Cystatin C, Ammonia, and Bicarbonate Measurements in the Saliva of Pigs: Analytical Validation and Changes in S. suis Infection.

Cystatin C, ammonia, and bicarbonate have been described to be biomarkers of sepsis and inflammation in humans. The saliva of pigs can be used to detect a wide range of pathogens but also many biomarkers that can be analyzed to evaluate different conditions such as stress (i.e., cortisol and alpha amylase), immune system (i.e., ADA, S100 proteins), inflammation (i.e., acute phase proteins), redox status (i.e., various antioxidants and oxidants), and general metabolism or the status of different organs and tissues. However, there is a lack of assays for the possible measurement and use of cystatin C, ammonia, and bicarbonate in saliva as biomarkers of sepsis or inflammation in pigs. The objective of this study was to validate commercially available automated assays for the measurement of cystatin C, ammonia, and bicarbonate in the saliva of pigs, having the advantage of using a noninvasive sample that is easy to collect. The assays were precise and accurate, and the recommended storage condition for the saliva samples was -80 °C. In addition, cystatin and ammonia showed significant increases in the saliva of pigs with S. suis infection, whereas bicarbonate decreased. Further studies would be recommended to increase knowledge about the possible potential applications of the measurements of these three analytes in the saliva of pigs as biomarkers to evaluate the animals' health and welfare.