Time of early cleavage affects the developmental potential of feline preimplantation embryos in vitro.

The study compared developmental competence of embryos, based on the timing of the first cleavage and morula formation, with their subsequent ability to reach the blastocyst stage and the resulting blastocyst morphology and quality. Cleaved embryos were separated at 18 hours post insemination (hpi), 24 hpi, and 30 hpi and then cultured in droplets to follow the individual embryo development. The significantly higher percentage of the blastocyst formation was noted in the group I of embryos cleaving within less than 18 hpi (12.7%) compared with the group II cleaving within 18 to 24 hpi (10.7%), None of the late-cleaving embryos (group III >24-30 hpi) reached blastocyst stage in our experiment. Interestingly, the hatching ability was similar regardless the time of the first cleavage (I: <18 hpi; 6.4% and II: 18-24 hpi; 5.4%). The ability to hatch was correlated with the time of morula formation; only embryos that reached morula on Day 4 or Day 5 were able to develop into hatching blastocyst (8.4% and 3.3%, respectively). The differential cell staining revealed significantly more blastomeres in blastocysts obtained from embryos cleaving within 18 to 24 hpi than the blastocysts obtained from embryos cleaving less than 18 hpi (188.6 ± 21.9 vs. 129.3 ± 16). Embryos cleaving within 18 to 24 hpi also demonstrated the higher number and percentage of embryoblast cells (97.2 ± 12.6, 51.6 ± 2.9 vs. 46.6 ± 9, 36.3 ± 6.6). The presented results confirmed the association among the onset of the first cleavage, time reaching morula, and subsequent blastocyst formation and quality.