Influence of Percent Egg Yolk during Cooling and Freezing on Survival of Bovine Spermatozoa

The influence of percent egg yolk during cooling from 37 to 5C on ability of sperm to withstand subsequent freezing was studied with semen from each of eight bulls. Treatments were arranged factorially and included .5, 1, 2, 4, 8, 16, and 32% egg yolk, cooling times of .5, 1, 2, and 4h, and freezing in ampules and straws. Percent egg yolk did not influence motility or percent intact acrosomes when semen was frozen in ampules. For sperm in straws, both post-thaw percentages of motile sperm and intact acrosomes were similar for sperm cooled with .5, 1, 2, 4, or 8% egg yolk and greater than with 16 or 32% egg yolk. Optimal egg yolk during cooling was not dependent upon rate of cooling, regardless of how semen was packaged for freezing. The influence of percent egg yolk during freezing was investigated in a second study. Treatments included eight bulls; 1, 2, 4, 8, 16, and 32% egg yolk; freezing times from +5 to −130C of 3.5, 20, and 40min; and freezing in ampules or straws. Optimal egg yolk during freezing in either ampules or straws was independent of the rate of freezing. For sperm frozen in ampules, differences in motility or the percent intact acrosomes due to egg yolk were small. However, the use of only 1 or 2% egg yolk depressed motility whereas 16 or 32% egg yolk decreased the percentage of intact acrosomes. Thus, extremely high or low egg yolk should be avoided. For sperm in straws, survival was optimal when the extended semen contained 4 to 32% egg yolk during freezing.