Plasma membrane changes during the liquid storage of boar spermatozoa: a comparison of methods

Studies were performed on boar semen routinely used at the local artificial insemination (AI) centre. The semen was stored in a Safe Cell Plus commercial extender at 17 degrees C for nine days. The aim of our research was focused on changes in sperm plasma membrane integrity. The integrity of the sperm plasma membrane and acrosome as well as sperm motility decreased after dilution and during storage of the semen. The highest percentage of live sperm was identified by the eosin-nigrosin method, a lower percentage by the SYBR-14/PI test, and the lowest percentage of live cells was discovered by the hypoosmotic swelling (HOS) test (P < 0.01). There were significant differences between the results of staining methods and sperm motility (P < 0.01). No significant differences were found between the HOS test results and sperm motility. The plasma membrane integrity parameters positively correlated (P < 0.001) with each other and with sperm motility but negatively with aspartate aminotransferase activity. Our findings confirmed that the boar sperm aging changes, which increased during liquid semen preservation, were connected with the loss of function and integrity of the sperm plasma membrane. The employed complementary tests are comprehensive indicators of sperm membrane integrity during long-term semen preservation, and they can help establish the actual number of 'healthy' cells. The assays may be used in AI laboratories and should be incorporated into the routine of semen analysis.