New thermal stress test to assess the viability of cryopreserved boar sperm.

A new, rapid, thermal stress test for assessing the viability of boar semen, requiring only 45 min of incubation at 42.5 degrees C, was developed and compared with a widely used stress test of 180 min incubation at 37 degrees C. The shorter procedure was found to have the same discriminatory ability as the standard test in assessing the effects of freezing conditions on the percentage of spermatozoa remaining motile. Neither test was able to show differences in the kinetic rating of motile sperm after freezing in relation to the glycerol concentration present during freezing. However, the new test had a greater ability to distinguish the effects of different concentrations of glycerol, over the range of 0 to 6%, and to reveal different degrees of acrosomal damage sustained during freezing. The longer procedure was unable to distinguish among glycerol concentrations from 0 to 4% with respect to acrosomal damage and produced an overall lower proportion of sperm having a normal apical ridge. The new thermal stress test thus has the advantages of greater sensitivity and more rapid execution over the test hitherto in widespread use.