Modified hypoosmotic swelling test for the assessment of boar and bull sperm sensitivity to cryopreservation

Abstract

Routine methods for the evaluation of sperm quality are not sufficiently useful to determine the sensitivity of sperm cells to cold shock. The aim of our preliminary study was to determine whether the sperm plasma membrane integrity evaluated by modified hypoosmotic swelling test based on simple hypoosmotic swelling test (HOS test) and eosin-nigrosin staining could be helpful in predicting the degree of boar sperm survivability during semen cryopreservation. Ejaculates collected from 24 boars and 20 bulls were used in the experiment. Fresh ejaculates were evaluated by routine sperm analysis and a modified HOS test, and subsequently frozen. Sperm cryosurvivability was defined as the percentage of motile spermatozoa that survived the freezing process. A higher percentage of sperm was recovered after the thawing of semen with a higher percentage of HOS-positive and eosin-negative sperm (P < 0.01). Both indicators were found to be correlated (r = 0.707 and r = 0.705, respectively; P < 0.01). Moreover, the percentage of HOS-positive and eosin-negative sperm was similar to the percentage of viable sperm after thawing as determined by traditional eosin-nigrosin staining in boars (50.90 ± 9.88% and 49.31 ± 11.63%, respectively) and bulls (55.91 ± 10.34% and 55.63 ± 6.64%, respectively) and both indicators showed a positive correlation (r = 0.558 and r = 0.504, respectively; P < 0.05). In conclusion, based on the obtained results, we can assume that the modified HOS test can detect differences in sperm membrane resistance which allows assessment of semen quality from the perspective of its further use, e.g. cryopreservation.