Thermoregulation of the Testes

Regulation of testicular temperature is dependent on several features. Scrotal skin is typically thin, with minimal hair and an extensive subcutaneous vasculature, facilitating heat loss by radiation. Sweating and whole-body responses contribute to testicular cooling. Testicular blood flow and O2 uptake were measured in eight Angus bulls to determine the relative importance of blood flow versus metabolism as sources of testicular heat. Infrared thermograms of the scrotum of bulls with apparently normal scrotal thermoregulation were symmetrical left to right, with temperature at the top 4-6 °C warmer than at the bottom. Infrared thermography is a useful tool for breeding soundness evaluation of bulls, although it does not replace collection and evaluation of semen. Scrotal insulation is frequently used to increase testicular temperature. When scrotal/testicular temperature is increased, sperm morphology is generally unaffected initially but subsequently declines.