Soybean meal-refined treatment mitigated high soybean meal diet-induced oxidative damage in the gut of crayfish via microbial metabolic function remodeling

The high cost and unreliable supply of fishmeal has stimulated concern over low fishmeal feed, making soy-derived protein receive more attention recently. However, dietary supplementation with high soybean meal (SBM) negatively affects host growth, health status, and gut microbial metabolic functions, encouraging the search for novel soy-derived protein sources to replace SBM. Accordingly, this experiment was designed to investigate the effects of replacing SBM with fermented soybean meal and soy protein concentrate on the growth, gut histomorphology, antioxidant capacities, and non-specific immunity of crayfish, together with the underlying metabolic mechanisms of microbial regulation. 600 crayfish (4.00 g) were randomized into four treatments (FM, SBM, FSM, and SPC) and fed diets with fishmeal and three different soy-derived proteins for six weeks. The present findings revealed that dietary FSM and SPC inclusion mitigated the growth decline and intestine injury caused by the SBM diet, as evidenced by the well-developed villus, epithelium, and dense connective tissue, as well as lower hemolymph malondialdehyde and lactic acid contents (P < 0.05). Moreover, crayfish supplemented with FSM and SPC diets experienced enhanced immunity compared to the SBM group, together with the increased hemolymph lysozyme and acid phosphatase levels (P < 0.05), and the decreased nfkb and alf mRNA expression levels (P < 0.05). Also, crayfish given FSM and SPC diets exhibited increases in the intestine glutathione content and nrf2 mRNA expression level (P < 0.05). Furthermore, dietary FSM and SPC supplementation eliminated SBM-induced microbial dysbiosis and dysfunction, characterized by the decreased Citrobacter and Anaerorhabdus and increased RsaHf231. Further findings revealed that the identified 88 differential microbes and 66 differential metabolites were shared between the SBM group and the FM and SBM-refined groups, with Candidatus Bacilloplasma, Cyanobium PCC-6307, and Vogesella, and phosphatidylcholine being the main contributors to crayfish health. Moreover, dietary SBM-refined treatment contributed to more robust and complicated microbial co-occurrence networks and activated amino acid metabolism-related pathways. To conclude, dietary FSM and SPC supplementation reversed the weakened immunity and antioxidant capacities of crayfish given a soybean meal diet by reshaping microbial metabolic functions, which in turn improved the growth and gut histomorphological structure.