At present embryos are frozen for long-term preservation. But this method is not easy to carry out because of the complexity of the equipment and procedure required and the many problems yet to be solved. The authors studied the possibility of unfrozen low-temperature preservation of embryos for a short period by keeping them at 5-8 °C. As a result, it was found that embryos at the 8-16 cell stage were well preserved in serum-added geratine solution. The optimal serum concentration was 33.3%, and the addition of gelatine had a favorable effect. When rabbit embryos at the morula stage were preserved in rabbit oviducts, they survived up to 7 days in nearly all the cases, while mouse embryos preserved in rabbit oviducts were not viable. When rabbit embryos were preserved in blood vessels, viable embryos were obtained up to 5 days from more than half the cases. These embryos were transfered, and they were proved normal embryos because they yield young. The above-mentioned findings indicated that this method could be put to practical use with detailed studies of the oval stage, medium, and enviroment optimal for embryo preservation.
