Effects of Compound Yeast Culture and Yeast Cell Wall Polysaccharide on Intestinal Barrier Function in Mongolian Ram Lambs

During the early growth stage, lambs are highly susceptible to pathogenic microbial invasion due to an underdeveloped intestinal structure, unstable microbial colonization, and immature mucosal immune function, leading to diarrhea, growth retardation, and elevated mortality factors that severely constrain the production efficiency and economic viability of the sheep industry. This study aimed to compare the regulatory effects of compound yeast culture (CYC) and yeast polysaccharides (YPs) on intestinal barrier function in Mongolian male lambs and clarify their underlying molecular mechanisms. Eighteen lambs were randomly assigned to three groups (n = 6/group): control group (basal diet), CYC group (40 g/kg), and YP group (3 g/kg). After a 30-day feeding trial, intestinal histomorphology, tight junction proteins, immune signaling pathways, and gut microbiota were analyzed. The results showed that both additives improved intestinal villus morphology, and CYC markedly increased the villus height/crypt depth ratio (p < 0.05). At the mechanical barrier level, CYC upregulated the protein expression of occludin, claudin-1, and ZO-1, whereas YPs increased occludin and ZO-1 expression (p < 0.05). Immunologically, CYC inhibited intestinal inflammation via the TLR4/TRAF6/MyD88/NF-κB pathway, increasing interleukin-10 (IL-10) and secretory immunoglobulin A (sIgA) while decreasing pro-inflammatory cytokines. YPs exerted similar anti-inflammatory effects through the TLR2/MyD88 pathway. Microbial analysis indicated that both additives increased the relative abundance of beneficial bacteria including Eubacterium, Bacillus, and Succinivibrio, while reducing the potential pathogen Mogibacterium. Spearman correlation analysis revealed that Mogibacterium was positively correlated with TNF-α and negatively correlated with occludin expression. In conclusion, CYC and YPs effectively enhance intestinal mechanical, immune, and biological barriers via different TLR-mediated pathways and microbial modulation. Both natural additives have great application potential for improving lamb health, reducing antibiotic dependence, and promoting sustainable green animal husbandry.