Dietary exopolysaccharides alleviate SARA-induced colonic dysfunction in Hu sheep by modulating microbiota and enhancing barrier integrity.

Subacute ruminal acidosis (SARA) induced by high-concentrate feeding impairs hindgut fermentation, disrupts epithelial barrier function, and promotes inflammation in ruminants. Exopolysaccharides (EPS) produced by lactic acid bacteria have emerged as potential postbiotic additives that may enhance gut health, yet their effects on the hindgut during SARA remain unclear. This study evaluated whether dietary EPS supplementation could mitigate colonic dysfunction in Hu sheep exposed to a high-concentrate diet. Twenty sheep were randomly assigned to four groups: low-concentrate diet (LCD), high-concentrate diet (HCD; concentrate-to-forage ratio 7:3), and HCD supplemented with 0.1% (LEPS) or 0.2% EPS (HEPS) for 5 weeks. The HCD group showed typical SARA symptoms (ruminal pH <5.6 for >3 h/d), increased LPS levels, elevated oxidative stress (higher MDA, lower T-AOC), and upregulated proinflammatory cytokines (TNF-α, IL-6, IL-2, IFN-γ). Tight junction genes (ZO-1, claudin-4, claudin-7) and proteins were downregulated, and the microbiota exhibited dysbiosis. EPS supplementation, particularly at 0.2% level, effectively alleviated these effects by maintaining ruminal pH, reducing LPS, improving antioxidant capacity, and suppressing inflammation. HEPS increased beneficial and short-chain fatty acid-producing bacteria, upregulated tight junction proteins, and inhibited NF-κB activation. Moreover, EPS reduced H3K56 and H4K8 acetylation and promoted chromatin condensation at TNFA and IL6 promoters, suggesting epigenetic repression of inflammatory gene transcription. In conclusion, EPS attenuated the detrimental effects of SARA on colonic integrity and inflammatory status, implying that microbial EPS may serve as a promising postbiotic strategy to support hindgut health in ruminants fed high-concentrate diets.