CONTRIBUTION OF THE SCROTUM, TESTES, AND TESTICULAR ARTERY TO SCROTALTESTICULAR THERMOREGULATION IN BULLS AT 2 AMBIENT-TEMPERATURES/

The objective of this study was to determine the contribution of the s crotum, testes, and the testicular artery to scrotal/testicular thermo regulation in bulls at two ambient temperatures. Crossbred beef bulls, 1.5 years of age, were placed in controlled environment chambers at a mbient temperatures of 15 degrees C (n = 5) or 25 degrees C (n = 6). T he distal lateral aspects and entire ventral part of the scrotum was i ncised under caudal epidural anaesthesia (xylazine, 0.07 mg kg(-1)). B oth testes were withdrawn from the scrotum and then replaced and maint ained by clamping the scrotal incisions with towel clamps. One testis was randomly chosen to be the exposed testis and was withdrawn prior t o temperature measurements. Surface and internal temperatures were mea sured with infrared thermography and needle thermocouples, respectivel y. Temperature gradients (degrees C; difference in temperature from to p to bottom at 15 and at 25 degrees C) were: scrotal surface (with tes tis), 1.5 and 1.3; scrotal surface (without testis), 2.1 and 1.6; surf ace 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 intrates ticular (exposed testis), -1.3 and 0.4. The scrotum markedly affects t esticular temperature but the testes have limited influence on scrotal surface temperature. The bovine scrotum and testes have opposing temp erature gradients that complement one another, resulting in a relative ly uniform intratesticular temperature. These temperature gradients ar e attributed in part to the testicular artery, which goes from the top of the testis to the bottom, divides into several branches and ramifi es dorsally and laterally before entering the testicular parenchyma. I ntra-arterial temperatures (measured with needle thermocouples) were l ower (P < 0.05) where the artery entered the testis than at both the b ottom and top of the testis for both the covered (31.7, 33.4 and 34.3 degrees C) and exposed testis (29.6, 32.0 and 32.5 degrees C) at an am bient temperature of 15 degrees C. Temperature differences were simila r, but less pronounced, at 25 degrees C (covered testis, 34.8, 36.3 an d 36.5 degrees C; exposed testis, 32.4, 33.5, 33.9 degrees C). Results supported the hypothesis that blood within the testicular artery has a similar temperature at the top of the testis (just ventral to the te sticular vascular cone) compared with the bottom, but subsequently coo ls before entering the testicular parenchyma.