Effects of Method of Egg Yolk Addition and of Glycerol Equilibration Time upon Post-Thawing Motility and Metabolic Activity of Frozen Bull Semen

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Abstract
A semen sample from each of six Holstein and Guernsey bulls was used in a study to determine the effects of method of egg yolk addition to diluents and the glycerol equilibration time prior to freezing upon the quality of frozen semen stored for 2 weeks, 3 months, and 6 months at -79 C. Criteria for the quality of the thawed semen were the per cent of motile sperm, utilization of total reducing sugars, and lactic acid production. By all 3 semen quality criteria, there was some advantage in adding egg yolk to the glycerol as well as to the nonglycerol portions of the diluent, although the effect was not statistically significant. Six-, 12-, and 18-hr glycerol equilibration periods were superior (P<0.01) to a 2-hr equilibration period by all semen quality criteria. No interaction terms were of special significance.