Tibetan g.yag means the bull—females answer to 'bri
Domestic yaks (Bos grunniens) carry long hair across the Himalaya, Tibetan Plateau, Pamirs, and neighboring highlands. English yak borrows Tibetan g.yag for the male; females are 'bri. Related to cattle and bison within Bos, they may have split from cattle between one and five million years ago; mitochondrial studies disagree on details.
Linnaeus named the domestic yak Bos grunniens, "grunting ox," in 1766, because instead of mooing it grunts and squeaks. Nikolay Przhevalsky later called the wild form Bos mutus, "silent ox," wrongly supposing it made no sound, and a 2003 ruling by the zoological naming commission made that the usual name for wild yaks. The line may have parted from cattle anywhere from one to five million years ago and might sit closer to bison; fossils such as Bos baikalensis in eastern Russia hint at a route by which yak-like ancestors of American bison reached the Americas.
Everything about the body is built for thin, cold air. Yaks have bigger hearts and lungs than lowland cattle and keep fetal haemoglobin for life, boosting oxygen transport, while thick fat and almost no working sweat glands hold heat in. The flip side is misery in warmth: above roughly 15 °C they risk heat exhaustion. An outsized rumen lets them ferment poor forage for longer, so they get by on about 1% of body weight in food a day against 3% for cattle. Domestic bulls weigh 350 to 585 kg, cows 225 to 255 kg, and wild bulls up to 1,000 kg, all draped in shaggy hair that can hang to the ground like a skirt.
Mating runs from July to September, when bulls wallow in dust like bison and clash with lowered heads. After a gestation of 257 to 270 days a single calf is born and can walk within about ten minutes. Cows usually calve every other year, and yaks can live beyond twenty years in captivity.
Herders in Tibet and Mongolia have kept yaks for thousands of years, though the oldest dated evidence of domestication is 2,500 years old. They supply milk for chhurpi cheese and butter tea, wool, meat and ploughing power, and their dried dung is often the only fuel on the treeless plateau. Yak–cattle crosses have been recorded in Chinese texts for at least 2,000 years, yielding sterile male dzo and fertile female dzomo, and India opened a national yak research centre at Dirang in 1989.
Source: Yak
