Microbial and Metabolic Dysbiosis in Ruminal Acidosis: Mechanisms, Host Responses, and Microbiota-Targeted Mitigation Strategies

Ruminal acidosis, particularly subacute ruminal acidosis, remains a major metabolic disorder that compromises animal health, production efficiency, and the sustainability of intensive ruminant systems. Although traditionally defined by reduced ruminal pH, it is increasingly recognized as a multidimensional disorder involving microbial ecological destabilization, disrupted metabolic cross-feeding, impaired epithelial barrier function, and dysregulated host inflammatory responses. This review synthesizes current knowledge of the microbial and metabolic mechanisms underlying acute and subacute ruminal acidosis and highlights processes that extend beyond pH depression alone. High-concentrate feeding shifts the balance among amylolytic and lactate-producing microorganisms, lactate-utilizing populations, and fibrolytic guilds, thereby promoting organic acid accumulation, reducing functional redundancy, and weakening microbial resilience. Concurrent increases in volatile fatty acids, lactate, lipopolysaccharide, histamine, and other microbially derived bioactive compounds increase epithelial acid load, disrupt tight-junction integrity, and facilitate inflammatory signaling. The principal novelty of this review is the integration of microbial functional guilds, metabolic cross-feeding, ecological resilience, epithelial barrier dysfunction, and host inflammation into a unified microbiota–metabolism–barrier–inflammation framework linking dietary perturbation with microbial dysfunction and host pathology. We further critically evaluate nutritional regulation, buffering agents, probiotics, yeast-derived products, postbiotics, and plant bioactive compounds according to their capacity to restore microbial function rather than merely correct ruminal pH. Additionally, this review may support multidimensional risk assessment, guide targeted intervention, and facilitate the integration of continuous ruminal monitoring with precision nutrition for earlier prediction and individualized prevention of ruminal acidosis.