Abstract
Astragalus stems are abundant yet underutilized in livestock feeds. This study optimized the extraction of Astragalus stem polysaccharides (ASPS) and assessed their efficacy as a natural antioxidant in improving milk yield and metabolic profiles in dairy goats. Hot-water extraction was optimized (solid-to-liquid ratio of 1: 30, 2 h duration, 85 °C) to achieve a polysaccharide yield of 119.38 ± 4.27 mg/g. Mid-lactation dairy goats supplemented with ASPS [100 mg/kg dry matter (DM) daily] showed increased milk yield and milk protein content, along with reduced blood urea nitrogen (BUN), alkaline phosphatase (ALP), and malondialdehyde (MDA) levels. Supplementation also elevated immunoglobulin A (IgA), total antioxidant capacity (T-AOC) and catalase (CAT). Serum metabolomics identified 307 differentially expressed metabolites (DEMs) enriched in glycerophospholipid metabolism and D‑amino acid metabolism. Six key metabolites were selected for molecular docking against relevant targets; all bound with affinities ≤ - 5.0 kcal/mol, with phenylacetyl‑L‑glutamine-D-amino acid oxidase (DAO) showing strongest affinity (- 8.34 kcal/mol). Molecular dynamics simulation suggested stable binding of phenylacetyl-L-glutamine to DAO, with MM-PBSA estimating a favorable free energy (- 92.051 ± 0.366 kJ/mol) dominated by van der Waals interactions. This findings provide valuable insights into the utilization of AS as well as its application in enhancing productivity within the dairy goat industry.