Large batch freezing of bull semen: effect of time of freezing and fructose on fertility.

Large-scale batch freezing of bull semen should be done in a processing schedule that yields the highest fertility and when it can be fitted efficiently into the work schedule. Conflicting reports have appeared on survival and fertility of bull sperm frozen within a few hours of semen collection or on the next day. To study this problem, a factorially arranged experiment with semen from 10 bulls was conducted, comparing whole milk-glycerol semen extender with and without fructose, and semen frozen in 0.5-ml straws after 4 versus 18 h of equilibration at 5 degrees C. Both fructose and 18 h of equilibration resulted in a small but significant improvement in freeze-thaw survival of sperm. A field trial followed with replicated semen collections from nine bulls processed in a whole milk-glycerol control extender frozen after 4 h of equilibration versus the addition of 1.25% (wt/vol) fructose to whole milk glycerol divided to freeze sperm after 4 and 28 h of equilibration. Semen from these bulls was used to inseminate 14,775 first-service cows. The 56-d nonreturn rates obtained for these three treatments were 74.7, 74.3, and 73.9%, respectively. As there was no difference in fertility, it would appear that programs to freeze sperm in whole milk extenders the same day of collection or the day after semen collection should yield equivalent results.