43 NEW METHOD FOR ONE-STEP WARMING/IN-STRAW CRYOPROTECTANT DILUTION FOR IN VITRO-PRODUCED BOVINE BLASTOCYSTS AFTER VITRIFICATION WITH THE CRYOLOGIC VITRIFICATION METHOD

Abstract

Vitrification is considered an alternative to slow-rate freezing to cryopreserve in vitro-produced (IVP) bovine embryos. However, the use of vitrified IVP embryos for embryo transfer under field conditions is difficult because of the requirements of the current thawing protocols. The objective of this study was to develop a simple one-step warming/in-straw cryoprotectant dilution procedure for IVP bovine blastocysts that were vitrified using the cryologic vitrification method. In this study, 109 Day-7 IVP blastocysts were subjected to vitrification using the conventional fibreplugs (groups of 5 embryos were loaded in 3 mL of vitrification medium). Warming was performed in one-step in MS1 (0.25 M sucrose in BV = TCM 199-Hepes + 20% FCS) either using a 4-well plate for 5 min (control group) or in a new system that allowed in-straw cryoprotectant dilution designed to avoid losses of embryos and to maintain the temperature required during this procedure. This new system is composed of an adaptor with a wider opening that is coupled to the French straw and a heated metal chamber to protect and keep the straw at 41°C. Warmed embryos were washed and subsequently cultured in mSOFaaci + 6 gL^–1 BSA + 10% FCS for 48 h. Re-expansion (at 2, 24, and 48 h) and hatching rates (at 24 and 48 h) were recorded. Data were analysed by ANOVA and are presented as LSM ± standard error. Embryo survival rates of embryos warmed by the one-step warming/in-straw cryoprotectant dilution procedure did not differ from the control group (see Table 1). These results suggest that the cryologic vitrification method combined with our warming system for in-straw cryoprotectant dilution may be used for direct embryo transfer under field conditions.

Table 1.  Embryo survival rates of in vitro-produced embryos vitrified by the cryologic vitrification method and warmed by the new one-step warming/in-straw cryoprotectant dilution procedure

This study received grant support: INIA-RTA 2011–0090 and FEDER. M. Muñoz was supported by grant MICINN-RYC08-03454, and B. Trigal by a grant from Cajastur. The authors are members of the COST Action FA1201 Epiconcept.