Osmotic Pressure and pH Effects on Survival of Frozen Bovine Spermatozoa

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Abstract
Semen from 10 bulls was extended in egg yolk extenders buffered with 5 concentrations of Tris adjusted to four pH levels, and containing 2 levels of glycerol, to study their interactions during semen freezing. Spermatozoa in these 40 media (5x4x2) were equilibrated for 1.5 and 6.0 hr. frozen at 0.8 and 3.0[degree]C/min. in the critical range, and stored 7 days at -196[degree]C. Duplicate estimates of the percentage of motile spermatozoa made immediately after thawing (6,400 observations) indicated that the freezing rate and equilibration time had little effect on survival. The percentages of motile spermatozoa for 6.4 and 8.8% glycerol levels were 30 and 28, for the 0.15, 0.20, 0.25, 0.30, and 0.35 [image] Tris-buffered yolk extenders 37, 40, 37, 28, and 5; and for the pH''s of 6.0, 6.5, 7.0 and 7.5, 25, 29, 30, and 31, respectively. These effects were statistically significant (P< .005). Several main factors interacted in opposing ways, thus reducing their overall differences. The highest percentage of motile spermatozoa was observed in the extender adjusted to pH 6.50 containing 0.20 [image] Tris, 6.4% glycerol and 1% fructose; motility averaged over the 2 equilibration periods was 43% upon thawing and 33% after an additional storage period of 24 hr. at 5[degree]C. This extender without glycerol was slightly hyperosmotic to sperm, as evidenced by a freezing point depression of 0.62[degree]C.

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