Compound probiotics alleviate Escherichia coli-induced diarrhea in calves by modulating tryptophan and bile acid metabolism of the fecal microbiota

Calf diarrhea, particularly that caused by diarrheagenic Escherichia coli, has become a major issue affecting the sustainable development of the calf farming industry. Although the use of traditional antimicrobial agents can alleviate symptoms, challenges such as antibiotic resistance, drug residues, and intestinal microbiota dysbiosis urgently need to be addressed. Therefore, this study investigates the mechanism by which compound probiotics alleviate diarrheagenic Escherichia coli-induced diarrhea in calves. Compound probiotics were administered to calves with diarrheagenic Escherichia coli-induced diarrhea, and their effects on growth performance, intestinal microbiota structure, and metabolic profiles were evaluated. The results showed that compound probiotic intervention significantly improved calf growth performance and weight gain. Integrated 16S rRNA sequencing and metabolomics analyses revealed that compound probiotic intervention markedly modulated the intestinal microbiota, particularly by increasing the abundance of the genus Blautia, while also improving tryptophan and bile acid metabolic pathways. Furthermore, fecal microbiota transplantation experiments conducted in both calves and antibiotic-induced microbiota depletion mouse models confirmed the regulatory effects of compound probiotics on the intestinal microbiota, especially with respect to tryptophan and bile acid metabolism. Compound probiotic intervention regulated key metabolites, including kynurenic acid, taurodeoxycholic acid, and ursodeoxycholic acid, which were positively correlated with Blautia, and significantly reduced inflammation by downregulating pro-inflammatory factors and upregulating anti-inflammatory factors, thereby alleviating diarrheagenic Escherichia coli-induced diarrhea in calves. Overall, this study provides new insights into the application of probiotics in intestinal health management and highlights the significant potential of compound probiotics as an alternative to antibiotics for the treatment of calf diarrhea.