The improving effect of reduced glutathione on boar sperm cryotolerance is related with the intrinsic ejaculate freezability

Reduced glutathione (GSH) improves boar sperm cryosurvival and fertilising ability when added to freezing extenders. Poor freezability ejaculates (PFE) are known to present lower resistance than good freezability ejaculates (GFE) to cryopreservation procedures. So far, no study has evaluated whether the ability of GSH to counteract the cryopreservation-induced injuries depends on ejaculate freezability (i.e. GFE vs. PFE). For this reason, thirty boar ejaculates were divided into three equal volume fractions and cryopreserved with or without GSH at a final concentration of either 2 or 5 mM in freezing media. Before and after freeze–thawing, sperm quality was evaluated through analysis of viability, motility, integrity of outer acrosome membrane, ROS levels, integrity of nucleoprotein structure, and DNA fragmentation. Ejaculates were classified into two groups (GFE or PFE) according to their post-thaw sperm motility and viability assessments in negative control (GSH 0 mM), after running cluster analyses. Values of each sperm parameter were then compared between treatments (GSH 0 mM, GSH 2 mM, GSH 5 mM) and freezability groups (GFE, PFE). In the case of GFE, GSH significantly improved boar sperm cryotolerance, without differences between 2 and 5 mM. In contrast, PFE freezability was significantly increased when supplemented with 5 mM GSH, but not when supplemented with 2 mM GSH. In conclusion, PFE need a higher concentration of GSH than GFE to improve their cryotolerance.