Transition of Cleavage Divisions during In Vitro Development of Bovine Embryos

抄録

Bovine in vitro fertilized (IVF) embryos were cultured in either CR1aa (CR1) or TCM-199 (TCM) medium and compared for their daily development based on the number of cleavage divisions (CDN), as calculated from the total cell numbers of the embryos. Embryos with advanced developmental stage and higher morphological quality were selected for use in the experiment. The relation between the CDN and the number of embryonic days after IVF in both groups showed a linear correlation; no significant difference (P > 0.05) was found between the two groups. However, CDN on days 3 and 8 after IVF in the CR1 group did not increase, which suggests that transient developmental arrests occurred at these stages. In contrast, embryos in the TCM group showed a transient developmental arrest 3 d after IVF, but CDN increased regularly with age in days at later stages of culture with 100 μM β-mercaptoethanol. A significant difference was found between the regression lines of the two groups during 5-9 d after IVF (P < 0.001). Consequently, numerical analysis of embryonic development in terms of CDN enabled objective evaluation of the developmental progress of bovine IVF embryos.