Therefore, this study aims: (1) to validate assays for the measurement of selected biomarkers of oxidative status in saliva and, for comparative purposes, serum of horses; (2) to assess the possible differences in these analytes if suffering from EGSG, EGGD, or CIE; (3) to evaluate the possible relationship of these analytes in serum and saliva with the inflammation status assessed by the serum amyloid A (SAA) [5,17] or their systemic inflammatory response status (SIRS) [18], and with a biomarker of cell-mediated immunity such as adenosine deaminase (ADA) [4,19,20]. Here, ADA is linked to systemic inflammatory response syndrome.