Use of polyvinyl alcohol as a chemically defined compound in egg yolk-free extender for dog sperm cryopreservation

The objectives of this study were to investigate the effects of polyvinyl alcohol (PVA) as a chemically defined compound in egg yolk (EY)-free extender by determining the appropriate concentration of PVA and the effect of pH adjustment in EY-free PVA extenders on dog spermatozoa. Spermatozoa (1 × 10⁸  cells/ml) were frozen with EY-free extenders supplemented with 0 (control), 0.025, 0.05, 0.1, 0.2 or 0.3 g/100 ml PVA. Sperm progressive motility (PM) was assessed immediately after thawing (IAT) and post-thaw incubation (PTI), while viability, acrosome integrity and reactive oxygen species (ROS) levels were evaluated after PTI. Additionally, spermatozoa were frozen using EY-free PVA extenders before pH adjustment (6.45) and after adjustment of pH (6.85). Viability, PM, ROS and gene expression (BCL2 and SMCP) were assessed. Supplementation with 0.05 g/100 ml or more PVA significantly increased PM compared to the control group in the IAT and PTI. Post-thaw incubation significantly increased sperm motility in all groups. The acrosome integrity in all PVA groups was higher (p < .05) than the control without an effect on ROS and viability. Adjustment of the pH to 6.85 improved (p < .05) sperm PM compared to the non-adjusted groups without affecting viability, ROS or expression of BCL2 and SMCP. We suggest that PVA supplementation in EY-free Tris extenders can effectively protect dog spermatozoa during freezing and can maintain higher motility and acrosome integrity. Adjustment of pH in EY-free PVA extenders can improve post-thaw sperm motility. Therefore, PVA can be used as a compound in EY-free extender for the cryopreservation of dog spermatozoa.