[Effects of soybean fermented bioactive peptides on intestinal health of bullfrogs]

To address the challenges of antibiotic overuse and high feed costs in bullfrog aquaculture, this study aimed to systematically evaluate the effects of soybean fermented bioactive peptides (SFP) as a functional feed additive on the growth performance and intestinal health of bullfrogs (Lithobates catesbeianus). A total of 450 healthy bullfrogs with an initial body weight of (100.0±2.0) g were randomly assigned into three groups: group C (basal diet), the 2% SFP group (basal diet supplemented with 2% SFP), and the 3% SFP group (basal diet supplemented with 3% SFP). The feeding trial lasted for 6 weeks. After the experiment, growth performance, intestinal morphology, digestive enzyme activities, relative mRNA expression levels of inflammatory cytokines, and expression levels of the tight junction protein ZO-1 were systematically measured. Additionally, the intestinal microbiota structure was analyzed using 16S rRNA gene high-throughput sequencing, and the content of short-chain fatty acids (SCFAs) in the intestine was determined by gas chromatography-mass spectrometry (GC-MS). The results showed that compared with the control group, dietary SFP supplementation significantly promoted bullfrog growth and improved intestinal health. Among the treatments, the 2% SFP group exhibited the most prominent effects, with significantly higher weight gain rate and specific growth rate than those in the control group and the 3% SFP group (P0.05). The 2% SFP supplementation also significantly increased the villus height in the jejunum and ileum (P0.05), enhanced intestinal digestive enzyme activities, remarkably downregulated the mRNA expression levels of intestinal pro-inflammatory cytokines (P0.05), and upregulated the expression of the tight junction protein ZO-1. Further analysis of the intestinal microbiota revealed that 2% SFP optimized the microbial community structure by increasing the relative abundance of beneficial bacteria such as Clostridium and Lactococcus. Although the 3% SFP group exhibited an increased relative abundance of Bacteroides, its modulatory effect on the intestinal microbiota structure was inferior to that of the 2% SFP group. Consequently, the intestinal content of acetic acid and n-butyric acid was significantly higher in the 2% SFP group than in the 3% SFP group (P0.05). Therefore, these findings demonstrate that dietary supplementation with 2% SFP enhances the growth performance and intestinal health of bullfrogs by optimizing the intestinal microbiota composition, strengthening intestinal metabolic capacity, improving intestinal barrier integrity, and facilitating better digestion and absorption. This study establishes an effective feeding strategy for feed additives to promote healthy bullfrog cultivation, thereby facilitating the green and sustainable development of the bullfrog aquaculture industry.