Dietary antimicrobial peptides are associated with improved colonic immunity and barrier function and altered microbiota–metabolite profiles in fattening Holstein bulls

Background Feeding high-concentrate diets induces gastrointestinal mucosal damage, hindgut acidosis, and intestinal inflammation in ruminants, severely compromising their health status. Antimicrobial peptides (AMP) have gained significant attention as a promising alternative to antibiotic feed additives, owing to their broad-spectrum antimicrobial activities and beneficial biological functions. Therefore, to alleviate the issues arising from high-concentrate diets and those owing to excessive use of antibiotics, 18 Holstein bulls were selected in this study for a fattening trial. They were randomly allocated into control (CON, fed a basal diet) and AMP (basal diet supplemented with 8 g·d ^− 1 ·head ^− 1 AMP) groups. After a 270-day experimental period, colon health was systematically evaluated. Results Multi-omic integration (microbiome, metabolome, and transcriptome) and phenotypic analyses revealed that AMP intervention significantly reshaped the colonic microbial structure, increasing the abundance of Firmicutes-affiliated genera, such as Negativibacillus , Christensenellaceae_R-7_group , and Lachnospiraceae_UCG-010 , while enhancing the production of microbial metabolites, particularly propionate, butyrate, 3-aminobenzamide, hispidol, and N-acetyl-5-hydroxytryptamine. These changes collectively strengthened colonic barrier function, as evidenced by significantly upregulated gene expression of tight junction proteins ( ZO-1 , claudin-1 , and claudin-4 ) and mucins ( MUC1 and MUC2 ). Concurrently, the AMP group exhibited reduced the expression of proinflammatory cytokine genes ( TNF-α , IL-1β , and IL-6 ) and elevated the levels of the anti-inflammatory cytokine gene IL-10 , upregulation of PIGR , and significantly increased concentrations of secretory immunoglobulin (sIg) A and sIgM, indicating enhanced mucosal immunity. Conclusion Dietary supplementation with AMP was associated with improved colonic health in finishing Holstein bulls, accompanied by reduced intestinal damage, attenuated inflammation, and changes in colonic barrier function and gut microbiota–metabolite profiles.