Effects of dietary supplementation with astragalus polysaccharides on growth performance, serum parameters, and rumen microbial function of yaks

Astragalus polysaccharide (APS) has become a natural feed additive that has attracted much attention in animal husbandry due to its significant immunomodulatory activity, low toxicity and promotion of animal growth performance. In this study, in order to explore the effects of dietary APS on the growth performance and rumen microorganisms of yaks, 20 male yaks aged 2–3 years were selected and randomly divided into two groups: experimental group (1.0 g/kg APS were added to the diet, AG) and control group (no APS were added to the diet, CG), with 10 yaks in each group. After 60 days of continuous feeding, 5 animals were randomly selected from each group to collect rumen fluid. Comparative analysis of rumen microbial composition, function, and metabolites was conducted using metagenomic and metabolomic approaches. The analysis of yak body weight index showed that the body weight of yak in the AG group was significantly higher than that in the CG group on the 60 th day (P < 0.05). In addition, APS significantly increased the immune indexes of IgA, IgM, IgG, IL-10, IGF1, GH, and NOS in yaks (P < 0.05). Metagenomic analysis showed that the beneficial bacteria (such as Euryarchaeota, Methanobrevibacter and Butyrivibrio) in the rumen of yaks were significantly increased after the addition of astragalus polysaccharides in the experimental group. Differential metabolites were significantly enriched in pathways such as Purine metabolism, Galactose metabolism and Tryptophan metabolism that may have a positive impact on the growth and development of yaks. This may promote the production of immune and growth-related metabolites by regulation, and ultimately enhance the immune function and growth performance of yak. The results showed that the addition of APS could significantly improve the growth performance and immune function of yak. It can also optimize the rumen microbial community. It shows that polysaccharides such as APS can be used as effective substitutes for antibiotics and other drugs for long-term improvement of yak growth performance and rumen health.