Correlation between the cell number and diameter in bovine embryos produced in vitro.

This study was designed to examine the effects of age and developmental stage of in vitro-produced bovine embryos on the cell number of the embryos and to investigate the correlation between the cell number and diameter in the embryos. The diameter and cell number in blastocysts and expanded blastocysts collected on days 7-9 after in vitro fertilization (IVF) were examined. Although the diameters of the blastocysts collected on days 7 and 8 after IVF were smaller than those of the expanded blastocysts collected on day 9, the cell number in both types of embryos was similar. The cell numbers of the blastocysts and expanded blastocysts decreased with increasing embryo age. There were positive correlations between the cell number and diameter in bovine embryos at each stage collected on each day after IVF. However, the value of the correlation coefficient in the day-9 expanded blastocyst group tended to be higher than that in the other groups. These results indicate that the cell number of in vitro-produced embryos is affected by the embryonic stage and age. The diameter of the embryo may be potentially used for the viability testing of the expanded blastocysts collected on day 9 after IVF.