Feasibility evaluation of cottonseed protein concentrate to replace soybean meal in the diet of juvenile grass carp (Ctenopharyngodon idellus): Growth performance, antioxidant capacity, intestinal health and microflora composition

An investigation into the replacement of soybean meal (SBM) with cottonseed protein concentrate (CPC) in the diet of grass carp feed (Ctenopharyngodon idellus) was carried out. During a 56-day feeding trial, 750 grass carp were fed five experimental diets (isonitrogenous and isolipidic) with different levels of CPC: SBM (control group), CPC25, CPC50, CPC75, and CPC100, corresponding to dietary SBM replacements levels of 0%, 25%, 50%, 75%, and 100%. The results showed that dietary CPC inclusion significantly increased FW, WGR, and PER (P < 0.05) except CPC100 groups, which did not differ with SBM group (P > 0.05). FCR was remarkably increased when SBM replacement levels reached up to 100% (P < 0.05). Based on broken-line regression analysis of WGR against the dietary replacement of SBM with CPC, the optimal replacement level of SBM with CPC was estimated to be 75.11% for juvenile grass carp. Muscle texture parameters hardness, gumminess and chewiness were apparently elevated (P < 0.05), demonstrated an improved flesh quality followed CPC added. The CPC inclusion groups showed significantly higher serum IgM, C3 amd C4 contents, as well as ACP and AKP activities than SBM group except CPC100 groups (P < 0.05). The hepatic antioxidant capacity was enhanced followed CPC inclusion verified at enzymatic and transcriptional levels (P < 0.05). The intestinal inflammation was relieved evidenced by the down-regulated il-β, il-6 and tnf-α expressive abundance mediated through NF-κB pathway (P < 0.05). Additionally, the intestinal mucosal barrier function was enhanced by the up-regulation of tight junction proteins (occludin, claudin12, zo-1, and zo-2). The intestinal lipase and trypsin activities in CPC50 and CPC75 and intestinal folds height in CPC25, CPC50 and CPC75 were advanced (P < 0.05). The gut microbiota revealed no significant differences in the alpha diversity indices across treatments (P > 0.05). While the key bacteria of Aeromonas in the CPC100 group was increased leading intestinal dysbacteriosis. Besides, the ME1 of the microbial network has a negative correlation with pro-inflammatory gens and a positive correlation with antioxidant gens and tight linking proteins (P < 0.05). Summarily, CPC could partially replace SBM with positive influences on growth, antioxidant capacity, immunity, and intestinal microbiota in grass carp.