SEASONAL AND SEX-BASED VARIATION IN MUSCLE METABOLISM MARKERS IN HORSES BEFORE AND AFTER EXERCISE

Key modulators of muscle metabolism in equines include seasonal environmental changes, biological sex and physical exertion. Indicators such as lactate dehydrogenase (LDH), lactate and pyruvate offer valuable insights into physiological adaptations and metabolic stress during exercise. The present study aimed to evaluate the influence of seasonality, sex and exercise on LDH activity and lactate and pyruvate concentrations in Shetland ponies. Blood samples were collected from 21 clinically healthy ponies (11 mares and 10 stallions) before and after standardised exercise sessions conducted in spring, summer, autumn and winter. LDH was assayed in serum, while lactate and pyruvate were analysed in whole blood. Paired t-tests, ANOVA and post hoc Tukey HSD tests were performed to evaluate intra- and intergroup differences. Pearson correlations and effect size analyses were applied to assess seasonal and physiological associations. Exercise led to significant increases in lactate and LDH levels, particularly in spring and autumn. Pyruvate showed mild but consistent post-exercise elevations. There was a pronounced seasonal influence: winter stallions had the highest LDH values, while summer mares exhibited elevated lactate levels, suggesting heat-related stress. Sex differences were modest yet significant, with stallions displaying higher mean LDH and pyruvate levels overall. LDH, lactate and pyruvate are sensitive biomarkers of muscular activity and seasonal adaptation. Their variation across seasons and between sexes reflects physiological stress responses and could inform training strategies, veterinary assessments and breeding decisions in equine practice.