Relationships between climate and sperm quality in dairy bull semen: A retrospective analysis

The aim of the present study was to make a retrospective analysis of the relationship between climatic factors and sperm quality of frozen–thawed semen from bulls kept in temperate climates. Semen samples from 21 European dairy bulls from 2 countries were collected and cryopreserved in winter, spring, and summer. Sperm quality parameters such as kinematics, morphology, plasma membrane integrity, mitochondrial membrane potential, sperm chromatin structure assay, and reactive oxygen species were analyzed and correlated retrospectively with climate factors recorded by the local meteorological office. This study demonstrated that sperm quality parameters are more likely to be correlated with climate factors 1 or 2 mo before semen collection than in the month of semen collection. During the month of sperm collection, sperm kinematics, DNA fragmentation, and hydrogen peroxide production were the only sperm quality parameters related to climate factors, whereas 1 and 2 mo before sperm collection, normal morphology and additional sperm kinematics, in addition to DNA fragmentation and hydrogen peroxide production, were correlated with climate factors. In conclusion, dairy bull sperm quality is affected by climatic conditions, even in so-called temperate zones. The timing of heat stress during spermatogenesis determines which aspects of sperm quality are likely to be affected. Husbandry conditions for bulls used for semen collection should be adapted to allow the animals' physiological responses for temperature regulation within the scrotum to operate fully, to mitigate the effects of increased temperature and humidity. Extremes of temperature should be avoided.