Environmental temperature and relative humidity differently affect the sperm characteristics in Brown Swiss and Belgian Blue bulls

In a temperature-increasing scenario, due to global warming, the individual thermic resilience of the male assumes a crucial role in the reproductive efficiency of a male since the thermic stress, such as the inability of the male to reduce body or regional temperature on a physiological level, impairs testicular function. In this study, the effect of the environmental conditions on the fresh semen quality, in terms of volume, concentration, total sperm in the ejaculate, total motility, normal morphology, membrane integrity, and discarding rate, were compared longitudinally in Belgian Blue (BB) and Brown Swiss (BS) bulls. The environmental conditions, summarized in the mean temperature-humidity index (THI), were calculated on the day of collection, as well as 7 days (epididymal maturation), 35 days (late spermatogenesis), and 70 days (early spermatogenesis) before the collection, to reflect spermatogenesis time. Our findings showed that limited seasonal effects were present in the semen quality of BS bulls. On the other hand, in BB bulls lower semen quality was found between July and November, with a different timing depending on the seminal parameter. This effect of the season on BB semen parameters appears to be related to the THI. The data presented in this study shows that the temperature and humidity, summarized in THI, could affect the semen quality of the bull on breed basis, given that volume, concentration, total sperm in the ejaculate, total motility, membrane integrity, and sperm normal morphology were significantly reduced by an increasing THI in the Belgian Blue bulls, but not in Brown Swiss bulls.