Abstract: 【Objective】 The influences of different weaning strategies on growth, serum biochemical indexes and antioxidant capacity of yak calves were investigated in the present study, with the purpose of exploring scientific early fostering pattern in yak calves.【Method】 24 healthy newborn yak calves with similar body weight were selected and randomly divided into 3 treatment groups.8 calves (half males and half females) were assigned to each group.The calves in control group (GF) were breastfed with dam on grazing pasture, while the calves in early weaning group (EW) were breastfed for 15 days after birth and then separated from the dam.These calves were sebsequently fed with milk replacer by gradual transition, and starter concentrate and natural grass were provided for ad libitum intake.Milk replacer feeding was stopped when the starter concentrate intake of calves reached 0.5 kg/d.At 90 days of age, the calves were switched to grazing feeding on natural grassland without concentrate.Calves in early weaning with probiotics group (EWP) followed the same weaning protocol as EW group, and probiotics compound (Lactobacillus, Bacillus and yeast, ≥ 9.98×10¹¹ CFU/g) was supplemented into the milk replacer and starter concentrate.The body weight and size indexes were measured at 30, 60, 90 and 150 days of age.Blood samples were collected from jugular vein of calves before morning feeding at 30, 60 and 90 days of age.Serum samples were separated for the analysis of metabolites, hormones, immunoglobulins and antioxidant capacity.【Result】 At 30 days of age, the body weight, body size, serum glucose (GLU), triglycerides (TG), cholesterol (CHO), growth hormone (GH), insulin-like growth factor 1 (IGF-1), and immunoglobulin A, G (IgA, IgG) concentrations of calves in EW and EWP groups were significantly lower than those in GF group (P<0.05), and the cortisol level of EW group was significantly higher than that of GF group(P<0.05).There was no significant difference in body weight and body size among treatments from 60 to 150 days of age (P>0.05).At 60 days of age, the serum IGF-1, glutathione peroxidase (GSH) levels were significantly increased in EW and EWP groups compared to GF group (P<0.05).At 90 days of age, the serum GLU, blood urea nitrogen (BUN), IGF-1, thyroxine (T₄) and IgA concentrations of calves in EW and EWP groups were significantly greater than those in GF group (P<0.05).Moreover, calves in EWP group had significantly higher TG, GH concentrations and catalase (CAT) enzyme activity compared to GF group (P<0.05).【Conclusion】 In comparison with the breastfeeding model with grazing dam, both of the two early weaning strategies had a negative impact on yak calf in the early stage (30 days of age).However, the supplementations of milk replacer and starter concentrate after early weaning (60-90 days of age)were beneficial to improve the later growth, nutritional metabolism, immunity and antioxidant capacity of calves.Besides the beneficial effect of early weaning strategy, probiotics supplementation in early weaning further relieved the weaning stress, and promoted the growth and antioxidant capacity of yak calves.

Key words: yak calf; weaning strategy; growth and development; serum biochemical indexes; antioxidant capacity