoods of people have
been ignored (Peacock et al., 2005 ). In recent years, the demand for goat products has also increased in the devel- oped countries, accompanied by the number of commercial goat farmers. As reproduction can be seen as the corner- stone in any animal production chain, its importance cannot be overemphasized. This is also relevant to the goat. Thus, to help exploit the restricted goat resources
and help alleviate the demand for animal protein via human consumption, it is essential to increase the reproduction effi ciency (conception, fecundity, and kidding rate) also in goats (Greyling, 1988 ).
The level of reproductive performance depends on the interaction between genetic and environmental factors, but it is particularly susceptible to the infl uence of the latter. These factors include nutrition, ambient temperature, stocking density, age groups, etc. Although goat breeds have an excellent ability to accommodate and adapt to fl uctuations in environment, this often involves some degree of reproductive failure (Riera, 1982 ; Zarazaga et al., 2005 ).
Reproductive effi ciency in does is determined by many different processes. These processes include the length of the breeding season, cyclic activity, ovulation rate, fertilization rate, the postpartum anestrous period, growth, and viability of the offspring. The reproductive effi ciency as such is then measured and expressed in terms of kidding rate, kidding interval, weight of kids born or weaned, or length of the reproductive life of the dam (Greyling, 1988 ). With the goat ’ s general hardiness, high fecundity, good mothering ability, and extended breeding season, this specie is an ideal candidate for applied or manipulated reproduction physiology to, among others, increase the reproduction effi ciency (Devendra and Burns, 1983 ).
However, to manipulate the reproductive effi ciency of the female goat using accelerated breeding techniques such as artifi cial insemination (AI), synchronization, and super- ovulation or multiple ovulation and embryo transfer (MOET), a thorough knowledge of the hormonal status and physiology of this animal is essential. The reproduc- tive physiology must be seen in conjunction with the func- tional anatomy for reproduction addressed in Chapter 6.
PUBERTY
Female
One of the fi rst factors important in determining lifetime production performance in the goat is puberty. Puberty occurs as a consequence of the activation of the gonado- trophin surge mechanism by the positive (stimulatory) feedback action of oestradiol on the hypothalamus. In the female, puberty is defi ned as the stage when the doe starts and exhibits regular cyclic estrous activity. So for example, some of the information on puberty relates to body weight and age of the doe at fi rst standing estrus. It must be kept in mind that many of the endocrine mecha-
nisms leading to ovulation and fi rst estrus are capable of operating long before they are called upon to function (Greyling, 2000 ; Zarazaga et al., 2005 ).
Generally, breeding in does should be delayed until the animal has attained 60 – 70% of its mature body weight. Angora goats should weigh a minimum of 27 kg, while the larger dairy goat breeds should weigh between 35 and 45 kg before breeding. These weights must however not be con- fused with the weight at puberty. There is good evidence of inadequate nutrition (besides retarding growth rate) having adverse effects on pituitary function and hence gonadotrophin (sex hormone) secretion in the immature animal. Once a critical body weight is reached, differences in live weight have little infl uence on the time of onset at puberty. In most goat breeds, the does are pubertal between 5 and 7 months of age (Smith, 1980 ; Jainudeen et al., 2000 ). The potential for improved reproductive effi ciency increases as the age at fi rst kidding decreases, but manage- ment practices are often introduced to delay mating for full development of the female, to increase the conception rate, the frequency of multiple births, and to assure the survivability of the offspring. It is important to realize that climate, nutrition, and the presence of the male are factors that could modify the age at puberty in the doe. There is also ample evidence to indicate that seasonality is an important factor in the attainment of puberty in goat kids (male and female). The onset of cyclic activity is usually stimulated during the season of shortening days and its termination occurs during the lengthening (photo- period) days. The presence of the buck, besides modifying the age of puberty in the goat, also infl uences estrous behavior, with some degree of synchronization of estrus. There may be two distinct physiological actions involved in the presence of males, namely a neurohormonal action, which advances the preovulatory discharge of LH, and a solely neural action, which gives rise to the “ male effect ” (Riera, 1982 ; Chemineau et al., 1992 ; Gordon, 1997 ; Bukar et al., 2006 ).
The mean body weight at fi rst estrus or puberty for Boer goat female kids born in January (summer) and August (late winter) is 31.3 kg and 27.4 kg, respectively, while that in the Saanen is 30.0 kg for animals born in March/April (spring). The mean age at puberty in Boer goat does born during late winter and midsummer was recorded as 191.1 and 157.2 days, respectively. Kids weaned in autumn (during the natural breeding season) generally exhibited estrus signifi cantly earlier than animals weaned outside the natural breeding season. It would thus seem as if season is one of the main cues for initiating the onset of puberty. The age at the onset of puberty in the Boer goat compares
nifi cant increase in testosterone production and subsequent spermatogenesis. This phenomenon occurs at 4 – 6 months of age. Factors that affect the onset of puberty include photoperiod and nutrition. Sexual maturity (when bucks can be used for breeding) is generally at approximately 18 months of age (60 – 80 kg, depending on the breed).
Both internal and external cues affect time of puberty, and it is diffi cult to isolate a single factor involved in the attainment of puberty. Generally a sequence of events is involved in the process of sexual maturation and an inter- action possibly exists between the male effect, seasonality, and nutrition (Greyling, 1996 ; Nishimura et al., 2000 ; Todini et al., 2007 ).
SEASONALITY AND THE BREEDING SEASON