Effect of Glycerol on Lactic Acid Production by Bull Spermatozoa Diluted in Heated Skimmilk and Egg Yolk–Citrate

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Abstract
An experiment was designed to compare lactic acid production by bull spermatozoa in heated fresh skimmilk and 1:4 egg yolk-citrate diluents, with no additives, with 10% glycerol by volume, with 1.25% fructose by weight, and with 1.25% fructose plus 10% glycerol. A total of 3 replicates were conducted. Lactic acid accumulation in the presence of 10% glycerol was approximately 25% less (P<0.01) than the average for 3 other diluent treatments. The addition of fructose alone, or with glycerol, did not significantly change lactic acid production in either diluent. Spermatozoan motility was approximately equal in all diluent combinations initially (average 51%) and was not significantly reduced after 3 hours of incubation (average 48%). Whether additives were present or not, spermatozoa incubated in egg yolk-citrate produced highly significantly (P<0.01) greater amounts of lactic acid than did those in skimmilk diluent. Addition of glycerol to either skimmilk or yolk-citrate diluent resulted in approximately the same percentage depression in lactic acid production. However, the amount of lactic acid produced by sperm in yolk-citrate-glycerol was similar to that produced in milk without glycerol or milk-fructose. These results show that glycerol has a definitely depressing effect on lactic acid production by spermatozoa diluted in commonly used semen diluents. Although sugar utilization was not determined, reduced lactic acid accumulation indicates that glycerol possibly depresses glycolysis by bull spermatozoa. This may be related in part to the maintenance of higher fertility on the 3d and 4th days after collection, with semen diluted in milk-glycerol, than that found for semen diluted in milk without glycerol.