Use of diagnostic tests is a crucial aspect of disease diagnosis in veterinary science since they assist the clinician to establish a confirmatory diagnosis. Diagnostic tests based on fluid generally use blood and urine and less frequently the other fluids such as oral fluid. “Oral fluid” is composed of saliva, gingival crevical fluids contained in the dentogingival sulcus, mucosal transudate, cell detritus, bacteria and food remains. Although saliva is predominantly a watery fluid, it also consists of a complex mixture of proteins, ions and other organic compounds produced mostly by the salivary glands with a small portion originating from the blood. The connection between local (salivary glands) and systemic (blood) sources makes saliva an important fluid for the diagnosis of diseases or to study a physiological status in particular. A huge advantage of saliva over blood is that it is easily accessible and can be obtained non-invasively and relatively stress-free. However, a major barrier in using saliva as a diagnostic fluid could be the fact that many informative analytes are generally present in lower amounts in saliva but with new and highly sensitive technologies, it is no longer a limitation.