Effects of Exercise on Ocular Parameters and Oxidative Stress Biomarkers in Saliva and Tear Fluid of Horses

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BACKGROUND: Physical exercise is a physiological stressor in horses and may induce oxidative stress through increased production of reactive oxygen species. Saliva and tear fluid are accessible non-invasive matrices that may reflect oxidative balance, while ocular parameters including intraocular pressure (IOP), tear secretion (TS) and central corneal thickness (CCT) are key components of ocular homeostasis. OBJECTIVE: To evaluate the effects of a standardised submaximal exercise session on IOP, TS and CCT, and on oxidative stress biomarkers (CAT, SOD, GSH, MDA, IMA) measured in saliva and tear fluid. METHOD: Thirty-six clinically healthy Arabian horses underwent a 30-min submaximal field exercise (walk-trot-canter). Heart rate, ocular parameters (Schirmer tear test-1, rebound tonometry, ultrasonic pachymetry) and saliva and tear fluid samples were collected immediately before and after exercise. Data normality was assessed using the Shapiro-Wilk test, and paired-samples t-tests or Wilcoxon signed-rank tests were applied as appropriate. RESULT: Heart rate increased significantly after exercise (p < 0.001). IOP and CCT did not change significantly, whereas TS decreased modestly (p = 0.033). In saliva, CAT and SOD increased and MDA decreased (all p < 0.001), with no changes in GSH or IMA. In tear fluid, CAT, GSH and SOD increased, while IMA and MDA decreased significantly. CONCLUSION: Submaximal exercise elicited antioxidant-dominant shifts in both saliva and tear fluid, while ocular parameters remained largely stable except for a mild reduction in TS. Tear fluid, alongside saliva, may provide complementary information on exercise-associated physiological and oxidative responses in horses under routine training conditions.