Freezing of Bovine Semen. II. Effect of Milk Solids Level, Glycerol Level, and Fructose on Freezability of Bull Spermatozoa in Reconstituted and Fresh Skimmilk Diluents1,2,3

Abstract

This investigation revealed that the level of glycerol required for optimum spermatozoan freezability was related to the total solids content of skimmilk diluents, and that 1.25% added fructose improved the post-thawing motility of spermatozoa frozen in reconstituted skimmilk. Reconstituted skimmilk gave optimum spermatozoan survival when the glycerol percentage by volume equalled the total solids l~ercentage by weight, and when both were 9 or 11%. In fresh skimmilk containing 9% solids, 11% glycerol was significantly better than 9 or 13%, Editor. A recent report from this station (8) cited levels of glycerol found by various workers to give optimum freezability of bovine spermatozoa in heated fresh skimmilk diluent. In egg yolk-citrate diluent, the optinmm glycerol level for freezing bull semen has been found to be dependent both upon the concentration of egg yolk (10) and upon the concentration of sodium citrate (3) in the diluent. Saaeke and Almquist (9) observed that altering the total solids content of skimmilk from 9 to 11% resulted in significantly decreased spermatozoan livability at +5 ° C. The fortification of skimmilk used for human consumption to approximately 10.5% total solids is a common commercial practice. Tlms, it appears that the level of glycerol required for optimum spermatozoan freezability in skimmilk diluent may be influenced by the total solids content of the milk. The inclusion of fructose in heated skimmilk and egg yolk-citrate diluents has been found to improve spermatozoan freezability (1, 7, 8). Reconstituted (Instant Pet) nonfat dry milk solids were found by Johnson et al. (4) to provide a satisfactory diluent for storing bovine spermatozoa at +5 ° C. Use of powdered milk diluent for freezing semen would be especially advantageous in areas where good-quality fresh milk is difficult, or impossible, to obtain. The present study was undertaken to determine, (a) if the level of glycerol required for optimum spermatozoan freezability is related to the total solids