Freezing Bovine Sperm with Egg Yolk

Bull spermatozoa were pellet frozen on dry ice in a TES buffer containing combinations of egg yolk and glycerol to determine which component of an extender afforded cryoprotection to the spermatozoa. Neither buffer nor buffer plus glycerol protected sperm cell motility in the absence of egg yolk, while sperm cells frozen in egg yolk buffer in the absence of glycerol had 24% postthaw motility (P < .05). Egg yolk was found to be the main cryoprotective agent, but there was a synergistic effect between glycerol and egg yolk in providing the greatest postthaw survival (40%) of sperm cells (P < .05). Purification of egg yolk to determine which fractions were affording protection was conducted using ultracentrifugation, Biogel fdtration and Sephadex fdtration. Purification procedures and agar gel electrophoresis indicated that a large lipoprotein complex could be isolated free of contaminating migrating proteins. The lipoprotein complex was the low density fraction (LDF) of egg yolk. In the absence of glycerol this complex protected motility of sperm cells during the" freezing process.