Yaks belong to the subfamily Bovinae, which also includes such medium-sized to large ungulates as domestic cattle, bison, water buffalo, and the four-horned and spiral-horned antelopes.
Conversely, yaks do not thrive at lower altitudes (ILRI).
Wild yaks can weigh up to 1,200 kilograms (2,400 pounds) and have a head and body length of 3 to 3.4 meters.
Wild yaks once had a wide distribution that included the plateaus and mountains of western China, Nepal, northern India, and parts of Mongolia (Grzimek et al.
Domesticated yaks are kept primarily for their milk, fiber, and meat, and as beasts of burden.
Many wild yaks are killed for food by the Tibetans.
Yaks are now considered a vulnerable species (Grzimek et al.
The domesticated yaks provide food (meat, milk, cheese), leather, wool, and fuel (the dung), and are used as pack and draft animals.
Yaks are used to transport goods across mountain passes for local farmers and traders as well as for climbing and trekking expeditions.
Yaks, which probably were domesticated by the first millennium B.C.E.
Yaks are known in Tibetan as dzo or dzopkyo, and in Mongolian as khainag.
The yak survives in temperatures that reach as low as -40°C (-40°F) with much of the precipitation falling as hail or snow, the lakes generally saline, and surface water scarce (Hedges 2000; Massicot 2005).
Yak fibers are soft and smooth and come in several colors, including shades of gray, brown, black, and white.
Domestic yaks mate in about September; the females may first conceive at about three to four years of age, calving April to June about every other or every third year, apparently depending upon food supply.
Wild male yaks stand about 2 to 2.2 meters tall at the shoulder, the females about one third of that size, and domesticated yaks about 1.6 to 1.8 meters.
The fur of the wild yaks tends to be black with tints of rusty-gray, and there may be grayish hairs on the muzzle (Grzimek et al.
Yaks still provide the best way to plough fields in Tibet.
Butter made of Yaks' milk is an ingredient of the butter tea that Tibetans consume in large quantities, and is also used in lamps and made into butter sculptures used in religious festivities.
A herd animal, the yak was domesticated over 4,000 years ago and are important to the society and economies of local people in the high elevation environments of Central Asia (Grzimek et al.
Often the pack animals are actually crossbreeds of the yak and Bos taurus (common domestic cattle).
More recently, sports involving domesticated yaks, such as yak skiing, or yak polo, are being marketed as tourist attractions in Central Asian countries.
Yak milk is often processed to a cheese called chhurpi in Tibetan and Nepali languages, and byaslag in Mongolia.
Ecologically, wild yaks also are important as prey species for wolves and in nutrient recycling (Oliphant 2003).