The domestic yak is a long-haired domesticated bovid found in Asia. These are heavily built animals with a bulky frame, sturdy legs, rounded cloven hooves, and extremely dense, long fur. They have small ears and a wide forehead, with smooth horns that are generally dark in color. In males (bulls), the horns sweep out from the sides of the head and then curve forward. Domestic yaks can be quite variable in color, often having patches of rusty brown and cream. Some individuals can be white, grey, brown, roan or piebald in color. Both sexes have long shaggy hair with a dense woolly undercoat over the chest, flanks, and thighs to insulate them from the cold. Especially in bulls, this may form a long "skirt" that can reach the ground. The tail is long and horselike rather than tufted like the tails of cattle or bison.
Domestic yaks are found throughout the Himalayan region of the Indian subcontinent, the Tibetan Plateau, Northern Myanmar, Yunnan, Sichuan and as far north as Mongolia and Siberia. They inhabit alpine meadows, alpine steppe, and desert steppe. They require large areas of grassland with small shrubs and other vegetation.
Domestic yaks are active during the day. They are social and live in herds of about 10-20 animals. These herds usually consist of females and their young. Males may live solitary or form small bachelor herds. During cold nights and in snowstorms, yaks huddle together, positioning the calves in the center. Yaks are well adapted for living in high altitudes; they have larger lungs and heart than cattle found at lower altitudes. Domestic yaks communicate with each other with the help of grunts. Unlike cattle, they do not produce the characteristic bovine lowing (mooing) sound, which inspired their scientific name variant, Bos grunniens (grunting bull).
Domestic yaks are polygynous, which means that one male mates with more than one female during the breeding season. Yaks mate in the summer, typically between July and September, depending on the local environment. For the remainder of the year, many bulls wander in small bachelor groups away from the large herds, but, as the rut approaches, they become aggressive and regularly fight among each other to establish dominance. In addition to non-violent threat displays, bellowing, and scraping the ground with their horns, bull yaks also compete more directly, repeatedly charging at each other with heads lowered or sparring with their horns. Bulls also wallow in dry soil during the rut, often while scent-marking with urine or dung. Females give birth to a single calf between May and June; the gestation period lasts around 257-270 days. The newly born calf is able to walk within about ten minutes of birth. Females typically give birth only once every other year, although more frequent births are possible if the food supply is good. Calves are usually weaned at one year of age and become independent shortly thereafter. Females generally give birth for the first time at 3-4 years of age and reach their peak reproductive activity when they are 6 years old.
Yaks are among the most important domesticated animals in central Asia. They are thought to have been domesticated during the first millennium B.C in Tibet. Their great ability to survive at high altitudes contributed to making human settlement of the Tibetan Plateau possible. Domesticated yaks have been kept for thousands of years, primarily for their milk, fibre and meat, and as beasts of burden (working animal). Yaks transport goods across mountain passes for local farmers and traders as well as for climbing and trekking expeditions. They also are used to draw ploughs. Yak's milk is often processed to a cheese; butter made from 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. Currently, in Central Asia's highlands, there are over 14 million domestic yaks.