Changes in sperm quality and lipid composition during cryopreservation of boar semen

Egg yolks are commonly used in diluents in order to improve the freezability of semen. Two aspects of the role of lipids in boar semen freezability are reported in this article. The first one concerns the eventual exchanges of lipid components between the spermatozoa and the yolk-based diluent during cryopreservation. Two types of yolk have been considered as ingredients in diluents for cryopreservation: yolks with a standard fatty acid composition and yolks enriched in docosahexaenoic acid (DHA). The relation between lipid exchanges and the quality of fresh semen is considered. The other aspect concerns the possibility to enhance the freezability of boar spermatozoa by altering the plasma membranes under the influence of dietary fatty acids. Spermatozoa were damaged significantly by the cryopreservation cycle in all experiments. Spermatozoa with the best fresh quality had accumulated the largest quantity of lipids upon thawing. A general decrease in the proportion of polyunsaturated fatty acids was observed after thawing. The yolks enriched in n-3 fatty acids failed to improve the quality of sperm following cryopreservation. The proportion of DHA was significantly higher in spermatozoan phospholipids from thawed cells that had been in contact with n-3 yolks. A significant reduction in cholesterol was observed in spermatozoa after the cryopreservation cycle, which correlated with an increased number of acrosome-reacted cells and changes in the parameters of motility. The addition of 3% fish oil to the daily boar ration significantly increased the content of DHA (from 33 to 45% of the total fatty acids) in the spermatozoa. Ejaculate concentrations were significantly increased in the experimental group. DHA-enriched semen did not show improved freezability, at least not as assessed by in vitro parameters.