Freezing Bovine Semen. I. Techniques for Freezing Bovine Spermatozoa in Milk Diluents

Abstract

Effects of level of glycerol and method of adding it, equilibration time, and addition of sugars to milk diluents, on the survival of spermatozoa after freezing, were studied. Heated and cysteine -treated homogenized milk and skimmilk diluents gave survival rates after freezing equal to those obtained with egg yolk-citrate diluent. With homogenized milk, 10% glycerol by volume gave slightly higher survival rates than 7 or 13% glycerol. With skimmilk, 10 to 13% was required, whereas with egg yolk-citrate, better results were obtained with 7 and 10% glycerol. Spermatozoa frozen in milk diluents maintained a higher percentage motility after thawing and storage at + 5[degree]C than spermatozoa frozen in egg yolk-citrate. The stepwise addition of glycerol to semen diluted and frozen in heated skimmilk gave slightly better post-thawing motility than adding glycerol all at one time. In skimmilk diluent, prefreezing glycerol equilibration periods of 30 minutes and 4 hours resulted in spermatozoan survival equal to or better than 18 hours. Equilibration time was not related to the level of glycerol present in the diluent. The addition of 1.25% fructose to a skimmilk diluent resulted in a significant increase in freezability of bull spermatozoa, as compared to untreated controls. However, the addition of sugar had no effect on equilibration period or level of glycerol needed for optimum freezability. The addition of sugar resulted in higher percentages of motile spermatozoa following storage at -79[degree]C for ten days than samples without added sugar.