Effects of Dietary Astragalus Polysaccharides on Serum Biochemical Parameters, Intestinal Morphology, Organic Acid Profiles, and Cecal Microbiota in Taihu Geese

Astragalus polysaccharides (APS) have potential as functional feed additives, but their effects on physiological and intestinal responses in geese remain incompletely characterized. A total of 432 one-day-old Taihu goslings were assigned to diets containing 0, 100, or 200 mg/kg APS, with six replicates per treatment and 24 geese per replicate. Organ indices, serum biochemical and intestinal barrier-related parameters, and intestinal length were evaluated using six independent experimental replicates per treatment (n = 6), whereas intestinal histomorphology and cecal microbiota were assessed using four biological replicates per treatment (n = 4) at each sampling age. Samples were collected at 30, 60, and 90 d, with intestinal metabolites analyzed using four biological replicates per treatment (n = 4) and jejunal mucosal metabolic indicators evaluated using six experimental replicates per treatment (n = 6) at 90 d. Compared with the control, 200 mg/kg APS increased thymus index at 30 d, serum superoxide dismutase activity at 30 and 60 d (p = 0.038 and 0.020, respectively), and jejunal and ileal villus height at 30, 60, and 90 d. APS reduced serum diamine oxidase activity at 30 d (p = 0.001), and the 200 mg/kg group remained lower at 90 d. Cecal microbial community structure differed among treatments at 30 and 60 d (PERMANOVA p = 0.047 and 0.006, respectively), whereas Shannon diversity was unchanged. At 90 d, APS altered jejunal and cecal organic acid profiles with selected responses remaining significant after Benjamini–Hochberg false discovery rate correction (q < 0.05) and increased jejunal mucosal citric acid content at 200 mg/kg. APS affected selected physiological and intestinal outcomes, with additional changes in cecal microbial community structure and intestinal metabolism, while 200 mg/kg produced the clearest changes in serum superoxide dismutase activity and intestinal morphology.