Effects of dietary Astragalus Membranaceus supplementation on growth performance, and intestinal morphology, microbiota and metabolism in common carp (Cyprinus carpio)

A large number of studies have indicated that Astragalus Membranaceus (AM) possesses growth-promoting effects in animal husbandry. However, the function of AM in common carp growth performance has not meant fully evaluated. In this work, to investigate the potential effects of AM and Lactobacillus p/antarum-fermented AM (FAM) on growth performance, intestinal function, and intestinal microenvironment of common carp, fish with an average weight of 10.10 +/- 0.25 g were divided into seven groups, and fed daily with an additive-free basal diet (BD); 0.1%, 0.2%, and 0.4% (w/w) of AM (L-AM, M-AM, and H-AM); 0.1%, 0.2%, and 0.4% (w/w) of FAM (L-FAM, M-FAM and H-FAM) for an eight-week period. The results showed that incorporating L-AM or L-FAM in the diet significantly increased (P < 0.05) the final weight, weight gain ratio, and specific growth rate compared with the BD group, but significantly decreased (P < 0.05) the feed conversion ratio. In L-AM and L-FAM groups, the villus height was considerably increased (P < 0.05), and crypt depth remained unaffected. L-AM and L-FAM both changed the abundance of intestinal microbiota with strikingly different dominant microbiota. Dietary L-FAM supplementation increased the abundance of Firmicutes, Verrucomicrobia, Cyanobacteria, TM7, WS3, Chla-mydiae, TM6, Fusobacteria, Spirochaetes, Acidobacteria, Gemmatimonadetes, Actinobacteria, Chloroflexi, [Thermi], and Nitrospirae, whereas decreased Bacteroidetes and Proteobacteria abundances. Intestinal metabolome analyses demonstrated that L-AM altered metabolic composition and function, which were linked to immunity and host metabolism. Furthermore, L-FAM showed superior beneficial metabolic effects than L-AM in fish. On growth performance improvement and intestinal microenvironment modulation, dietary L-FAM supplementation was superior to AM in common carp. We speculate that L-FAM may improve the intestinal morphology and microenvironment, which strengthens the growth of fish. In addition, FAM might be promising antibiotics' alternatives for promoting fish growth and controlling pathogens that has immense economic value in aquaculture.