Unlocking the Immunomodulatory Potential of Lactic Acid Bacteria in Livestock and Poultry: Mechanisms and Implications

ABSTRACT: The increasing pressure to reduce antibiotic use in livestock and poultry production has intensified interest in lactic acid bacteria (LAB) as promising microbial interventions for improving animal health. Although accumulating evidence indicates that LAB can regulate host immunity, maintain intestinal barrier function, and enhance disease resistance, the underlying mechanisms remain incompletely understood, and their effects are influenced by bacterial strains, host species, dietary conditions, and other factors. Here, we comprehensively summarize the immunomodulatory mechanisms of LAB, with particular emphasis on the direct mechanisms through which microbial components interact with host immune signaling and cellular responses, as well as the indirect mechanisms through which LAB modulate the gut microbiota and its metabolic outputs. We further discuss the importance of strain specificity in determining the functional properties and immunomodulatory effects of LAB. In addition, we review the practical applications of LAB in livestock and poultry production and highlight the major challenges and limitations associated with their application. By integrating mechanistic insights with practical considerations, this review offers new perspectives on the rational application of LAB to improve immune function and animal health in livestock and poultry production.