The Yak (Bos grunniens) is a ruminant mammal of the order of Artiodattili and the family of the  Bovidi, which instead of mooing emits a sort of grunt.

In Tibetan, the word “Yak” refers only to the male, while the female is called “Dri” or “Nak”. In the west, however, the name “yak” is used to refer to both sexes.

The wild Yak “Bos mutus” has a life span of approximately 20-25 years and stands up to two metres high at the withers, while the domesticated yak “Bos grunniens” is only about half this height.

The females weigh about 300 kg and have horns about 50 cm long, while the males can reach a weight of 800 kg and have horns of a length of about 90 cm, turned upwards and backwards.

The coat of the wild yak is dark brown or black, while the domesticated species may also be grey or white. Colour variations are present in limited areas of the plateau.

Like all bovids, the Yak is a ruminant herbivore; it feeds on grasses, lichens and tubers which it unearths from under the snow using its muzzle and its broad square tongue, at temperatures which often descend to below -40°C.

Its stomach is divided into four sections which enables it to eat the grass, regurgitate it and then chew it a second time.

The yaks are often used to transport goods in the high mountain areas, and also as pack animals for Alpine expeditions. In fact, despite their extraordinary bulk, the yaks have a surprisingly secure and nimble step on the steep, narrow trails, even when they are carrying loads of up to 70 Kg.

 The hooves of the Yak are formed of two enlarged toes which spread its weight, assuring it a good grip even on bare and rocky terrain, and it can traverse approximately 20-30 kilometres a day.

Yaks are very easily frightened, and always try to keep close together. This gregarious instinct allows the shepherds to lead entire herds through mountain passes blocked by the snow, so that they operate as natural snow ploughs.

The yak has the capacity to survive at high altitudes and its physiology helps in this type of acclimatisation. In fact, the Yak possesses three times as many red blood cells as normal cattle, and the cells themselves are about half the size, thus increasing the capacity of the blood to carry oxygen and enabling the animals to thrive even at altitudes where the oxygen is scarce.

The digestive apparatus too contributes to keep the animal warm at these altitudes: in fact in the rumen, the first stomach of ruminants, the food ferments at 40°C. Moreover, the peculiar structure of their thorax, made up of 14 or 15 pairs of ribs instead of the 13 typical of normal cattle, gives these animals an enhanced capacity for inhaling and expelling air, hence the Latin name used in taxonomy:“Bos grunniens”, that is “grunting ox”.