Salivary Biomarkers in Ruminants: A Review

Abstract

Saliva is increasingly investigated as a non-invasive biological sample for assessing health and physiological status in domestic ruminants. Its collection is relatively simple, minimally stressful, repeatable and potentially suitable for individual monitoring, herd-level surveillance and on-farm testing. Salivary constituents reflect systemic physiological and pathological changes, thereby providing information on animal welfare, metabolism, immunity and disease status. However, the diagnostic value of saliva can be influenced by species, diet, feeding status, salivary flow, sampling time, oral contamination, collection device, sample processing, handling, transport and storage conditions. The present review summarizes salivary biomarkers evaluated in ruminants, including cortisol, salivary alpha-amylase, butyrylcholinesterase, total esterase activity, antioxidant-capacity measures, haptoglobin, adenosine deaminase, immunoglobulin A, lactoferrin, electrolytes, progesterone, pathogen-derived nucleic acids, antigens, antibodies and host-response molecules. These biomarkers are associated with stress and welfare, oxidative status, inflammation and tissue injury, immune activity, reproductive status and parasitic and infectious diseases. The review also covers composition and physiological functions of saliva in cattle, buffaloes, sheep and goats along with the principal collection methods and key pre-analytical factors affecting salivary analysis. Consequently, standardized sampling and analytical procedures, species-specific reference values and validation in larger field populations are required to establish the reliability of salivary biomarkers. The development of simple collection devices and rapid, cost-effective point-of-care assays could facilitate their direct use on farms for routine ruminant health surveillance, earlier detection of health problems and faster decision-making.