Effect of various cooling rates (from 30°C to 5°C) and thawing temperatures on the deep-freezing of [formula omitted][formula omitted] and [formula omitted][formula omitted] semen

Abstract

A total of 36 semen ejaculates, six from each of three Holstein-Friesian bulls and three Murrah buffalo bulls, were frozen in tris citric acid-fructose-egg-yolk-glycerol diluent after 1 hour of equilibration to study the effect of various cooling rates (15, 30, 60 and 120 minutes from 10° to 5°C vs a control sample cooled for 120 minutes from 28° to 5°C) and thawing temperatures ( 40° C 60 seconds , 60° C 15 seconds and 80° C 5 seconds ) on prefreeze and post-thaw sperm motility. Sperm motility differed significantly (P < 0.01) between various cooling rates in both the Holstein-Friesian bull semen and the Murrah buffalo semen at prefreezing, immediately post-thawing, and after 1 hour of post-thaw incubation at 38°C. Post-thaw sperm motility and survival at 38°C were significantly (P<0.01) higher in Holstein-Friesian bulls at 60°C and 80°C than at 40°C (39.79±2.46% and 38.15±2.18% Vs 35.16±2.19%, and 20.22±2.14% and 19.05±2.05% vs 14.83±1.64%, respectively). In Murrah buffalo bulls the recovery percentage and survival rate increased significantly (P<0.01) with the increase in temperature from 40°C to 80°C (41.72±2.45%, 47.45±2.09% and 51.61±2.06%; and 9.22±1.47%, 11.79±1.63% and 12.27±1.53%, respectively). Prefreeze motility did not differ between cattle and buffalo bulls (64.97±1.08% Vs 67.11±0.89%, respectively) but post-thaw motility was significantly (P<0.01) higher in the buffalo (46.93± 1.39% Vs 37.70±1.32%). While incubation survival was higher in the cattle (18.04±1.16% Vs 10.96±0.89%). A fast cooling rate was found to be detrimental for cattle spermatozoa, whereas the post-thaw buffalo sperm motility deteriorated very quickly at 38°C. The influence of species-by-cooling rate interaction was significant (P<0.01) for post-thaw motility and survival rate, but the species-by-thawing or cooling-by-thawing interactions were not significant. These results suggest that a cooling rate of 2 hour either at 10°C or 28°C is essential for cattle semen. However, buffalo semen can be frozen successfully after 30 minutes of cooling at 10°C. A thawing temperature of 60°C yielded a higher sperm motility rate than 40°C. Thus, our findings can be applied under tropical conditions for the successful freezing-thawing of bovine semen provided conception rates are not affected adversely.