Effects of Astragalus membranaceus roots supplementation on growth performance, serum antioxidant and immune response in finishing lambs.

Astragalus membranaceus root is a well-known traditional Chinese herbal medicine with many biological active constituents. This study was conducted to examine the effects of Astragalus membranaceus root powder (AMP) on growth performance, serum antioxidant and immune response in finishing lambs.A total of thirty-six Guangling fat-tailed ram lambs (BW=19 ± 2 kg, mean ± SD) were randomly assigned to one of six treatments for a 40 d feeding period, with the first 10 d for adaptation. Treatments consisted of the lambs' basal diets with addition of 0, 5, 10, 15, 20, and 30 g/kg of diet of AMP.Response to supplementation level of AMP was quadratic (p ≤ 0.032) for final weight and ADG with the greatest at 10 g/kg of diet, but DMI was not affected (p ≥ 0.227) by treatments. The increase of AMP supplementation resulted in a quadratic response in contents of triglyceride (TG) and creatinine (p < 0.05), with the lowest values for 10 and 20 g/kg of diet, respectively. A linear and quadratic decrease was observed in activity of alkaline phosphatase (ALP) in serum of lambs. As the AMP supplementation increased, the activities of total superoxide dismutase (T-SOD) and total antioxidant capacity (TAC) increased linearly (p ≤ 0.018) and hydroxyl radical (OH-) decreased linearly (p = 0.002). For catalase (CAT) and malondialdehyde (MDA), quadratic (p ≤ 0.001) effects were observed among treatments, with the greatest CAT and lowest MDA values at 10 g/kg AMP. Additionally, supplementing AMP up to a level of 10 or 15 g/kg of diet quadratically increased immunoglobulin and interleukin contents in the serum.The results indicated that AMP can be used as natural feed additive in the ration of lambs to improve ADG, antioxidant status, and immune functions, and the optimal dose was 10 g/kg of diet under the condition of this experiment.