Insulating the scrotal neck affects semen quality and scrotal/testicular temperatures in the bull

Abstract

Nine Simmental X Angus bulls (2-yr of age) were used in 2 experiments. In Experiment 1, the scrotal neck was insulated (from Day 1 to Day 8) in 5 bulls, and semen was collected from all 9 bulls by electroejaculation approximately every 3 d until Day 35. Bulls with insulated scrotal necks had lower percentages of normal spermatozoa (P < 0.08) and higher percentages of spermatozoa with head defects (P < 0.06) or droplets (P < 0.08) than the untreated bulls. There was a time-by-treatment interaction (P < 0.04) for midpiece defects; the incidence was higher (P < 0.05) in the insulated than noninsulated bulls from Day 5 to Day 32. Spermatozoa within the epididymis or at the acrosome phase during insulation appeared to be the most affected. Compared with the noninsulated bulls, the insulated bulls had twice as many (P < 0.02) spermatozoa with midpiece defects and 4 times as many (not significant) with droplets on Day 5, fewer (P < 0.04) normal spermatozoa and 3 times as many with midpiece defects (P < 0.05) and with droplets (not significant) on Day 8, fewer (P < 0.02) normal spermatozoa on Days 15 and 18, and more sperm cells (P < 0.05) with head defects on Days 18 and 21. In Experiment 2, scrotal subcutaneous temperature (SQT; °C, mean ± SE) prior to and after the scrotal neck had been insulated for 48 h in all 9 bulls was 30.4 ± 0.7 and 32.4 ± 0.6 (P < 0.01) at the top, 30.3 ± 0.7 and 31.8 ± 0.6 (P < 0.03) at the middle, and 30.2 ± 0.8 and 30.7 ± 0.6 (P < 0.05) at the bottom of the scrotum. Concurrently, there was an increase (0.9 °C) in intratesticular temperature (ITT) at the top (P < 0.07), middle (P < 0.04), and bottom (P < 0.04) of the testes. Scrotal surface temperature (SST) prior to and after the scrotal neck had been insulated for 24 h was 29.2 ± 0.7 and 28.2 ± 0.4 (P < 0.05) at the top of the scrotum and 24.7 ± 0.6 and 25.3 ± 0.7 (not significant) at the bottom, resulting in SST gradients of 4.6 ± 0.6 and 2.9 ± 0.5, respectively (P < 0.05). However, after the scrotal neck had been insulated for 48 h, none of the SST end points were significantly different from those prior to insulation. It appears that compensatory thermoregulatory mechanisms restored SST but were not able to restore SQT and ITT. Insulation of the scrotal neck affected SST, SQT, ITT and semen quality, emphasizing the importance of the scrotal neck in scrotal/testicular thermoregulation.