Effects of dietary Astragalus polysaccharide and Astragalus membranaceus root supplementation on growth performance, rumen fermentation, immune responses, and antioxidant status of lambs

The aim of this study was to investigate effects of dietary Astragalus membranaceus root (AMT) and Astragalus polysaccharide (APS) supplementation on growth performance, blood metabolites, rumen fermentation, immune responses and antioxidant status of weaned lambs. Twenty-four male Ujumqin weaned lambs (a local breed) with average age of 60±10.3d and similar genetic background were randomly assigned to one of three treatments for a 30d feeding period. Treatments consisted of the lambs’ basal diets with addition of: (1) nothing (control), (2) 15g/kg APS or (3) 50g/kg AMT of the diet (dry matter (DM) basis). Blood samples were collected at day 0 and 30 and ruminal fluid samples at day 0, 15 and 30. Results showed that APS supplementation increased DM intake of lambs (P=0.003), but that average daily gain, feed efficiency and apparent digestibility of nutrients did not differ among treatments. Concentrations of ammonia N (P=0.004) and total volatile fatty acids (P=0.005) were affected by an interaction between treatment and feeding time. Both APS and AMT feeding increased propionic acid (P=0.025) which resulted in a reduction in the acetic acid to propionic acid ratios in ruminal fluid (P=0.014). Feeding APS and AMT increased total antioxidant capacity (P<0.001) and total superoxide dismutase activities (P<0.001), and decreased cortisol levels (P<0.001) in plasma. However, blood plasma metabolites such as blood urea N, high and low density lipoprotein–cholesterol, triglyceride, glucose and total protein, which are reflective of animal metabolism, were not affected by APS and AMT feeding. Only dietary AMT supplementation affected immune responses, including increased immunoglobulin M production (P<0.001) and lymphocyte numbers (P=0.024) in whole blood. Results suggest that APS and AMT feeding mainly improved antioxidant capacity and affected rumen fermentation patterns of lambs, while AMT supplementation affected immunity, but both additives failed to improve apparent digestibility of nutrients in weaned lambs.