CHAPTER 79 Noninfectious Infertility in the Doe
Infections of the genital tract are seldom causes of infertility in goats,1 although infectious causes of abortion are important. Postpartum genital tract infection seldom has a residual effect during the following breeding season because of the long period between parturition and breeding, which allows time for recovery. Noninfectious causes of infertility are relatively more common in the goat, and to some extent are a result of their seasonal breeding pattern.
Aberrations of estrous cycle length adversely affect fertility through early involution of corpus luteum (CL) in cases of short cycles. Such events as puberty, time within the breeding season, introduction of the male, and hormone therapy may result in short estrous cycles that are infertile. Extended cycle length may likewise cause infertility or be a result of infertility, as in cases of early embryonic death.
Young does should have reached about 65% of their mature body weight by the time of first breeding. This may not occur during the calendar year of their birth, if they were born late in the kidding season, late spring or early summer. The next year these does are of sufficient size to successfully breed. Does born early in the kidding season, late winter or early spring, should have reached adequate size to start breeding during the fall that same year. Restricted feed intake around the time of puberty may slow development or result in anestrus. Young, lightweight does have an increased frequency of abnormal first cycles, either short or long.2 Although mating may occur during these first cycles, pregnancy would not be expected to be established. It is prudent to allow young does to cycle two or three times prior to breeding for the first time.
Short estrous cycles are a natural part of the onset of the breeding season.3,4 These short cycles may be associated with ovulation but followed by a CL that is short-lived. These short cycles have a luteinizing hormone peak of low amplitude, which may be responsible for defective CL formation. Camp and associates,5 in a study of short estrous cycles, found that 86% of these cycles occurred early in the breeding season and that 55% appeared to be anovulatory. They found that there was no difference in the duration of estrus for short (2.9 ± 0.3 days) versus normal (2.8 ± 0.8 days) cycle groups.
Aberrant cycle length also occurs at the end of the breeding season when does are in transition to the anestrous season. These cycles typically have an extended length. At the end of the breeding season, nonreturn to estrus is not trustworthy to detect pregnancy because long estrous cycles are likely to occur.2 Some does enter an anestrous period after late breeding and may be mistakenly assumed to be pregnant by their owners.
During the late transition season, novel introduction of a male to a group of females will initiate estrus and cyclicity within the group. Some 97% of females ovulate about 3 days after introduction of the male, but 75% experience short luteal phases of 5 days, followed by a second ovulation with estrus in 89%.6 Only 68% of the initial ovulations are accompanied by estrus. Fertility at first estrus following exposure to the male is quite variable, but it seems that the shorter the time elapsed from male introduction to first estrus, the lower the fertility.2 Fertility returns to normal at the second estrus.
The use of hormone therapy during the breeding season has resulted in alteration of the normal cyclic pattern in some goats. Pregnant does given 5 mg prostaglandin F2 alpha to induce abortion often experience a short cycle following the postabortion estrus.4 These short estrous cycles are associated with delay and decreased magnitude of the preovulatory luteinizing hormone. Armstrong and colleagues7 reported that goats experience a high incidence of premature luteal regression following superovulation with pregnant mares’ serum gonadotropin. This is usually associated with low embryo recovery. Dexamethasone given in repeated 10 mg daily doses, starting during diestrus, has been shown to extend the estrous cycle by a mean 8.75 ± 0.96 days.8 Corticosteroid therapy causes a progressive decline in luteinizing hormone response to gonadotropin-releasing hormone and may result in the development of cystic follicles.