AN IN VITRO ASSESSMENT OF THE VALUE OF SUCROSE SUPPLEMENTATION TO WARMING MEDIA FOR THE VITRIFICATION OF BOVINE EMBRYOS

BACKGROUND: In order to thaw slow-cooled bovine embryos it is standard practice to draw out permeating cryoprotectants by passing embryos through successively decreasing osmotic solutions. However, recently it has been suggested that sucrose may not be needed in the warming media. OBJECTIVE: The aim of this experiment was to compare the effect of warming media prepared with or without the inclusion of sucrose on the survival and hatching capacity of vitrified in vitro-derived bovine embryos. MATERIALS AND METHODS: Expanded blastocysts were produced in vitro and vitrified. Vitrified embryos were warmed either successively through 0.5, 0.3 and 0.2 M sucrose solutions (`stepwise')-, or by placing directly into the blastocyst solution without the addition of sucrose ('direct'). A total of 93 expanded blastocysts were assigned randomly to two treatment groups, respectively. RESULTS: The re-expansion rates of vitrified embryos warmed after 24h in vitro culture were similar between the two groups (46/46, 100%; 46/47, 97.9%). From those vitrified embryos that expanded at 24 h there was also no significant difference in hatching rates after 48 h in vitro culture (42/46, 91.3%; 40/46, 87.0%). CONCLUSION: The findings indicate that stepwise warming through sucrose solutions is not required for continued embryo development. Hence, a more time-efficient warming method for vitrified embryos may be followed when conducting cattle embryo transfers.