Caragana korshinskii tannin improves colonic barrier function through promoting the production of taurocholic acid by Alistipes onderdonkii in high concentrate fed lambs

Background High-concentrate diets can impair colonic barrier function in lambs. Although tannins are considered promising regulators of intestinal health, their protective effects and underlying mechanisms in high-concentrate-induced intestinal injury remain unclear. Results We first demonstrated that long-term feeding of a high-concentrate diet impairs the colonic barrier function in lambs, whereas dietary supplementation with Caragana korshinskii tannin (CKT) markedly alleviated this impairment. Specifically, CKT improved colonic morphology, increased expression of tight junction proteins in the intestinal mucosa, and enhanced immune and antioxidant capacities. We then showed, through 16S rRNA gene amplicon sequencing and metagenomic analysis, that CKT modulated the colonic microbiota structure and function, altered microbial interactions, and promoted the enrichment of Alistipes onderdonkii . Untargeted metabolomics further revealed increased abundances of cholic acid, taurocholic acid, and chenodeoxycholic acid in the colonic digesta of CKT-treated lambs, among which taurocholic acid was positively correlated with Alistipes onderdonkii . Then, we verified in vitro that Alistipes onderdonkii can utilize CKT for growth and taurocholic acid production. Colonic transcriptomic analysis revealed that the PPAR signaling pathway was significantly enriched in CKT group, and taurocholic acid was positively correlated with key genes of this pathway ( FABP, PPARα, SCD ). In ovine colonic mucosal epithelial cells, taurocholic acid upregulated the expression of PPAR pathway-related genes and tight junction proteins. We also verified that both TCA and Alistipes onderdonkii interventions alleviated colonic inflammation, reduced intestinal permeability, and activated PPAR signaling in a DSS-induced mouse colitis model. Conclusions This study demonstrates that dietary CKT ameliorates high-concentrate-induced colonic barrier dysfunction in lambs by enriching Alistipes onderdonkii and promoting its synthesis of taurocholic acid, which in turn activates the PPAR signaling pathway to enhance intestinal barrier integrity. These findings provide novel mechanistic insights into CKT-mediated protection against intestinal injury and highlight CKT as a promising dietary supplement for maintaining gut health in intensively reared lambs.