Effect of .BETA.-Merchaptoethanol on the Preimplantation Development of Bovine Embryos Fertilized In Vitro.

The present study investigated effects of β-merchaptoethanol (β-ME) on the development of bovine embryos derived from In vitro matured and fertilized (IVM-IVF) oocytes. IVM oocytes were inseminated with frozen-thawed bovine sperm, and at 24, 48 and 72 h after insemination, 2-, 8-and 16-cell embryos, respectively, were transferred to TCM-199 medium containing 5% fetal bovine serum and 0, 5, 10, 20, 50 or 100 μm β-ME without a cumulus cell monolayer or with a cumulus cell monolayer but without addition of β-ME as a control. All embryos were subsequently incubated such that the total duration of culture was 8 days. The addition of low concentrations ( 5 or 10μM) of β-ME significantly enhanced the development of all the embryos to the blastocyst stage. High concentrations (20, 50 or 100μM) of β-ME were effective only for the development of 8-and 16-cell embryos, but not of 2-cell embryos, to the blastocyst stage. Compared with embryos in the co-culture system (control), 2-cell embryos that were cultured with β-ME but without a cumulus cell monolayer showed significantly lower rates of development to the blastocyst stage. However, even though without a cumulus cell monolayer, 8-cell embryos showed the same rates of develop-ment to the blastocyst stage as controls when low concentrations of β-ME (5 or 10μM) were added to the medium. Furthermore, significantly higher rates of development of embryos to the blasto-cyst stage were obtained when 16-cell embryos were cultured in medium supplemented with 20μM β-ME than that of controls. Twenty blastocysts developed from 16 cell IVM-IVF embryos in the medium containing 20μM β-ME were transferred to 20 recipients, and 11 of them became pregnant, resulting in 10 calves. These results indicate that β-ME is effective for blastocyst development of embryos that are cultured without a cumulus cell monolayer, and the effect is remarkable for embryos of advanced stages.