Exploring the effects of astragalus polysaccharide food supplementation on growth performance, immunity, antioxidant capacity, and intestinal microflora in Chinese mitten crabs

Astragalus polysaccharide (APS) is the main active ingredient in astragalus membranaceus, which is composed of rhamnose, arabinose, xylose, mannose, galactose, and glucose. This research evaluated dietary addition with APS effects on growth, non-specific immune, antioxidant status and intestinal microbiota of Chinese mitten crabs. Altogether 288 crabs with intact appendages were irregularly assigned 12 crabs per replicate to 24 tanks with 6 replicates per treatment. Crabs were given a basal diet in different groups containing 0 (control group), 500, 1000, and 2000 mg/kg of APS, respectively. The results indicated that the dietary APS addition increased the specific growth rate and percentage weight gain, serum phenoloxidase and lysozyme activities, increased superoxide dismutase and glutathione peroxidase activities of serum and hepatopancreas, reduced the feed conversion ratio of Chinese mitten crabs (P < 0.05). APS addition quadratically increased acid phosphatase levels, decreased the malondialdehyde levels of Chinese mitten crabs (P < 0.05). APS inclusion linearly and quadratically increased hepatopancreas mRNA expression levels of TLR2, MyD88 and Tube of crabs (P < 0.05). Principal component analysis showed that the four groups had different composition of the intestinal microbiota in Chinese mitten crabs. On the other hand, this addition decreased the Chao1, Shannon indexes, abundance of phyla Bacteroidota, increased the abundance of phyla Firmicutes and genus Candidatus_Bacilloplasma in intestine microbiota of Chinese mitten crabs compared with the control (P < 0.05). The level of APS to the diet of Chinese mitten crabs with a 1000 mg/kg inclusion was better compared to its counterparts with 500 and 2000 mg/kg inclusions according to the better results on growth, immunity, and antioxidant capacity. In summary, dietary APS inclusion enhanced growth performance via improving antioxidant function, non-specific immunity, modulating the Toll/NF-κB pathway and proPO system, and ameliorating the intestinal flora in Chinese mitten crabs. The optimal level of supplemented APS in the diet was 1000 mg/kg.