Abstract: On the basis of feeding situation of dam and calf in yak industry, this study was conducted to investigate the effects of maternal nutritional supplementation in transition period and early weaning on the growth, serum biochemistry and immune function of yak calves, with the purpose of providing scientific basis for the efficient feeding of yaks. In this study, 18 healthy yaks in late gestation with similar body weight, day of pregnancy and 2-4 parities were randomly divided into 3 groups, including grazing feeding group (GF, n=6), nutritional supplementation group (SF, n=6) and nutritional supplementation and early weaning group (SW, n=6). Yaks in GF group were grazing feeding on the natural pasture throughout the transition period. The SF group were given a balanced nutritional supplementation with concentrate, hay and grazing feeding from 30 days before to 90 days after parturition according to the nutrition requirement of late pregnancy and early lactation, while yaks in the SW group were early weaned at 60 d after parturition besides balanced nutritional supplementation. The body weight and measurement of calves at birth and 90 d in GF, SF and SW groups were measured. Serum samples were collected at the age of 90 d to analyze the differences on serum biochemistry, growth related hormone secretion and immune function of yak calves with different maternal nutritional regulation. The results showed that the birth weights of calves in the SF and SW groups were significantly increased when compared to those in the GF group (P < 0.05). At 90 d of age, body weight, height and chest circumference of calves in the SF and SW groups were significantly higher than those in the GF group (P < 0.05), and there was no significant differences in calf weights and body measurements between SW and SF groups (P>0.05). Compared with the GF group, the serum glucose (GLU), globulin (GLB), and cholesterol (CHO) concentrations of calves in the SF and SW groups were significantly increased (P < 0.05), and calves in the SF group had significantly higher serum TP levels than those in the GF group (P < 0.05). For growth-related hormones, insulin-like growth factor I (IGF-Ⅰ) concentrations were significantly improved by the SF and SW treatment (P < 0.05). Serum growth hormone (GH) level in the SW group were significantly higher than that in the GF group (P < 0.05). Regarding to immune function, the serum secretory immunoglobulin A (sIgA) concentration of SF and GF groups was significantly higher than that in SW group (P < 0.05). In comparison with the GF group, the serum immunoglobulin A (IgA) level was significantly increased in the SF and SW groups (P < 0.05), and the serum immunoglobulin G (IgG) concentration was significantly higher in the SF group than in the GF group (P < 0.05). In conclusion, the nutritional supplementation in transition period provided sufficient nutrients to yak dam in late pregnancy and early-lactation, increased nutrient intake of yak calf thus enhanced the birth weight, serum glucose and nitrogen metabolite concentrations, and increased the secretion of growth-related hormone and immunoglobulin, as a consequence of that, the growth of yak calf was promoted. Meanwhile, early weaning with nutritional supplementation had no obvious negative effect on calf growth and immune function, and the secretion of growth hormone was further improved.

Key words: transition period, nutritional regulation, early weaning, calf yak, growth and development