Freezability of Bovine Spermatozoa in Tris-Buffered Yolk Extenders Containing Different Levels of Tris, Sodium, Potassium and Calcium Ions

This study was designed to investigate the effect of different species of ions and osmotic pressure on survival of bull spermatozoa during freezing to --196 C. Replacing 20 to 80% of the Tris-buffered 20% yolk extender with isosmotic NaC1, KC1, or CaCI~ solutions was found to be harmful. Potassium was more harmful than Na or Ca at the highest level of replacement. When either 10 or 20% by volume of a 0.25 ~ Tris-buffered 1% yolk extender was replaced with isosmotic Na and K chloride and citrate salt solutions, survival of spermatozoa during freezing was not affected. Replacement of 50% or more of the Na citrate with K citrate in 1 and 20% yolk-citrate extenders reduced sperm cell survival before and after freezing. These results indicate that the optimmn levels of Na and K in extenders for freezing spermatozoa are less than the normal intracellular concentrations of these ions.