In Vitro Development Potentiality of Expanded Bovine Blastocysts Subsequent to Cryotop Vitrification

Abstract

Embryo cryopreservation is a promising area of study in the field of reproductive research. One of the issues that have recently arisen is the discovery that the growing ability of embryos after cryopreservation varies depending on the culture period of the embryo prior to its cryopreservation. Therefore, the present study was designed to explore the in vitro development potentiality of bovine embryos at day 7 and day 8, as well as their survivability and hatchability after Cryotop vitrification. The blastocyst rate at day 8 (28.1%) was higher than that of day 7 (19.1%). Grade 1 (G1) and grade 2 (G2) expanded blastocysts at day 7 and day 8 were vitrified by Cryotop device using 20% (v/v) DMSO, 20% (v/v) EG and 0.5M. Except for the G2 expanded blastocysts at day 8, we found that the survival rates of vitrified G1 and G2 expanded blastocysts were not significantly different from the control group in both day 7 and day 8. However, the day 7 vitrified embryos showed superior rates of hatchability than those of day 8. In a curve estimation of correlation regressions, the hatching rate of day 7 G1 expanded blastocysts at 48 h showed a strong correlation (R²=0.914) with their survival rate. Therefore, we concluded that the day 7 culture period is the most suitable for vitrification of IVF derived blastocysts.