A simple osmotic stress test to predict boar sperm cryosurvival

This work was carried out to test whether viability of pig spermatozoa subjected to an osmotic test is correlated to sperm cryosurvival. Spermatozoa were cooled from 22 degrees C to -5 degrees C, aliquots were exposed to a series of hyperosmotic solutions (300-2100 mOsm/kg) for 15 min, immediately spermatozoa were re-warmed to 37 degrees C and isosmolarity was restored. Spermatozoa were cooled from 22 degrees C to -5 degrees C and one aliquot was exposed to the osmotic test while diluted spermatozoa were frozen-thawed. Plasma membrane-intact spermatozoa decreased as osmolarity increased (P < 0.0001), a further decreased (P < 0.0001) was observed when isotonicity was restored. Proportions of plasma membrane-intact and acrosome-intact cells from the osmotic test were no different from those after freeze-thawing: 36% vs. 35%, 80% vs. 80%, respectively. A significant correlation was found between the proportion of acrosome-intact cells after freeze-thawing and that from the osmotic test (r = 0.81, P <0.01). This test provides a useful and economical mean to predict in vitro boar sperm cryosurvival.