Association Between Vaquejada Practice and Biomarkers of Oxidative Stress, Inflammation, and Muscle Damage in Quarter Horses

Vaquejada (VQ) is a traditional Brazilian sport demanding high performance from Quarter Horse (QH) athletes. This study aimed to identify modifications in hematological, biochemical, inflammatory, and oxidative stress biomarkers associated with VQ training, comparing conditioned and non-conditioned horses. Blood samples were collected at rest from 70 healthy QH horses: 60 athletes (VQ-conditioned athlete group—AG) and 10 sedentary controls (breeding horses—CG). Using Linear Mixed Models alongside comprehensive hematological and biochemical analyses, the study found that AG horses exhibited an altered homeostatic profile, characterized by significant reductions in erythrocytes (7.0 [2.7] vs. 8.0 [1.6]; p = 0.021), lymphocytes (33.0 [21.0] vs. 41.0 [25.0]; p = 0.028), and the antioxidant enzymes catalase (1.5 [0.5] vs. 2.4 [1.4]; p = 0.026) and myeloperoxidase (141.5 [53.9] vs. 235.6 [30.4]; p = 0.022) relative to CG. Conversely, marked increases were observed in band neutrophils (59.0 [16.0] vs. 49.0 [27.0]; p = 0.028), platelets (276.0 [115.0] vs. 160.0 [113.6]; p = 0.026), and malondialdehyde levels (177.5 [211.8] vs. 1475.0 [802.5]; p < 0.001), evidencing lipid peroxidation. These findings indicate that VQ induces severe oxidative stress and compromises immune functions, with horses presenting oxidative rather than inflammatory damage. Dietary monitoring is therefore recommended to mitigate such effects at 96 h post-exercise.