CHAPTER 82 Reproductive Health Program
Goats are important livestock animals throughout the world. This is in part related to their ability to survive on suboptimal forage in more arid environments, combined with their smaller size, shorter gestation period, and increased litter size, particularly when compared to bovids. The Food and Agriculture Organization (FAO) figures for 2004 estimate the total goat population in the world at approximately 780 million animals.1 Even in the United States, where goat production is lower than in other parts of the world, the 2004 kid crop was estimated to be 1.67 million animals.2 Goats in the United States were used primarily to produce meat (1.97 million animals), goat’s milk (283,500 animals), and fiber (274,000 animals).2
The success of any goat production operation depends upon optimizing reproductive health. Although the basic requirements for good reproductive health are similar in all types of goat operations, there are some differences in the reproductive demands and husbandry practices, particularly for dairy animals as compared to goats raised for meat and fiber. Areas of importance for reproduction in goats include how the herd is housed and pastured, the nutritional requirements of the herd relative to type of production and breed, disease and parasite control, reproduction program, and special requirements for dairy operations.
Most goats reared for meat and fiber are housed on pasture or range. Some access to protective shelter or housing is preferable, particularly during the kidding season. Goats are unlike sheep; whereas newborn lambs immediately follow the dam, does naturally hide their kids for the first few days after birth, thus making newborn kids vulnerable to predation.3 This also means that pastures should be carefully checked for young kids if moving the herd during the kidding season.
Unless breeding is being timed or synchronized, it is common to run the bucks with the does, allowing breeding to occur throughout the breeding season.4 A stocking rate of 1 buck to 50 does is usually suggested, although stocking rates as high as 1 buck to 250 does have been reported.5
Dairy operations usually keep goats housed indoors, sometimes with access to pasture. If bucks are kept on the premise, they are separated from the does so that estrous synchronization and breeding can be controlled. Bucks that are kept isolated from females can be used to synchronize the does via a pheromonal phenomenon known as the “male effect” or “buck effect.”6–8 Some goat dairies do not keep bucks on the premises, but rely upon artificial insemination (AI) for breeding and to increase genetic variability within the herd.9
Bucks that live together establish a dominance hierarchy. Fighting among bucks to establish this hierarchy can be severe, particularly during the breeding season. In addition to acquiring physical injuries, bucks housed with females or near females during the breeding season can lose significant amounts of weight by fighting among themselves rather than eating. Dominance behavior in group-housed bucks usually takes the form of rearing and fighting, but can also include homosexual behavior during the breeding season.10 Although this behavior has the potential to spread disease, venereal disease among bucks is not as great a concern as it is in rams where Brucella ovis is spread by this behavior.5 Subordinate bucks can have their breeding potential reduced by dominant bucks. If more than one buck is housed with does during the breeding season, the dominant buck can physically interfere with other bucks attempting to breed, a phenomenon sometimes called the “dominance effect.” Even when separated from dominant bucks, subordinate bucks can be psychologically intimidated from breeding does if the dominant male is close by (“audience effect”). Subordinate bucks can be induced to breed by putting them in a pen with females situated at a distance away from the dominant buck, or by housing the male with a group of smaller or younger bucks (personal communication, Dr. William Gavin, Stephen Blash, GTC Biotherapeutics).
Does will also form dominance hierarchies. If a group contains both horned and de-horned or polled does, the does with horns will most often become the alpha goats. Dominant does will sometimes physically attempt to keep the most subordinate does from feeding. This is particularly true in situations in which hay and grain is delivered in stationary feeders that can be “patrolled” or defended by the alpha doe. In some situations it may be necessary to separate the alpha does from the subordinate does during feeding to ensure that subordinate does get their fair share of the feed, and that the alpha does eat rather than “patrol” the feeder.11
Because of the young age at which goats can attain puberty, it is important to separate young bucks from does at an early age.12 Bucks as young as 3½ months of age have been known to impregnate does, including their siblings or dam.
Good nutrition is necessary for goats to successfully reproduce. It is suggested that goats attain two thirds of their adult weight before being used for breeding.5 Breeding young does that are very small in stature can result in dystocias, particularly in small does carrying large singletons. It is also possible to stunt the growth of the doe by breeding at too young an age.
It is important to understand the nutritional requirements of the breeds being kept to prevent overconditioning as well as underconditioning of animals. Meat breeds such as Boers or Spanish goats can convert feed to muscle mass at a far greater efficiency than most dairy breeds (e.g., Saanens, Alpines) and therefore require less feed for maintenance. This can be problematic when different breeds are housed together, or when dairy maintenance regimens that include grain are used for meat breeds.
Meat and fiber goats can obtain adequate nutrition when reared on good quality pasture. Goats are selective browsers and usually avoid eating toxic plants, but problems can arise if the pasture is marginal, or if vegetation is sparse during dry periods. Goats will then consume forage that can result in reproductive problems. A study in Texas showed that bucks grazing pastures containing plants with high levels of dietary phenolic amines such as those found in shrubs of the genus Acacia had a significant reductions in serum testosterone, scrotal circumference, and semen volume.13 Other toxic plants that can lead to reproductive problems include Lupinus formosus, Conium macilatum, Nicotiana tabacum, and Veratrum californicum.3
Breeding bucks need to be in good body condition. A body score of 3.0 to 3.5 has been suggested.12 It is important that good body condition be attained prior to the breeding season, as bucks tend to lose weight during this time, particularly when group-housed. Feeding regimens should be changed with care, as there can be problems associated with increasing nutritional planes in bucks. Such increases in feeds are most commonly seen in bucks or wethers being raised for the meat market when additional feeds are used to increase muscle mass or decrease the time needed to attain market weight. A variety of substances have been added to a basic grass diet to increase weight gains including grains, and by-products such as soy hulls, corn gluten, wheat middlings, etc.14 Diets that result in high protein can lead to ulcerative posthitis, a condition related to production of high levels of ammonia in the urine that, if severe, can reduce a buck’s willingness to breed.3,5 Diets that are high in phosphorus can change the calcium-to-phosphorus ratio to less than 1.5:1 to 2.0:1 and result in the formation of struvite uroliths within the urethra and bladder. Feeds that are high in calcium, such as alfalfa or subterranean clover, can also contribute to the formation of uroliths. Access to clean water, and addition of salt and ammonium chloride to the diet can help prevent the production of uroliths in males.12
Feed regimens are important reproductively for females as well as for males. Does should be in good condition prior to breeding. Body scores of 2.5 to 3.5 (out of 5) have been suggested as optimal.12 Like ewes, does can respond to increased nutrition just prior to the breeding season (flushing) with an increase in the average number of ovulations. But overfeeding of does, particularly dry does, is to be avoided. Overfeeding of grain can result in obese females that exhibit high body condition scores and are more prone to dystocias, in part related to fat deposits in the area of the birth canal. Overconditioned females are also predisposed to develop pregnancy toxemia.15,16 Inadequate nutrition can also interfere with reproduction. Low nutrition can result in poor ovulation rates or cessation of cycling. When cycling does were fed a restricted diet (30% of requirement) they did not ovulate in response to an estrous synchronization regimen, exhibiting a reduced frequency of luteinizing hormone (LH) pulses.17
Diseases can affect reproductive health in a number of ways. Most diseases of goats, such as pneumonia, have at least an indirect effect on reproductive health through reduction of appetite, production of fever, loss of weight, or reduction of ambulation. A sick animal is less likely to breed and to carry pregnancy to term. Chronic ill-nesses such as Johne’s disease, caseous lymphadenitis, and caprine arthritis-encephalitis (CAE) can sometimes have insidious effects on reproductive health. Caprine arthritis-encephalitis is a slow lentivirus of particular concern to the dairy goat industry. Early CAE can negatively impact milk production while producing few clinical signs.18 The prion diseases, including scrapie and the transmissible spongiform encephalopathies, not only cause a wasting disease but are also of concern for public health.19
The set of diseases that most directly impacts goat reproductive health consists of those that cause abortion. Abortion occurs sporadically in goats, but endemic infectious abortion has the greatest economic impact. Many infectious agents have been incriminated in goat abortions, but Chlamydia psittaci, Toxoplasma gondii, Coxiella burnetii, and Mycoplasma mycoides are the most commonly diagnosed.16 Ovine chlamydial vaccines provide moderate protection against abortion. Toxoplasmosis is best prevented by controlling cat populations, especially by preventing reproduction, and also by control of rodents. Ionophores fed to dry does may decrease abortion in exposed individuals. The control of Mycoplasma infection requires a multifactorial approach with detection of carriers, control of milk transmission, and culling of identified carriers.
Chlamydia is the most common cause of infectious abortion in high-density confinement goat dairies. Does exposed any time (including neonates) prior to day 90 of gestation are susceptible to abortion of that pregnancy, while does exposed from day 100 of gestation onward are at risk of aborting during the next pregnancy due to the long incubation period required to develop necrotic plancentitis that leads to abortion. Although Chlamydia infection is traditionally associated with last semester abortion, experimental infection around day 60 of gestation, when the organism first crosses the placenta, may result in fetal death with resorption or abortion.16
Disease can be controlled by good husbandry practices and vaccination programs. If animals are housed indoors, particular attention should be paid to keeping animal densities from becoming too high, having a good waste removal program, and having adequate ventilation. Vaccination programs vary depending upon region and country, but usually include vaccines for Clostridium perfringens types C and D, and Clostridium tetani.3,12 If rabies, chlamydiosis, or leptospirosis is endemic, appropriate vaccines are also included. In areas deficient in soil selenium, vitamin E and selenium are administered to prevent white muscle disease.20 It is important to schedule vaccinations to pregnant does 3 to 4 weeks prior to delivery to ensure adequate antibody production in colostrum.3,12
Large parasite loads can induce chronic weight loss, diarrhea, and anemia in animals and thereby reduce reproductive potential.21 This is of increased concern with the development of strains of parasites such as Haemonchus contortus that have become resistant to anthelmintic treatments.22 Understanding the ways in which choice of anthelmintic drugs and timing of treatments for parasite control contribute to selection for resistance (e.g., frequent use of the same class of anthelmintic) are important to prevent the development of resistant parasites.23 For animals on pasture, knowledge of parasite cycles combined with schedules of pasture rotation may be effective in helping reduce parasite loads.23 Investigations are ongoing to find genetic markers for goats that are more resistant to parasite infection, as well as ways to increase natural resistance. For example, it has been suggested that high-producing dairy goats may benefit from supplemental protein in the diet as a way to increase resistance to nematode infection.24