Replacement of soybean meal with water-soluble corn protein improves early growth performance of broilers via regulating intestinal microbiota and metabolites.

This study aimed to investigate the effects of 5% dietary replacement of soybean meal (SBM) with water-soluble corn protein (WCP) or cottonseed protein (CotP) on growth performance and intestinal development of starter broilers, with the underlying microbial and metabolic mechanisms of WCP further explored. A total of 504 one-day-old male Arbor Acres broilers were randomly assigned to three isonitrogenous and isocaloric dietary treatments: a basal diet control group (CON), a WCP group (5% of SBM replaced by WCP), and a CotP group (5% of SBM replaced by CotP). The results showed that WCP significantly increased the 14-day body weight, average daily gain and average daily feed intake of broilers, improved duodenal villus morphology, and lowered duodenal digesta pH (P < 0.05) without damaging intestinal barrier function. In contrast, CotP inhibited early growth and reduced duodenal goblet cell density (P < 0.05). Further cecal microbial and metabolomic analyses were performed between the CON and WCP groups. Although WCP did not affect the alpha diversity of cecal microbiota, it substantially altered microbial community structure, increased the relative abundances of beneficial Clostridium, Romboutsia and Anaerofilum, and decreased Anaerobutyricum (P < 0.05). Metabolomic profiling revealed significant differences in cecal metabolites, and protein digestion and absorption was identified as the key enriched pathway. WCP supplementation upregulated isovaleric acid accumulation and decreased the level of harmful indole metabolites. Spearman correlation analysis showed that Clostridium and Romboutsia were positively correlated with body weight, while Anaerofilum was positively correlated with average daily feed intake. Moreover, isovaleric acid was positively associated with Clostridium and Anaerofilum, and exhibited highly significant positive correlations with duodenal villus height, body weight and average daily gain. Collectively, WCP specifically promotes early broiler growth by modulating cecal microbial structure and improving protein fermentation metabolism, suggesting its potential as a high-quality alternative protein source for starter broiler diets.