Comparison of efficiency of open pulled straw (OPS) and Cryotop vitrification for cryopreservation of in vitro matured pig oocytes.

During the past few years vitrification has been acknowledged as a viable alternative to traditional slow-rate freezing in both animal and human embryology. However, few data are available regarding the comparative efficiency of published and commercially available vitrification methods. The purpose of our work was to compare the OPS and Cryotop technology for cryopreservation of porcine in vitro matured oocytes. In a 2 x 2 factorial experiment, OPS and Cryotop devices and solutions were used for vitrification and warming. Two hours after warming oocytes were parthenogenetically activated and cultured in vitro. In 6 replicates a total of 1153 oocytes were vitrified. The cleavage rate after vitrification with Cryotop device and Cryotop solution (34.7%) were higher than those after vitrification with Cryotop device and OPS solution, or OPS device with both OPS and Cryotop solution (11.5, 5.1 and 11.3%, respectively). Further embryo development has shown a similar difference: Cryotop device applied with Cryotop solution resulted in 11.6% blastocyst/oocyte rates, higher than those achieved with Cryotop device and OPS solutions, or OPS device with both Cryotop and OPS solution (1.6, 1,65 and 0.6%, respectively). Our results indicate that for cryopreservation of some highly sensitive biological specimen including porcine oocytes Cryotop vitrification is superior to the OPS technique.