PUBERTY

Well-fed females of the European breeds commonly reach sexual maturity and begin to show signs of estrus at 6 to 8 months of age, during the autumn of their first year. If Angora doelings are small, the onset of puberty may be delayed until the second autumn. In pygmy goats, puberty may occur as early as 3 months, and occasionally even doelings of the larger breeds cycle at this young age. Introduction of a buck synchronizes puberty in a group of doelings during the breeding season. Generally, breeding should be delayed until the animal has attained 60% or more of its adult weight. Angora goats should weigh a minimum of 27 kg; larger dairy goat breeds should weigh 32 to 41 kg before being bred. If these guidelines are followed, higher conception rates and kidding percentages as well as safer parturitions will be achieved.

ESTROUS CYCLE

During the normal breeding season, August to March and especially October to December in temperate northern latitudes, goats are polyestrous. Near the equator, native breeds cycle year round but cyclicity is influenced by feed availability. Photoperiod (via secretion of melatonin from the pineal gland during hours of darkness) is an important signal for the onset of cyclicity in autumn. The end of the breeding season (transition to the anestrous period) is believed to occur because goats have become refractory to short days rather than because of a small increase in day length after the winter solstice.¹ A 60-day exposure to long days (16 hours) will end the goat’s refractoriness to short days. Introduction of a buck can advance the breeding season, as most seasonally anestrous does come into estrus and ovulate within 8 days.

The normal estrous cycle of dairy goats is approximately 20 to 21 days, while pygmy goats are variously reported as having average cycles of 18 to 24 days.² Estrous cycles are usually more erratic at the beginning and the end of the breeding season. Short cycles of less than 12 days, and often of only 5 to 7 days, are quite common, especially in young does. Short cycles are often associated with premature regression of the corpus luteum. Estrus is occasionally observed during pregnancy.

Proestrus often lasts about 1 day. It is a period when the buck or teaser closely follows the doe, but she will not stand to be mounted. Estrus, or standing heat, lasts a variable time, often 12 to 24 hours. The doe is restless, bleats frequently, and wags her tail. Metestrus is the time from refusal to mate until formation of one or more corpora lutea. Ovulation is spontaneous and is variously reported to occur 12 to 36 hours after the onset of standing heat and may be hastened by the presence of a male goat. Diestrus, the period of corpus luteum function, is the longest portion of the cycle.

Studies in the cycling Boer doe have shown that follicular waves appear, usually with 4 waves per cycle. Follicles exceeding 3 mm in diameter emerge on days 2, 7, 12, and 17 of the 21-day cycle. There are no statistical differences between waves in number of follicles or diameter of the largest follicles.³ Improved nutrition increases ovulation rate.

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