The Impact of Testicular Hyperthermia and Its Physiological Relevance to Human and Agriculture

Testicular heat stress is a well-known and well-described phenomenon that occurs in mammals that possess a scrotum. Different models to induce testicular hyperthermia, such as surgical cryptorchidism, hot water bath, scrotal insulation or increased environmental temperature have all shown that spermatocytes and spermatids are unambiguously affected by high temperature, resulting in poor sperm production weeks later. The testis appears to be very sensitive to temperature fluctuations, as even small changes in scrotal temperatures cause a drop in sperm counts, motility, and morphology. The higher the temperature and longer the during of heat, the more pronounced the effect in terms of semen quality. Whilst "experimental" models seem to validate the effect of testicular heat stress on sperm quality, the physiological relevance of testicular hyperthermia is still debated. Herein we summarise a cohort of studies that report the effect of "season" on sperm quality. The data show season can affect semen quality depending on where the work was performed. In countries where temperatures drop below zero, there is evidence to show that summer conditions tend to improve semen quality. However, in sup-tropical countries, there is some debate; some studies showing decreases in summer, whilst others show no change. Herein we offer an explanation as to explain this apparent discrepancy. Furthermore, we present data that show individual animals can show a "spectrum" of tolerance when it comes to spermatogenesis and testicular hyperthermia.