yak(redirected from Bos grunniens grunniens)
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(Poephagus grunniens), a ruminant of the subfamily Bovinae. The yak occurs in the wild only in Tibet.
A large animal, the wild yak sometimes reaches a height of 2 m and a weight of 1 ton. The body is massive. The legs are relatively short, and there is a hump at the shoulders. The long, rather slender horns of the males spread outward, forward, and then upward. The horns of the females are shorter than those of the males. The black-brown coat is thick, and there is a warm undercoat. The hair is especially long on the abdomen, chest, and legs, forming a “skirt” that keeps the animal warm when it lies on the snow. The tail is covered with long, coarse hair.
The wild yak inhabits forest-less high-desert plateaus. It is solitary or lives in groups of two or three. It feeds on herbaceous vegetation, which it can obtain even from under the snow. Mating occurs in September or October, with a single young born in June and July. The wild yak avoids contact with human habitation; hence, crowded out by domestic herds, it is decreasing alarmingly in number.
Domesticated yaks are raised in high-mountain regions of China and Mongolia. In the USSR they are raised in the Gomo-Altai AO, the southwestern Tuva ASSR, the Kirghiz SSR, and the Buriat ASSR. They are smaller than wild yaks. Adult males weigh 400–450 kg, and adult females 270–300 kg. The annual milk productivity is 300–350 kg of marketable milk per year; the fat content of the milk is 6–7 percent. The lactation period is 170 to 180 days; the calves are suckled. Yaks pasture under the open sky year-round. They are valuable work animals, able to easily carry loads of as much as 140 kg on mountain trails. Yaks are also kept for their coarse-fibered flavorful meat. Hair clippings yield as much as 3 kg per year; the hair is used to manufacture coarse cloth and rope. Hybrids are obtained by crossing with cattle; bulls are fertile in the third or fourth generation. The hybrids exceed yaks in weight and productivity.