Effect of Wet-Bulb Globe Temperature Index (WBGTi) on the seminal quality of Quarter Horse stallions in Los Tuxtlas region, Veracruz

The study aimed to evaluate the effect of climate, measured through the Wet-Bulb Globe Temperature index (WBGTi), on the seminal quality of Quarter Horses in a horse farm located in Los Tuxtlas, Veracruz, in a tropical environment. Meteorological variables, including ambient temperature and relative humidity, were assessed over nine years (2013-2021) to determine the daily and monthly average WBGTi. These values were then related to the macroscopic (volume) and microscopic characteristics (motility percentage, vitality, normal spermatozoa, and sperm concentration) of semen obtained from five stallions. A thermally comfortable environment (WBGTi <= 26.99), falling within the thermoneutral zone of horses, was observed from December to February. In contrast, from March to October, the environment was classified as thermally cautious or stressful (WBGTi = 27 to 36.80). A significant difference (p <= 0.05) was found in the percentage of mobility (73.75 +/- 2.58 vs 67.25 +/- 1.29 in precautionary environment and 65.99 +/- 3.32 in stressful environment), vitality (79.62 +/- 2.22 vs 74.71 +/- 1.10, 73.69 +/- 2.82) and normal spermatozoa (66.95 +/- 1.55 vs 62.84 +/- 0.78, 61.51 +/- 1.99), being lower during the warmest period. Sperm volume and concentration were not significantly affected by the WBGTi increase, and none of the seminal characteristics exhibited seasonal patterns. It was concluded that an increase in heat, as measured by WBGTi, negatively impacted the seminal quality of stallions.