Additional effect of epidermal growth factor during in vitro maturation for individual bovine oocytes using a chemically defined medium

This study was performed to establish an individual bovine oocyte-IVP system using a chemically defined simple medium (mSOFaa containing I mg/ml polyvinyl alcohol: PVA) and to investigate the effects of epidermal growth factor (EGF) during oocyte maturation on in vitro maturation, fertilization and embryonic development. Cumulus-oocyte complexes were collected from bovine ovaries and were matured in mSOFaa containing PVA (control medium) supplemented with 0, 1, 10 or 50 ng/ml of EGF. Two further groups (TCM199 and mSOFaa, supplemented with 10% fetal calf serum were also included. In this study, mSOFaa containing PVA were used as a basic medium for fertilization and embryo development in vitro. Experiments were conducted in both group- and individual-IVP systems. In the group-IVP system, the proportion of matured oocytes (MII) in the control medium (62.7% 5.0%) was significantly (p < 0.05) lower than in all other treatments, and in the individual-IVP system, the addition of I ng/ml EGF significantly (p < 0.05) increased the maturation rate (I ng/ml EGF vs control: 76.2% +/- 5.4% vs 57.1% +/- 14.4%). The addition of EGF did not affect the proportions of penetrated and normally fertilized oocytes in either individual- or group-culture systems. In the group-IVP system, no significant difference among treatments was found in the rate of blastocyst formation, whereas in the individual-IVP system the control medium supplemented with 10 ng/ml EGF resulted in a significantly (p < 0.05) higher the rate of blastocyst formation (20.0 +/- 15.2%) than that in the control medium (6.2% +/- 3.5%). These results indicate that bovine oocytes can successfully develop to blastocysts in an individual-IVP system using a single chemically defined medium, and that the group-IVP system also resulted in a similar level of blastocyst formation to that in a standard multiple-media system in our laboratory. The effect of EGF during oocyte maturation medium differed depending on whether embryos were cultured individually or in groups.