Scrotal surface, subcutaneous, intratesticular, and intraepididymal temperatures in bulls

Abstract

Sixteen 2-yr-old beef bulls were used in the study. Under caudal epidural analgesia (xylazine HCl, 40 mg), infrared thermography was used to determine scrotal surface temperature (SST) and needle thermistors were used to determine scrotal subcutaneous (SQT) and intratesticular (ITT) temperatures at 3 locations on the posterior aspect of the scrotum: 3 cm from the top of the testis, 3 cm from the bottom of the testis, and at the midpoint of the testis. Average temperatures (°C) at the top, middle and bottom locations were 30.4 ± 0.4, 29.8 ± 0.6 and 28.8 ± 0.8 (SST); 33.3 ± 0.2, 33.0 ± 0.2 and 32.9 ± 0.3 (SQT); and 34.3 ± 0.1, 34.3 ± 0.1 and 34.5 ± 0.1 (ITT). Correlation coefficients between SST and SQT were moderate to high, those between SQT and ITT were low to moderate, and those between SST and ITT were low. Therefore, caution must be exercised when making inferences about ITT based on measurement of SST. The temperature gradient from top to bottom was most pronounced for SST (1.6 °C), smaller for SQT (0.4 °C), and slightly negative (relative to the surface) for ITT (−0.1 °C). These gradients may be due to the arrangement of the vasculature; the scrotum is apparently vascularized from the dorsal pole of the testis to the ventral pole, while the testicular artery ramifies dorsally from the bottom of the testis to the top. Intraepididymal temperatures (IET) of the head, body and tail of the epididymis averaged 35.6 ± 0.2, 34.6 ± 0.1 and 33.1 ± 0.3 °C. The head of the epididymis was warmer than the testicular parenchyma, but the tail, an important storage site for spermatozoa, was cooler.