Rapid growth of the yak calf in the first few months of its life is a prerequisite for survival over the first winter and for a good start to its continuing growth in the following year. Thus, animals that are born early in the warm season have a better chance than those born later. Calves with exclusive access to the milk of their dams have the best opportunity for growth, especially if they are allowed to graze at night alongside their dams - but such night grazing is not common practice. Calves with dams that are milked once daily generally grow appreciably better than those with dams milked twice daily, not only because they have a somewhat greater milk intake but because they have perhaps an extra four to five hours daily available for grazing alongside their dam. Males become heavier than females, but they grow relatively more slowly in the early years of life and continue to grow for longer. Typically, in China, males are brought into the adult herd at six years old and females at four years; but in some other countries this occurs a year earlier. Breeds of yak appear to differ in size and growth rate, though this observation is usually confounded with differences in location. There is much seasonal variation in body weight.
Heavy losses in weight over winter and spring are recovered during the following warm season, when young animals recover what they have lost and make all their additional growth. This pattern is repeated each year. Approximately 25 percent of the weight at the end of the warm season normally is lost over the succeeding winter and spring - except in the first year of life when that loss is only about 12 percent. Linear body dimensions of the animals reach their final size at an earlier age than does body weight - although there are differences among the dimensions in age at maturity. As must be expected, the linear body dimensions show less seasonal variation than does body weight.
Milk yield in yak is low and seasonal. The amount produced is only what would normally be needed for the good development of the calf. However, as milk is an important product for the herdsmen, milking is done at the expense of the calf - though once-a-day milking has relatively little adverse effect on calf growth compared with twice-a-day milking. There are reported differences in milk yield among breeds, but these are breeds kept at different locations. There are no specialized milk strains of yak. Though the milk yield is low, the solid content, and fat in particular, is high (6.5 percent is not uncommon).
The single most important factor influencing milk yield is the supply and quality of grass in the warm season of the year. Daily yield most often reaches its peak in August. Supplementary feeding, though effective in maintaining yield out of season, is not practical or economic under most present conditions.
Yak do not dry off when milking ceases at the end of the warm season, and the calf, when present, continues to take some milk. Lactation can continue into a second year without pregnancy recurring and reach between one half and two thirds of the yield in the year of calving. The yak does not readily let down its milk without stimulation from the calf, and milking is quite strenuous because of the strong sphincter muscles in small teats.
Yak meat is obtained mostly from animals that are surplus to other requirements. Surplus males are castrated - usually at a fairly mature age - and slaughtered as steers. Meat quantity is determined largely by body weight. Animals are normally slaughtered in September or October when they are in the best and fattest condition.
Dressing percentages commonly range from around 45 percent to 58 percent, the ratio of lean to bone from as little as 3:1 to as high as 6:1, depending on the source and condition of the animal. The fat content of the carcass and the fat content within the meat are generally low.
Hair is an important by-product of the yak. Quantity produced varies with the age and size of the animal, with breed and sex and with the method of harvesting. There are two distinct types of fibre - down fibre and coarse hair - differing in diameter, length, degree of medullation and other properties; there is also an intermediate "mid-type" hair. The proportions of the different types of hair vary on different parts of the yak body. The proportion of down fibre is high in calves and declines as the animal gets older. Down fibre grows as additional protection for the yak over winter and has to be harvested prior to being shed in the early summer. The down fibre is much valued for textiles.
Large numbers of hides are produced and processed, but quality is not regarded as good as from other cattle. Weights of hides vary with but represent around 6 percent of live weight. Thickness of skin varies with the age of the animal and the part of the body.
Yak steers are used widely for carrying packs, for riding and, in some areas for cultivating land. Yak have high endurance for work and can carry heavy loads in relation to their own body weight. They are particularly valued for their ability as pack animals to cope with dangerous terrain and marshy land at high elevations.
Improvements in production
Interventions in breeding, animal and herd management, feeding, housing and pasture management can all be used to try to improve output. However, it is important to ensure the cost-effectiveness of such measures.