The Salivary Microbiota–Host Nexus: Unraveling Opportunities for Non-Invasive Monitoring of Health and Productivity in Farm Animals

Salivary microbiota constitutes complex microbial assemblages and acts as a source of reliable non-invasive biomarkers for evaluating growth, metabolism, and health status of farm animals. This review explores the research value of saliva and its resident microbes in livestock health monitoring. We summarize saliva composition, physiological functions, and sampling protocols for pigs, cattle, sheep, and goats. Core microbial taxa of monogastric and ruminant species are outlined, together with their roles in digestion, rumen fermentation, growth, and stress responses. We also present classic salivary diagnostic indicators and the impacts of oral bacteria on common livestock diseases. Current research is limited by undefined causal relationships, low diagnostic specificity, and heterogeneous technical standards, and thus fails to support accurate diagnosis at the individual animal level. Future studies should elucidate microbial interaction mechanisms, standardize experimental protocols, and establish multi-index evaluation models. This review advances theoretical research and promotes the practical application of salivary microbiota in precision livestock farming.