Development of bovine embryos produced in vitro from the one-cell to the blastocyst stage in serum-free oviduct-conditioned medium was investigated for 8 days consecutively by time-lapse cinematography. Three movies were analysed (130 embryos). The following observations were made. (1) Development under cine-recording conditions was similar to that in a classical incubator. (2) The highest proportion of embryos at the two-cell, three–four-cell, five–eight-cell, 9–16-cell, morula and blastocyst stages were recorded at 34, 46, 61, 115, 149 and 192 h after insemination, respectively. Cleavage asynchrony between blastomeres within individual embryos started at the two-cell stage. (3) The duration of the first three cell cycles was 35 h, 14 h and 11–62 h, respectively. (4) Detailed analysis of 13 embryos revealed that developmental arrest ('Lag-phase') occurred at the four-cell (1 of 13), five-cell (2 of 13), six-cell (3 of 13), seven-cell (3 of 13) or eight-cell stage (4 of 13); this phase lasted about 59 h. Embryos arrested at the eight-cell stage developed into morula–blastocysts (3 of 4) at a higher rate than did those arrested at earlier stages (2 of 9). (5) The faster the embryos cleaved into early stages (two-cell, three–four-cell and five–eight-cell), the higher the probability that they developed into morula–blastocyst: 70% of the embryos reaching the two-cell stage before 30–31 h after insemination developed into morula–blastocyst. We suggest that the lag-phase as well as the link between early cleavage kinetics and further development could be related to the transcriptional activity of the embryo at about the 5–8-cell stage.
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