ROLE OF PHOTOPERIOD AND EXERCISE IN CHANGES IN SERUM AMINOTRANSFERASE ACTIVITY IN MARES AND STALLIONS INVOLVED IN RECREATIONAL RIDING

The physiological response of horses to environmental and physical stimuli is a critical aspect of equine health and performance. Among the various factors influencing equine metabolism, photoperiod and exercise play an essential role in modulating biochemical and physiological parameters. Seasonal variations in enzyme activity, particularly aminotransferases, are of increasing interest in veterinary medicine and equine sport science as these enzymes serve as biomarkers of liver and muscle function. However, little research has investigated the combined effects of photoperiod and moderate exercise on aminotransferase activity in recreationally ridden horses, particularly considering sex differences. The aim of this study was to evaluate the role of photoperiod and exercise in modulating plasma aminotransferase activity in mares and stallions involved in recreational riding. By evaluating seasonal variations in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activity, this study aimed to elucidate potential physiological mechanisms underlying these changes and to explore sex differences. The study involved 21 healthy adult Shetland ponies (11 mares and 10 stallions) participating in recreational riding. Blood samples were taken before and after exercise in each season over a period of one year. Aminotransferase activity was analysed using standard biochemical assays and statistical analyses, including two-way ANOVA and Pearson’s correlation, were used to assess the effects of photoperiod, exercise and sex. Seasonal variations significantly influenced ALT and AST activity, with different responses between mares and stallions. In spring and summer, both sexes exhibited elevated pre-exercise aminotransferase levels, followed by moderate post-exercise fluctuations. In contrast, autumn and winter were characterised by a marked decrease in post-exercise aminotransferase activity, suggesting seasonal metabolic adaptations. Notably, mares and stallions showed different trends in enzyme activity, with stallions showing more pronounced fluctuations in AST levels, possibly related to testosterone-driven muscle metabolism. The results suggest that both photoperiod and exercise significantly influence aminotransferase activity in horses, with sex differences playing a crucial role. Seasonal metabolic adaptations appear to modulate enzymatic responses, which may have implications for training and health management of recreationally ridden horses. Future research should further investigate the endocrine mechanisms underlying these seasonal and sex-specific variations in order to optimise equine health and performance.