Influence of thawing time and post-thaw temperature on acrosomal maintenance and motility of bovine spermatozoa frozen in .5-ml French straws.

The objective was to determine the relationship between thawing time and post-thaw temperature when the final temperature of the semen was brought to 40 C. One ejaculate from each of 12 dairy bulls was packaged in .5-ml French straws. Semen in five straws from each ejaculate was thawed in a 35 c water bath for 12 s or 1 min. The straws were then immediately placed in water baths at 0, 10 or 20 C for 1 min and then transferred to a water bath at 40 C for 1 min. Control treatments were thawed at (1) 35 C for 1 min, plunged into a 35 C water bath for 1 min and transferred to a final water bath at 40 C for 1 min, and (2) thawed at 40 C for 1 min, plunged into 40 C water bath for 1 min and transferred to a final water bath at 40 C for 1 min. Semen was incubated at 40 C and evaluated at 0, 4 and 8 h of incubation for percentage of motile spermatozoa (%MOT) and percentage of spermatozoa with intact acrosomes (PIA). Semen thawed at 35 C for 12 s and held at 0 C before being warmed to 40 C sustained immediate acrosomal damage (P less than .05) due to a delay in complete thawing of the semen. Semen thawed at 35 C for 1 min, held at 0 C and then warmed to 40 C also sustained immediate acrosomal damage which was due to cold shock. Cold shock damage was greater than damage due to a delay in complete thawing, therefore, precautions should be taken to prevent post-thawing cold shock. The 10 C post-thaw treatment resulted in spermatozoal damage with both thawing times, however, the effects were latent since damage was not observed until the 4- and 8-h evaluations. The 20 C post-thaw treatment did not decrease (P greater than .05) % MOT or PIA with either thawing time.