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

Abstract

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[degree]C. Replacing 20 to 80% of the Tris-buffered 20% yolk extender with isosmotic NaCl, KC1, or CaCl2 solutions was found to be harmful. K was more harmful than Na or Ca at the highest level of replacement. When either 10 or 20% by volume of a 0.25 M 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 optimum levels of Na and K in extenders for freezing spermatozoa are less than the normal intracellular concentrations of these ions. Osmotic pressure of a 0.25 M Tris-buffered 20% egg yolk extender (freezing point depression, 0.55[degree]C) was increased by adding NaCl, KC1, and CaCl2 singly and in all combinations. As the osmotic pressure increased, motility of the spermatozoa after freezing declined in a linear manner, regardless of the tonicity contributed by each cation studied.