A pilot study: Comparison of pregnancy rates from vitrified Jersey embryos utilizing direct transfer methods with pregnancy rates of Jersey and Holstein embryos frozen in ethylene glycol or glycerol by slow-cooling methods

Abstract

It has been previously reported that pregnancy rates from frozen Jersey embryos are lower than pregnancy rates from other breeds of cattle. This study incorporated 1.5M ethylene glycol or 1.4M glycerol as cryoprotectants and utilized slow-cooling freeze programs. The present study was undertaken to determine if the vitrification of Jersey embryos in 0.25 cc straws could result in a more favorable pregnancy rate than previously reported. In addition, an in-straw dilution of cryoprotectants with resulting direct transfer (DT) of embryos was evaluated to determine if this methodology is compatible with vitrification processes. Ten superovulations of nine Jersey donor cows yielded 50 embryos that were vitrified and subsequently thawed and transferred into suitable recipients using DT methodology. The resulting pregnancy rate (28%) is numerically lower than retrospective pregnancy rates achieved from Jersey embryos slow-cooled in 1.4M glycerol or 1.5M ethylene glycol (46.2% and 39.9% respectively). However, two Jersey donors achieved reasonable pregnancy rates with their vitrified embryos (50%). This study has shown that average pregnancy rates of vitrified Jersey embryos utilizing DT methodology is numerically lower than average pregnancy rates of conventional, slow-cooled embryos. However, due to the wide range of pregnancy rates in this study, individual donor cows may have different cryotolerances to this vitrification method. Further modifications of vitrification systems utilizing DT methods may eventually improve overall pregnancy rates of frozen Jersey embryos.