Dietary Clostridium butyricum metabolites mitigated the disturbances in growth, immune response and gut health status of Ctenopharyngodon idella subjected to high cottonseed and rapeseed meal diet

Cottonseed meal and rapeseed meal exhibit a potential for fishmeal substitute in grass carp feed, while their excessive use contribute to growth decline and weakening immunity of aquatic animals. Clostridium butyricum metabolites (CBM) was recognized as a functional additive due to its antioxidant properties and maintenance of intestinal microbiota balance. CBM was added to a high of cottonseed and rapeseed meal diet to determine its effects on growth, immunity, and intestinal microbiota alterations of grass carp (Ctenopharyngodon idella) over 56 days. Eight hundred grass carp (mean weight, around 50 g) were randomized to five treatments and fed with the basic diet (CON), CBM0 diet (28 % cottonseed and 27 % rapeseed meal), and CBM diets (CBM0.5, CBM1, and CBM2, namely CBM0 diet supplemented with 500, 1000, and 2000 mg kg⁻¹ CBM). The results indicated that compared to CBM0, The ingestion of 1000 mg kg⁻¹ CBM diet by grass carp significantly promoted growth as measured by intestinal lipase activity, villus height, and muscle thickness. Moreover, accompanied by a decrease in intestine MDA content, and enhance antioxidant capacity by activating Keap1/Nrf2 signaling pathway to increase enzyme activities (SOD, CAT and T-AOC) and corresponding gene expression (mnsod, cat, gsto and gpx1) in the intestine of grass crap fed CBM1 diet. The dietary CBM1 diet increased serum levels of C3 and IgM, increased ACP activity and expression of the corresponding anti-inflammatory factors (tgf-β1 and il-15), and suppressed the expression of pro-inflammatory factors (tnf-α and il-12β), resulting in enhanced immunity. The dietary CBM1 diet up-regulates gene expression of tight junction proteins (zo-1, occludin, occludin7a and occludin-c), coupled with the decreases in DAO and D-lactate contents, implying that the decreased mucosal permeability could be observed in the gut. The dietary CBM1 diet largely altered the intestinal microbial community, especially reducing the relative abundance of intestinal pathogenic bacteria (Streptococcus and Actinomyces). And it significantly increased the content of short-chain fatty acids (acetic acid, butyric acid, isobutyric acid, propionic acid and isovaleric acid). Taken above, dietary CBM supplementation improved growth in grass carp and attenuated the intestinal oxidative stress, inflammation and microflora dysbacteriosis caused by high proportions of cottonseed and rapeseed meal diets.