Integrated multi-omics analysis reveals the co-adaptive mechanisms between ruminal microbiota and host epithelium in water buffaloes under chronic heat stress

-N) concentration (HS vs. NHS, 4.44 vs. 7.86 mg/dL), an increased proportion of acetate (HS vs. NHS, 68.86 vs. 66.74%), and a decreased proportion of propionate(HS vs. NHS, 20.40 vs. 22.14%). Chronic heat stress imposed selective pressure on the ruminal microbial community, driving functional changes at the microbial level. The overall abundance of multiple CAZyme families increased, enhancing the potential for structural carbohydrate degradation; concurrently, the abundance of genes encoding key enzymes for pyruvate-to-acetyl-CoA conversion rose, consistent with elevated acetate synthesis potential; enrichment of nitrogen metabolism-related genes suggested enhanced microbial ammonia assimilation capacity. At the metabolic level, chronic heat stress induced specific metabolite dynamics, including decreased phosphatidylcholine PC(16:0/18:1(9Z)) content and accumulation of the flavonoid metabolite naringenin, indicating co-activation of phospholipid hydrolysis and flavonoid metabolic pathways. At the host level, transcriptional changes in rumen epithelium were primarily reflected in reduced ion transport capacity and enhanced cellular stress protection. In summary, the adaptive response of water buffaloes to chronic heat stress is primarily driven by the functional plasticity of the ruminal microbiome, which maintains energy supply and metabolic homeostasis to some extent by altering carbon and nitrogen metabolic fluxes; meanwhile, transcriptional regulation in the host rumen epithelium contributes to co-adaptation, though certain absorption-related functions may be compromised due to stress. These findings provide a biological basis for maintaining ruminal functional homeostasis and health in water buffaloes under high-temperature conditions through nutritional interventions.