Massive ox (Bos grunniens mutus) of high Tibetan plateaus. Bulls grow to 6 ft (1.8 m) at the shoulder hump. The wild yak's hair is black and short, except for a long, shaggy fringe on the flanks and tail. The horns spread outward and upward; the head is held low. Wild females and young live in large herds; mature bulls form smaller groups. Yaks graze on grass and require much water, eating snow in winter. Wild yaks are now endangered. Domestic yaks, which breed freely with domestic cattle, are used as pack, draft, milk, and beef animals. The hide provides leather; the tail, fly whisks; the fringe hair, ropes; the dried dung, fuel.