A jenny is normally pregnant for about 12 months, though the gestation period varies from 11 to 14 months, and usually gives birth to a single foal. Births of twins are rare, though less so than in horses. About 1.7 percent of donkey pregnancies result in twins; both foals survive in about 14 percent of those. In general jennies have a conception rate that is lower than that of horses (i.e., less than the 60–65% rate for mares).
Although jennies come into heat within 9 or 10 days of giving birth, their fertility remains low, and it is likely the reproductive tract has not returned to normal. Thus it is usual to wait one or two further oestrous cycles before rebreeding, unlike the practice with mares. Jennies are usually very protective of their foals, and some will not come into estrus while they have a foal at side. The time lapse involved in rebreeding, and the length of a jenny’s gestation, means that a jenny will have fewer than one foal per year. Because of this and the longer gestation period, donkey breeders do not expect to obtain a foal every year, as horse breeders often do, but may plan for three foals in four years.
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