Effects of Scrotal Insulation on Viability Characteristics of Cryopreserved Bovine Semen

¹ Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061

The effect of a 48-h scrotal insulation on spermatozoal viability (motility and acrosomal integrity), before and after semen cryopreservation, was studied in six young Holstein bulls whose semen was collected twice in succession at 3-d intervals. Motility and acrosomal integrity were measured before and after incubation of semen at 37°C for 3 h. For assessment of results, collection days were grouped: period 1 (control) = d –6, –3, and 0, where d 0 = initiation of scrotal insulation after semen collection; period 2 = d 3,6, and 9 (sperm presumed in the epididymis or rete testis during scrotal insulation); period 3 = d 12, 15,...39 (sperm presumed in spermatogenesis during scrotal insulation). Semen was cryopreserved each collection day until morphologically abnormal cells exceeded 50% of the ejaculate (d 12 to 21). Semen viability before and after freezing was lower in period 3 than in period 1 (P < .05). These differences coincided with the appearance in period 3 of abnormal sperm morphology and depressed undiluted semen motility, which began on d 12 (P < .01). Semen collected during period 2 that was extended but unfrozen did not differ from that collected during period 1 in morphology or viability. However, for frozen semen, period 2 was significantly poorer than period 1 for both viability measurements, but only after incubation for 3 h at 37°C postthaw (P < .05). We conclude that epididymal sperm are adversely affected by elevated testicular temperatures, as noted by their decreased ability to maintain motility and acrosomal integrity following cryopreservation.

Key Words: bovine • thermal stress • semen viability • frozen semen

Submitted on May 9, 1991
Accepted on June 14, 1991