Treating sperm with cholesterol-loaded cyclodextrins (CLC) improves the cryosurvival of the sperm of different cold-shock sensitive species. However, the response of boar sperm to this treatment is not fully understood. The aim of this study was to determine how CLC and methyl-β-cyclodextrin (MβCD, not loaded with cholesterol) affect the parameters for boar sperm functionality, including sperm osmotic resistance, and the ability of the sperm to capacitate and to penetrate the sow's immature oocytes in vitro. Samples treated with CLC or MβCD prior to freezing exhibited similar percentages of motile sperm, live sperm and sperm with intact acrosomes as the control samples (P>0.05). In addition, these treatments did not alter the response of the boar sperm to capacitating conditions. However, when compared to the controls and the MβCD-treated samples, the CLC-treated sperm maintained greater percentages of motile sperm and live sperm in a wide range of osmotic solutions including hypo- (50, 75 and 150 mOsm/kg) and hyper-osmotic (600, 800 mOsm/kg) conditions (P<0.05). In addition, the CLC-treated sperm exhibited greater oocyte penetration ability than the control and the MβCD-treated sperm (P<0.0001). In conclusion, the pre-freezing treatment of boar sperm with CLC does not alter the ability of the sperm to respond to capacitating conditions. Despite not increasing the cryosurvival of the sperm, this treatment widens the sperm osmotic tolerance limits and enhances the in vitro sperm fertilising ability.
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