Physiological and Biochemical Characteristics of Lactation in Half-lactating Yak

Yaks of two lactating types, the half-Iactating yak and the total lactating yak, were investigated in their milk compositions, milk coagulation properties, and contents of three kinds of hormones, glucose, and protein in plasma. The half-lactating Maiwa yak and Jiulong yak contained significantly higher contents of protein, fat, and activities of alkaline phosphatase and Y-glutamyl transpeptidase in milk than that of the corresponding total-lactating yak breeds, with reduced milk yield and similar lactose level and relative percentages of main milk protein components. The half-lactatin yak resembled yaks in a late stage of lactation in their biochemical composition of milk; however, significant differences were also observed, which indicated that the former was in a special stage of lactation quite different from dairy cows. Milk of the total-lactating or half-lactating yaks could be coagulated normally by adding chymosin, with a similar coagulation time. No significant difference was observed between p