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 heat shock on spermatozoal function were less for thermotolerant breeds (Brahman and other breeds with Brahman influence) than for breeds that evolved in northern Europe (Angus and Holstein). Frozen spermatozoa were thawed, purified by Percoll gradient centrifugation and incubated at 38.5, 41, or 42 degrees C for 4 h. Sperm motility was then analyzed with a Hamilton Thorn Motility 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 beat 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 temperature 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 sperm following heat shock.