Since yaks cannot survive below 3,500 meters (10,500 feet), they are found at higher altitudes, usually above 4,500 meters (12,500 feet) and sometimes, as high as 6,100 meters (18,300 feet). Unique hemoglobin in the yak's blood may have assisted the creature in adapting to high altitudes. Yaks are rather large creatures, standing nearly 6 feet tall at the shoulder, with male adults weighing over a ton. Females of the species tend to weigh about a third of that. An endangered species, yaks are not helped by the fact that they bear only one young after a nine month gestation period, and that baby yaks need a full year to ween before they can survive on their own.
Yak is a main source of livelihood for the high altitude residents in Bhutan .Herder's garments and tents for shelter are made from yak fibre. Pack yak are an important means of transport in the alpine region. In summer pastures, above the tree line, yak dung is the only source of fuel. Yaks also play special roles in the religious and cultural life of the herder's society. They are closely tied to the social customs and identity of the herder communities.
Yak herders
In order to improve yak productivity, the government has been procuring and distributing yak bulls from one region to another. Artificial insemination was tried with imported yak semen from China but achieved limited success mainly due to inaccessibility of yak areas. The herders frequently exchange their breeding bull with neighbouring farmers to reduce inbreeding in the herd. Herders without their own breeding bull obtain services from the bulls of their neighbouring herdsmen. In exchange for the service, the bull owners usually receive payment in kind. There are well-defined criteria for selecting yak breeding bulls in their herd .
Yaks are herded by a special group of people called Zhops (pass dwellers). Zhops live a transhumant and nomadic life with their yak, between altitudes of 3,000-5,000 m. Residents in nine of Bhutan's 20 districts (approximately 10 percent of national population) are involved in yak husbandry.