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Domestic sheep reproduction
As with other mammals, domestic sheep reproduction occurs sexually. Their reproductive strategy is very similar to other domestic herd animals. A flock of sheep is generally mated by a single ram, which has either been chosen by a farmer or has established dominance through physical contest with other rams (in feral populations). Most sheep have a breeding season (''tupping'') in the autumn, though some are able to breed year-round.〔
Largely as a result of the influence of humans in sheep breeding, ewes often produce multiple lambs. This increase in the lamb births, both in number and birth weight, may cause problems in delivery and lamb survival, requiring the intervention of shepherds.
==Sexual behavior==
Ewes generally reach sexual maturity at six to eight months of age, and rams generally at four to six (ram lambs have occasionally been known to impregnate their mothers at two months).〔 Ewes enter into estrus cycles about every 17 days, which last for approximately 30 hours.〔 In addition to emitting a scent, they indicate readiness through physical displays towards rams. Sheep may display homosexuality, which occurs in about eight percent of rams.〔 Its occurrence does not seem to be related to flock hierarchy (as some homosexual behavior is in mammals), rather the ram's typical motor pattern for intercourse is directed at rams instead of ewes. The phenomenon of the freemartin, a female bovine that is behaviorally masculine and lacks functioning ovaries, is commonly associated with cattle, but does occur to some extent in sheep.〔 〕 The instance of freemartins in sheep may be increasing in concert with the rise in twinning (freemartins are the result of male-female twin combinations).〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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