THERMAL COMFORT AND SEMINAL TRAITS IN STALLION REPRODUCTION: NEW METHODS TO UNDERSTAND THESE RELATIONSHIPS

Stallion breeding is mostly based on desirable phenotypic traits, with little consideration for semen quality. This study aimed to identify the relationships between different semen parameters in equine reproduction, using non-invasive methods, during summer and winter, using an integrative approach. Twenty-four stallions were evaluated, in which semen collections, testicular thermography, and Doppler velocimetry of the testicular artery by Doppler ultrasonography were performed, in addition to the measurement of physiological, environmental, and heat stress parameters, both in winter and summer. Statistical tests included univariate and multivariate analyses in SPSS® software (SPSS, 2012). Sperm defects, environmental temperature, and heat stress indices were higher in summer than in winter. In contrast, systolic and diastolic velocities, sperm motility, and vigor were higher in winter, which was attributed to the increase in environmental temperature and mean testicular temperature in summer. Environmental and thermal comfort variables showed significant correlations with seminal parameters in summer. In winter, there was a significant correlation between Doppler-measured variables, motility, vigor, and testicular temperature assessed by thermography. The analyzed indices characterized the thermal, circulatory, and seminal parameters of stallions, evidencing their differences and correlations between the seasons of the year, providing relevant data for the introduction of Doppler ultrasonography and infrared thermography in the evaluations of stallion fertility, thermal comfort, and choice of the ideal season for reproduction. Hypothesis: Exposure to high environmental temperatures, especially in summer, is expected to negatively influence the sperm quality of stallions. Non-invasive methods, such as thermography and Doppler ultrasonography, can effectively detect these changes, contributing to adequate reproductive management.