This study was designed to evaluate the effects of γ-irradiated Astragalus polysaccharides ( IAPS ) on growth performance, cecal microbiota populations, and concentrations of cecal short-chain fatty acids of immunosuppressed broilers. A total of 144 one-day-old broiler chicks were randomly assigned into 3 groups: nontreated group (control), cyclophosphamide ( CPM )-treated groups fed either a basal diet or the diets containing 900 mg/kg IAPS, respectively. On day 16, 18, and 20, broilers in the control group were intramuscularly injected with 0.5 mL sterilized saline (0.75%, wt/vol), and those in the CPM and IAPS groups were intramuscularly injected with 0.5 mL CPM (40 mg/kg of BW). The trial lasted 21 d. Compared with the control group, CPM treatment decreased the broiler average daily gain ( ADG ) and feed intake ( P < 0.05) but did not affect the overall microbial diversity and compositions, as well as the concentrations of cecal acetate, propionate, and butyrate in cecum of broilers ( P > 0.05). Dietary IAPS supplementation increased broiler ADG, Shannon index, and decreased Simpson index ( P < 0.05). Specifically, broilers fed diets containing IAPS showed lower abundances of Faecalibacterium , Bacteroides, and Butyricicoccus and higher proportions of Ruminococcaceae UCG-014 , Negativibacillus , Shuttleworthia , Sellimonas, and Mollicutes RF39_norank, respectively ( P < 0.05). The IAPS treatment also increased butyrate concentration ( P < 0.05) and tended to elevate acetate concentration ( P = 0.052) in cecal digesta. The results indicated that IAPS are effective in increasing the cecal beneficial bacteria and short-chain fatty acids production, contributing to improvement in the growth performance of immunosuppressive broilers. These findings may expand our knowledge about the function of modified Astragalus polysaccharides in broiler chickens.

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