Contribution of the scrotum and testes to scrotal and testicular thermoregulation in bulls and rams.

A novel model was used to determine the role of the scrotum and testes in scrotal/testicular thermoregulation in bulls and rams. Eleven yearling bulls and 12 yearling rams were used at an ambient temperature of 15 degrees C. The distal lateral aspects and entire ventral part of the scrotum were incised under caudal epidural analgesia (xylazine, 0.07 mg ml-1). Both testes were withdrawn from the scrotum, the vaginal tunic was removed and one testis was replaced in the scrotum. Surface and internal temperatures were measured with infrared thermography and needle thermocouples, respectively. Temperature gradients (difference in temperature from top to bottom; degree C) for bulls and rams, respectively, were: scrotal surface (with replaced testis) 2.1 and 3.5; scrotal surface (without testis) 2.5 and 3.6; scrotal subcutaneous (with replaced testis) 1.0 and 0.7; testicular subtunic (without scrotum) -0.7 and -0.3; deep intratesticular (with scrotum) -0.2 and -0.6; and deep intratesticular (without scrotum) -0.5 and -0.5. Results supported the hypotheses that the scrotum has a positive temperature gradient (warmer at the top than the bottom) and that the testis has a negative temperature gradient (warmer at the bottom than the top). These opposing gradients apparently complement one another, resulting in a relatively uniform intratesticular temperature, below body core temperature, that is essential for normal sperm production. The scrotum substantially increased intratesticular temperature, but scrotal surface temperature was not significantly affected by the presence of a testis.