Effects of Astragalus membranaceus stems and leaves on broiler growth, antioxidant and immune status: Associating gut microbiota and serum metabolome

Astragalus membranaceus stems and leaves (AMSL), the aerial parts of the plant Astragalus membranaceus , are produced in large quantities annually but remain underutilized. AMSL contain active components such as flavonoids, saponins, and polysaccharides, as well as nutrients such as amino acids and minerals, indicating potential applications in animal husbandry. However, it remains unclear whether AMSL supplementation in animal feed is accompanied by alterations in endogenous metabolites and the gut microbiota. In this study, broilers were fed a basal diet supplemented with varying concentrations of AMSL (0%, 1%, 3%, and 5%) to evaluate the effects of AMSL on growth performance, antioxidant capacity, immune status, the gut microbiota, and serum metabolomics of broilers. The results showed that moderate AMSL supplementation (1–3%) did not negatively affect broiler growth performance, whereas excessive AMSL (5%) reduced production efficiency. Additionally, AMSL promoted the development of the spleen, increased total serum protein levels, and decreased serum aspartate aminotransferase level. Appropriate AMSL supplementation increased serum antioxidant activity and immune capacity, particularly at concentrations ranging from 3–5%. Further analysis of the intestinal microbiota revealed that 3% AMSL significantly modulated the composition of the cecal microbiota by promoting the growth and enrichment of Lactobacillus while inhibiting Pseudomonas, Ruminococcus , and Bacteroides . Moreover, 3% AMSL regulated serum endogenous metabolite levels by influencing purine, amino acid, and lipid metabolisms. This study confirms the potential of using AMSL in broiler farming, and provides a scientific basis for their use as a functional feed or feed additive in the poultry industry, promoting the intensive development and value-added utilization of AMSL.