Time-lapse in vitro cultivation of cattle embryos to the blastocyst stage

The aim of the study is to apply time-lapse observation to monitor the development of bovine embryos in vitro, and to analyze the prognostic potential of morphokinetic parameters of cleavage as a criterion for assessing the competence of the embryo to form a blastocyst. The study was performed on postmortem material; oocyte maturation, fertilization and cultivation of bovine embryos to the blastocyst stage occurred in vitro. The potential ability of the embryo to form a good quality expanded blastocyst can be determined based on the temporal and morphological characteristics of the first and three subsequent divisions of the embryo (from the zygote to the formation of the 4-cell stage). If the embryo division fits into the time intervals we have defined and there are no signs of abnormal multipolar or unequal zygote cleavage, the embryo develops more effectively and more often reaches the blastocyst stage: the first division of the embryo should occur in (27.77 ± 0.28) h after oocyte fertilization; the duration from the moment of formation of the cleavage furrow to the formation of a two-cell embryo should be no more than (0.38 ± 0.05) h; the second and third divisions with the formation of a 4-cell embryo should occur no later than (36.58 ± 0.27) and (37.77 ± 0.32) h after fertilization. Embryos whose development did not fit into the specified time parameters, as a rule, stopped at different stages of development, not developing to the blastocyst stage. Multipolar division into three or more blastomeres and unequal division into blastomeres of different sizes were, according to our data, negative prognostic signs of early embryogenesis. Multipolar division occurred with a frequency of 29.71 % in embryos that did not form a blastocyst, and only 9.26 % in embryos that developed to the blastocyst stage, unequal cleavage - with a frequency of 5.86 and 0.93 %, respectively. Viable and promising embryos follow much stricter time frames of division, and embryos that stop developing, as a rule, go beyond the time range and more often demonstrate division anomalies.