Physico-chemical properties, gross composition and nitrogen fractions of milk from Chinese Qinghai plateau yak {Bos grunniens) reared in two different altimetric zones

摘要

The aim of this work was to characterise the gross composition and the nitrogen fractions of the milk from Qinghai plateau yak, and in particular to evidence possible differences between milk from yaks reared at very high altitude and milk from yaks reared at less high altitude. Moreover, a comparison was made between Qinghai plateau yak milk and the milk from cow and ewe. Four different yak farms, located in different zones of the Chinese province of Qinghai, were considered. Two of them were located at more than 3000 m, and other two at less than 3000 m. The research was carried out on herd milk samples, representative of all the farm production. For each farm, four samplings were carried out, in 4 different months. The results indicate that the altitude of the farm significantly affects many parameters, particularly those related to the rennet-coagulation: milk from higher farms over 3000 m a.s.l. has higher protein and casein content, and also higher paracasein content with respect to the milkproduced in farms under 3000 m. Compared with milk from other species, Qinghai plateau yak milk was very different from cow milk and more similar to ewe milk.