Contribution of the scrotum, testes, and testicular artery to scrotal/testicular thermoregulation in bulls at two ambient temperatures.

摘要

Crossbred beef bulls, 1.5 years of age, were placed in controlled environment chambers at ambient temperatures of 15鳦 (5 bulls) or 25鳦 (6 bulls). The distal lateral aspects and entire ventral part of the scrotum was incised under caudal epidural anaesthesia (xylazine, 0.07 mg/kg). Both testes were withdrawn from the scrotum and then replaced and maintained by clamping the scrotal incisions with towel clamps. One testis was randomly chosen to be the exposed testis and was withdrawn before temperature measurements. Surface and internal temperatures were measured with infrared thermography and needle thermocouples, respectively. Temperature gradients (鳦; difference in temperature from top to bottom at 15 and at 25鳦) were: scrotal surface (with testis), 1.5 and 1.3; scrotal surface (without testis), 2.1 and 1.6; surface of exposed testis, -0.6 and 0.0; sub-tunic of exposed testis, -2.2 and -0.6; intratesticular (covered testis), 0.0 and 0.4; and intratesticular (exposed testis), -1.3 and 0.4. Itis concluded that the scrotum markedly affects testicular temperature but the testes have limited influence on scrotal surface temperature. Intra-arterial temperatures (measured with needle thermocouples) were lower where the artery entered the testis than at both the bottom and top of the testis for both the covered (31.7, 33.4 and 34.3鳦) and exposed testis (29.6, 32.0 and 32.5鳦) at an ambient temperature of 15鳦. Temperature differences were similar, but less pronounced, at 25鳦 (covered testis, 34.8, 36.3 and 36.5鳦; exposed testis, 32.4, 33.5, 33.9鳦). Results supported the hypothesis that blood within the testicular artery has a similar temperature at the top of the testis (just ventral to the testicular vascular cone) compared with the bottom,but subsequently cools before entering the testicular parenchyma.