Short communication: Lack of breed differences in responses of bovine spermatozoa to heat shock

An experiment was conducted to test whether the magnitude of effects of hea t shock on spermatozoal function were less for thermotolerant breeds (Brahm an and other breeds with Brahman influence) than for breeds that evolved in northern Europe (Angus and Holstein). Frozen spermatozoa were thawed, puri fied by Percoll gradient centrifugation and incubated at 38.5, 41, or 42 de grees C for 4 h. Sperm motility was then analyzed with a Hamilton Thorn Mot ility Analyzer. Heat shock reduced the percentage of sperm that were motile , mean track speed, and mean path velocity. There were no significant breed x temperature interactions for these traits. The mean frequency of tail be at tended to be reduced by heat shock in bulls of Brahman-influenced breeds and, to a lesser extent, in Brahman bulls, but it was not affected by heat shock in Angus or Holstein bulls. For no traits were there significant tem perature x bull within breed interactions. Overall, results indicate that 1 ) heat shock reduces motility of bovine spermatozoa and 2) genetic effects are unlikely to be an important determinant of the function of ejaculated s perm following heat shock.