Freezing of Bovine Semen. II. Effect of Milk Solids Level, Glycerol Level, and Fructose on Freezability of Bull Spermatozoa in Reconstituted and Fresh Skimmilk Diluents

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Abstract
The relationship between total milk solids and glycerol levels was studied in heated, reconstituted, Instant Pet nonfat dry milk solids (NFDMS) and in heated fresh skim-milk diluents. In both diluents, highly significant interactions (P< 0.01) were found between the solids and glycerol levels required for optimum spermatozoan motility after thawing from -79[degree]C. With NFDMS, optimum motility was obtained when the percentage of glycerol (by volume) was equal to the percentage of total solids (by weight) and when both were 9 or 11%. With fresh skimmilk, however, maximum freezability was not attained until the glycerol level exceeded the total solids level. When fresh skimmilk contained 9% solids, 11% glycerol was significantly better than 9 or 13%. With fresh skimmilk fortified to 11% solids with condensed skimmilk, the use of either 11 or 13% glycerol gave significantly better results than 9%. Comparable freezability was obtained in both diluents with either 9 or 11% milk solids only if the proper level of glycerol was used. The addition of 1.25% fructose to NFDMS diluents resulted in a highly significant increase in post-thawing motility and reduced the variation among ejaculates in spermatozoan survival. From these studies, heated reconstituted NFDMS diluent is equally as good as heated fresh skimmilk diluent for freezing bull spermatozoa.