This study was conducted to investigate the survival and hatching rates after refrozen-thawed bovine IVF blastocysts. The survival rates after refrozen-thawed bovine IVF blastocysts produced on day 7, day 8 and day 9, were 66.6%(16/24), 62.5%(15/24) and 65.3%(17/26), respectively. The survival and hatching rates after the first frozen-thawed bovine JVF blastocysts were 90.0%(27 /30) and 70.0%(21 /30), but in refrozen-thawed bovine IVF blastocysts were 66.2%(49 /74) and 45.9%(34 /74), respectively. The results of this study were suggest that refrozen-thawed bovine IVF embryos had survival ability.

This study was carried out to investigate the effect of equilibration time, sucrose concentration and age of embryo on survival and developmental rates of bovine IVF expanding blastocysts frozen-thawed by direct transfer method. The bovine oocytes were collected from 2~5mm follicles, matured for 20~24hrs in 5% incubator and then fertilized with frozen-thawed semen. Expanding blastocysts at day 7, 8, 9, 10 and 11 after IVF were frozen in 1.8M ethylene glycol(EG). Survival and hatching rates of frozen-thawed IVF embryos were examined. The results were as follow ; Survival and hatching rate of TVF expanding blastocysts after 10, 20, 3Omin exposure in 1.8M EG were 100,0,90.9, 47.1, 85.0, 75.0 and 62.5% respectively. Survival rates of IVF expanding blastocysts frozen with 1.8M EG and various concentration(0, 0.25, 0.5, 1M) of sucrose were 73.3, 25. 0, 16.7, 9.1% respectively. Survival and hatching rates of IVF expanding blastocysts frozen-thawed according to age of embryo(Day 7, 8, 9,10, 11) were 86.1, 84.8, 79.3, 61.4, 51.3, 74.2, 76.9, 71.7, 63.0 and 65.0% respectively. In conclusion, the age of the embryo(Day 7, 8) is very important for the successful freezing of IVF bovine embryos and 1.8M ethylene glycol not containing sucrose may be effective cryoprotectant for direct transfer method.