Dietary astragalus stems polysaccharides improve antioxidant capacity and lactation performance in dairy goats through integrated metabolomic and mechanistic analyses

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.