Effect of heat shock on function of frozen/thawed bull spermatozoa

Deposition of spermatozoa in the reproductive tract of hyperthermic cows could conceivably result in sperm damage. Accordingly, a series of experiments tested the effects of heat shock on functional characteristics and free radical production of bull spermatozoa. Viability was reduced slightly by short-term (1 to 3 h) culture at 42 and 43 °C as compared with culture at 39 °C. There was no effect of culture at 42 °C on the ability of spermatozoa to undergo swim-up or of 42 °C on the percentage of motile spermatozoa. However, exposure to 41 °C for 3 h reduced percentage of motile sperm, 41 and 42 °C reduced sperm velocity and 43 °C decreased the proportion of spermatozoa undergoing swim-up. In other experiments, there was no effect of heat shock (41 or 42 °C for 1 to 3 h) on DNA integrity, presence of intact acrosomes, or fertilizing ability of the spermatozoa. Superoxide production by spermatozoa was higher at 42 °C than at 39 or 41 °C, but there was no detectable hydrogen peroxide production at any temperature. The antioxidant, glutathione, tended to improve the ability of spermatozoa to undergo swim-up at 39 °C but not at 43 °C. Taken together, these results suggest that heat shock of a magnitude similar to that seen in vivo (41 to 42 °C) has little effect on sperm functions that affect fertilizing capability.