Effects of protease-hydrolyzed cottonseed protein on growth performance, intestinal morphology, and bacterial diversity in broilers

The present study aimed to investigate the effects of enzymatically hydrolyzed cottonseed protein (EHCP) on growth performance, intestinal morphology, and bacterial diversity of broilers. A total of 480 one-day-old yellow-feathered broilers were randomly allocated into 5 groups with 8 replicates per group and 12 broilers per replicate, and the experimental period lasted for 63 days. The control group was fed a corn–soybean meal based basal diet. In the experimental groups, dietary protein from corn-soybean meal was partially replaced with EHCP at replacement levels of 25%, 50%, 75%, and 100%. During the period of 1–63 days of age, no significant differences were observed in body weight (BW), average daily gain (ADG), or feed conversion ratio (FCR) among all groups ( P > 0.05). Compared with the control group, the average daily feed intake (ADFI) in the 50%, 75%, and 100% substitution groups was significantly decreased ( P <0.05). At 63 days of age, compared with the control group, the digestibility of dry matter (DM), ether extract (EE), and organic matter (OM) was significantly decreased in the 25%, 50%, 75%, and 100% substitution groups; the crude protein (CP) digestibility in the 100% substitution group was significantly lower than that in all other treatment groups; and the gross energy (GE) digestibility in the 50% and 100% substitution groups was significantly lower than that in the control group ( P <0.05). No significant differences were observed in villus height, crypt depth, and villus height/crypt depth ratio (V/C ratio) in the duodenum, jejunum, and ileum among all groups (P > 0.05). 16S rDNA sequencing of cecal bacteria showed that compared with the control group, the Chao1, faith_pd, and observed-features indices in the 50%, 75%, and 100% substitution groups were significantly increased, and the Simpson index in the 25% and 75% substitution groups was significantly higher than that in the 100% substitution group ( P <0.05). Correlation analysis between differential cecal microbiota and volatile fatty acids (VFA) revealed that Mediterraneibacter was positively correlated with VFA, with a significant difference in relation to isobutyric acid, while Borkfalkia was negatively correlated with VFA, with a significant difference in relation to propionic acid ( P <0.05). In conclusion, the partial replacement of SBM with EHCP at an appropriate ratio in broiler diets had no adverse effects on broiler growth performance, intestinal morphology, or gut bacterial diversity. Considering the comprehensive indices of growth performance, nutrient metabolism and cecal microbial diversity, this study suggests that the maximum replacement level of EHCP should not exceed 75%.