Continuous observation of rabbit preimplantation embryos in vitro by using a culture device connected to a microscope

We developed a compact culture device that maintains developing embryos in vitro under constant temperature and CO(2) concentration. Using this device, we cultured rabbit embryos from the pronuclear stage to the hatched blastocyst stage and recorded their development digitally for 7 d. Recorded images were converted to a movie, and the developmental movement of individual embryos was analyzed. With this culture system, we can observe embryonic development in a suitable environment continuously for several days; similar long-term observation is not possible in the conventional system. The proportion of embryos that developed from the pronuclear stage to the blastocyst stage was the same in the new system (73.1%; 38 of 52) as in the conventional (control) system (77.6%; 38 of 49). Compaction of embryos occurred from the 8-cell to the morula stage at 32.5 +/- 0.71 h after insemination. The time of blastocyst formation (77.2 +/- 3.2 h after insemination) varied somewhat between embryos. Average hatching time was 98.7 +/- 4.4 h after mating. Therefore, the cleavage, blastomere movement, and hatching processes of blastocysts can be followed clearly and recorded by using this new culture system.