Effects of high-concentrate feeding and yeast culture supplementation on cecal fermentation, microbiota, metabolite profiles, and mucosal responses in lambs

Objective: Although yeast culture (YC) has been widely studied for its beneficial effects on ruminal fermentation, its effects on cecal microbial, metabolic, and mucosal responses under high-concentrate feeding remain unclear.This study evaluated cecal fermentation, microbial, metabolic, and mucosal responses to high-concentrate feeding and YC supplementation in lambs.Methods: Forty-five three-month-old Du × Han F1 male lambs were assigned to three A c c e p t e d A r t i c l edietary treatments for 60 days: a control diet with a concentrate-to-roughage ratio of 1.3:1 (CON), a high-concentrate diet with a ratio of 1.7:1 (HC), or the HC diet supplemented with 0.5% YC.At the end of the trial, six lambs from each treatment were selected for terminal sampling.Cecal fermentation, mucosal histology, 16S rRNA gene sequencing, untargeted metabolomics, and quantitative real-time PCR were evaluated.Results: Compared with the CON group, HC feeding decreased cecal pH, acetate, isovalerate, valerate, and the acetate-to-propionate ratio and was accompanied by mucosal injury, lower expression of tight junction-related genes, and higher expression of inflammatory cytokines.Alpha diversity did not differ among treatments, whereas overall microbial community structure and cecal metabolic profiles varied among groups.YC supplementation increased cecal pH and improved selected fermentation indices, particularly valerate concentration and the acetate-to-propionate ratio.It also ameliorated mucosal lesions, increased the expression of ZO-1, Occludin, Claudin-1, and Claudin-4, and decreased TNF-α and IL-1β expression.Candidate differential metabolites identified between the YC and HC groups were associated with pathways including cholesterol metabolism, primary bile acid biosynthesis, bile secretion, ABC transporters, and AMPK signaling.Exploratory correlation analysis identified nominal associations between selected bacterial genera and candidate differential metabolites related to lipid, organic acid, and bile acid metabolism.Conclusion: YC supplementation partially alleviated high-concentrate diet-associated alterations in cecal fermentation and mucosal injury, accompanied by changes in barrier-related gene expression, cecal microbiota, and metabolite profiles.