Effect of age and disease on saliva and serum biomarkers of stress, inflammation, immunity, redox and general health status in pigs

Saliva is gaining importance as a complementary or alternative sample to serum for biomarker analysis. However, there is still a lack of knowledge about the possible relations between saliva and serum in health and disease. In this report, a total of 21 biomarkers were studied in saliva and serum from three groups of healthy pigs with different ages (T0, recently weaned pigs, 15 females and 15 males; T1, intermediate nursery, 15 females and 15 males; and T2, fattening period, 15 females and 15 males) and in a group of animals with Actinobacillus pleuropneumoniae (A. pp.) infection (intermediate nursery, 20 females). Sex of the animals did not significantly influence the results in either saliva or serum from healthy animals. In healthy pigs, the α-amylase (AA), ferric reducing ability (FRA), Urea, Triglycerides, Calcium (Ca) and Phosphorous (P) showed a similar dynamic in saliva and serum across fattening, whereas Butyrylcholinesterase (BChE), Adenosine deaminase (ADA), Immunoglobulin G (IgG), C-reactive protein (CRP), Haptoglobin (Hp), Total protein (TP), Myeloperoxidase (MPO), Ferritin, the Advanced oxidation protein products (AOPP), Uric acid (UA), Aspartate aminotransferase (AST), Creatine kinase (CK), Lactate dehydrogenase (LDH), Alkaline phosphatase (ALP) and γ-glutamil transferase (gGT) showed a different dynamic between serum and saliva. In pigs with A. pp infection, saliva showed significant changes in more analytes than serum, with AA, ADA, MPO, AST, LDH and Ca showing significant increases only in saliva. Differences in sensitivity to detect A. pp. infection were found in some selected analytes between saliva and serum. Biomarkers can show different changes in saliva and serum depending on age, and they can show different responses to disease between saliva and serum.