Astragalus root extract improved average daily gain, immunity, antioxidant status and ruminal microbiota of early weaned yak calves

BACKGROUND: Early weaning in yak calves is being attempted to improve yak reproduction rate. However, this has to be done with caution because of the high mortality rate of calves due to the lack of nutrients and the harsh environmental conditions. Twenty-four weaned male yak calves were used in a 60 day feeding trial in which astragalus root extract (ARE) was supplemented. They were assigned randomly to one of four dietary treatments (n = six per treatment) that differed in ARE level: 0 g kg⁻¹ (control), ARE₀; 20 g kg⁻¹, ARE₂₀; 50 g kg⁻¹, ARE_50; and 80 g kg⁻¹ dry matter intake (DMI), ARE₈₀. RESULTS: Final bodyweight and average daily gain (ADG) were significantly higher and the DMI/ADG ratio was significantly lower in calves with ARE supplementation than control (ARE₀) calves. Ruminal concentrations of acetate and propionate and serum concentration of superoxide dismutase in ARE₈₀ calves were higher than in the other groups and serum concentration of insulin was higher in ARE₈₀ calves than in ARE₂₀ calves. Serum immunoglobulin G (IgG) and interleukin-2 (IL-2) concentrations in ARE-fed calves were higher than in controls. Serum tumor necrosis factor (TNF-α) concentration was higher in ARE₅₀ and ARE₈₀ groups than ARE₀ calves and serum interleukin-6 (IL-6) concentration was higher in ARE₈₀ than in ARE₀ calves. Serum immunoglobulin A (IgA), IgG and immunoglobulin M (IgM) concentrations increased with age in ARE-fed calves. ARE supplementation increased the abundance of fiber degrading bacteria. CONCLUSION: ARE at a dosage of 5% to 8% DMI can be supplemented to early weaned yak calves to improve growth performance, antioxidant capacity and immunity.