Thermal comfort and seminal traits in stallion reproduction: New methods to understand these relationships.

BACKGROUND

Stallion breeding is mostly based on desirable phenotypic traits, with little consideration for semen quality.

AIMS/

OBJECTIVES

To identify relationships among semen parameters in stallions using a non-invasive, integrative approach across summer and winter seasons.

METHODS

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 (coat weather) and summer (T-shirt weather). Statistical tests included univariate and multivariate analyses in software SPSS® (IBM).

RESULTS

Sperm defects (22.4 ± 7.3 %) and heat stress indices (THI: 79.7 ± 3.4; ThStress: 2.9 ± 0.7) were higher in summer (28.6 ± 2.7 °C) than in winter (12.5 ± 9.4 %; 21.1 ± 2.4 °C; THI: 73.5 ± 8.6; ThStress: 1.1 ± 0.3). The heat stress indices were calculated by the equation: THI= [0.8 x (EnTemp + RH/100)] x [(EnTemp - 14.4) + 46.4]. In contrast, systolic/diastolic testicular blood flow velocities, motility, and vigor were greater in winter (33.3 ± 9.3 cm/s; 5.9 ± 2.2 cm/s; 81.2 ± 8.5 %; 3.2 ± 0.4) than in summer (24.4 ± 6.7 cm/s; 4.0 ± 1.0 cm/s; 64.2 ± 21 %; 2.7 ± 0.6). Significant correlations were found between thermal comfort indices and seminal traits in summer, and between Doppler/thermographic data and semen quality in winter.

CONCLUSION

The analyzed indices characterized thermal, circulatory, and seminal parameters in stallions, highlighting seasonal differences and correlations, and supporting the use of Doppler ultrasonography and infrared thermography in fertility assessment, thermal comfort, and optimal breeding season selection.