Diluents for Bovine Semen. XII. Fertility and Motility of Spermatozoa in Skimmilk with Various Levels of Glycerol and Methods of Glycerolization

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Abstract
Laboratory studies showed that the beneficial effect of glycerol on the maintenance of sperm motility in skimmilk diluent during 5[degree]C storage was related both to level and method of glycerol addition. Optimum livability was obtained with 5% glycerol and when the glycerol-containing fraction was added stepwise to the partially diluted semen at 5[degree]C. Direct addition of semen to completely formulated skimmilk- 13% glycerol diluent at room temperature significantly reduced sperm livability as compared to that in partially diluted semen gly-cerolated in a stepwise fashion at 5[degree]C. Even when glycerol level in the complete diluent was lowered from 13 to 15%, and the semen added at room temperature, livability during 14 days of storage was slightly better in the skimmilk-13% glycerol control samples glycerolated stepwise at 5[degree]C. Dilution at room temperature into completely formulated skimmilk-glycerol diluents containing more than 5% glycerol also resulted in abnormal sperm motility (circular or backward movement). In skimmilk-glycerol diluents containing 5, 10, and 20% glycerol, livability was superior (P<0.01) when the glycerol fraction was added to the partially diluted semen at 5[degree]C in 3 steps rather than all at once at 5[degree]C or dropwise during the cooling process. Irrespective of glycerolization method, there was a highly significant increase in mean livability with each decrease in glycerol level. However, based on a split-sample field trial involving 9606 first inseminations, fertility on any of the 4 days of use was not significantly different in skimmilk-diluted semen containing 5% rather than 10% glycerol.