Development of in-vitro-derived bovine embryos cultured in 5% CO2 in air or in 5% O-2, 5% CO2 and 90% N-2

To evaluate the effects of a three gas mixture of 5% O-2, 5% CO2 and 90% N- 2 (OCN) on preimplantation embryo development, bovine in-vitro fertilizatio n (IVF) oocytes were cultured in a defined medium (mBECM) with various supp lements either under 5% CO2 in air or under OCN, When cultured in mBECM alo ne, embryo development was significantly stimulated in OCN compared to 5% C O2 in air (experiment 1). In the OCN atmosphere, blastocyst formation was f urther increased after addition of fetal bovine serum (FBS; 10%) or FBS + c umulus granulosa cells (CGC) to mBECM. The ratio of blastocysts to 8-cell e mbryos, number of hatched blastocysts and embryo diameter were markedly inc reased, and zona thickness was decreased after FBS addition. However, devel opment up to the morula stage was fully supported by mBECM alone. There was no significant effect of beta-mercaptoethanol (ME; 10 mu M) in OCN. In the 5% CO2 atmosphere, embryo development was significantly (P < 0.05) enhance d after addition of FBS + CGC + ME. In experiment 2, in OCN, FBS added at 6 0 h post-insemination was effective in stimulating blastocyst formation, bu t changes in medium volume per oocyte from 13.6 to 1.36 mu l had only a mar ginal effect. In conclusion, OCN gas mixture provides a suitable atmosphere for early embryo growth in vitro and mBECM + FBS is the optimal culture me dium under this atmosphere.