A simplified method for freezing mouse embryos

Mouse oviducts containing eight-cell embryos were frozen to ?196 °C in 1.45 m DMSO. The cooling rate was 0.3 °C/min and thawing occurred at 3 °C/min. Dilution of DMSO took place either before or after flushing of the thawed oviducts. The yield of intact embryos was higher in the second group.In one particular series involving 21 donor mice (natural ovulation) 88 recovered embryos were transferred to the oviducts of recently mated pseudopregnant mice without prior in vitro culture to the blastocyst stage. Fifty-five live young were born.It is concluded that the freezing of embryos in the oviduct is a reliable method for establishing an embryo bank. Handling and collection of isolated embryos is not required and a large amount of material can be frozen at once. In vitro culturing of embryos is not required immediately after thawing in order to obtain a high yield of live young.