PURPOSE:To improve the development efficiency of fertilized egg during the period to return into the uterus of an adult cow by maturing and fertilizing a bovine egg in vitro and co-culturing the fertilized egg together with a trophoblast vesicle of bovine, thereby developing the bovine cell fertilized in vitro. CONSTITUTION:External development of a bovine egg fertilized in vitro is carried out by maturing and fertilizing a bovine egg in vitro and co-culturing the fertilized egg together with a trophoblast vesicle of bovine, thereby developing the bovine cell fertilized in vitro. As an alternative method, a fertilized bovine egg matured and fertilized in vitro is co-cultured together with a bovine trophoblast vesicle or bovine cumulus cell in a medium added with EDTA to develop the egg to a stage transplantable to the uterus of cow. The co-culture of the fertilized bovine egg is carried out in a medium having a bovine fetus serum concentration of 1-5%, to which EDTA is added and free from caloric source while keeping the oxygen concentration in the gaseous phase to 2-10%.
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