The yak (Bos grunniens) is a longhaired humped domestic bovine found in Tibet and throughout the Himalayan region of south central Asia, as well as in Mongolia. In Tibetan, the word yak refers only to the male of the species; a female is a dri or nak. In most languages, which borrowed the word, including English, however, yak is usually used for both sexes.
Wild yaks (subspecies B. g. mutus) stand about 6.5 ft (2 meters) tall at the shoulder. Domestic yaks are about half that height. Both types have long shaggy hair to insulate them from the cold. Wild yaks can be either brown or black. Domesticated ones can also be white. Both males and females have horns.
Wild yaks can weigh 2,200 lb (1,000 kg). They usually form groups of 10 to 30 animals. Their habitat is treeless uplands like hills, mountains and plateaus between 10,500 ft (3,200 m) and roughly 18,000 ft (5,400 m). They eat grasses, lichens and other plants. During the warmest season these hardy animals live in areas of permanent snow and move lower down at colder times. Dense, close, matted under-hair as well as their shaggy outer hair insulates them. Yaks secrete a special sticky substance in their sweat which helps keep their under-hair matted and acts as extra insulation. This secretion has been extracted by Nepali tribes and used in medicine. Many wild yaks are killed for food by the Tibetans. They are now an endangered species.
Domesticated yaks are kept primarily for their milk, fiber, and meat; they are also used as beasts of burden, transporting goods across mountain passes for local farmers and traders as well as in support of climbing and trekking expeditions. Yak milk is often processed to a cheese called chhurpi in Tibetan and Nepali languages, and byaslag in Mongolia. Often the pack animals are actually crossbreeds of the yak and Bos taurus (common domestic cattle). These are known in Tibetan as dzo or dzopkyo.
Yak fiber is soft and smooth, in several colors, including shades of gray, brown, black and white. The length of yak fiber is about 1.2 inches. It is combed or shed from the yak and then dehaired. The result is a splendid downy fiber that can be spun into yarn for knitting.
Unlike cattle, yaks grunt rather than moo. Yaks can weigh over 1200 pounds and have a lifespan of 20-25 years.