The current success of vitrifying in vitro produced porcine blastocysts is far behind that of other mammalian species. This chilling sensitivity is due to the high lipid content of porcine oocytes and embryos¹. There are numerous vitrification devices and solutions available, and studies suggest collapsing the blastocoele prior to vitrification improves survival². Few of these conditions have been examined using porcine embryos. The aim of this study was to determine the optimum conditions for vitrifying in vitro produced day 7 porcine embryos.

In experiment 1, embryos were vitrified using either superfine open-pulled straws (SOPS) or CryoLoop^TM. In experiment 2, embryos were vitrified in either Vitrolife media or a commonly used in-house media. In experiment 3, embryos were collapsed by micro-pipetting or needle puncture prior to vitrification. Survival of embryos was determined by the presence of a blastocoele cavity 24h post thaw. Data were subjected to ANOVA and Tukey’s test when differences were found.

The post-thaw survival of embryos vitrified in SOPS (36%) was similar to that of embryos vitrified in CryoLoop^TM (33%). Embryos vitrified in Vitrolife media had a similar re-expansion rate (42%) than that of embryos vitrified in in-house media (48%). The re-expansion rate of embryos that were collapsed via micro-pipetting (74%) did not differ from those that were punctured (82%) when freezing did not occur. However, the post-thaw survival rate of embryos that were collapsed prior to vitrification was lower than that of non-collapsed embryos (19% vs. 53%; P<0.05).

The findings show that the vitrification devices and media examined were equally effective for the vitrification of porcine embryos. Collapsing embryos prior to freezing decreased survival, which is inconsistent with the findings of studies in other species. This may be due to the extremely sensitive nature of porcine embryos, and the invasiveness of collapsing procedures.