Puberty

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.

Season

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.

Male Effect

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.

Hormone Therapy

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.