Influence of in vitro oxygen concentrations on preimplantation embryo development, gene expression and production of hanwoo calves following embryo transfer

This study evaluated the effects of two different oxygen (O-2) concentrations on in vitro embryo development, embryo quality, and gene expression and the in vivo development following embryos transfer to recipients of natural and synchronized estrus in bovines. Cumulus oocyte complexes were in vitro matured in TCM199 supplemented with FSH (10 mu g/ml), LH (10 mu g/ml), and 10% (v/v) FBS. Presumptive zygotes were cultured in SOF medium either under 5% (low) or 20% (high) O-2 in air. Cleavage rates did not differ between groups. Blastocyst and hatched blastocyst development in 5% O-2 were significantly (P < 0.05) higher than in 20% O-2. Total cell number of in vivo blastocyst was significantly (P < 0.05) higher than that of in vitro blastocyst. ICM ratio and apoptosis of in vivo blastocyst were significantly (P < 0.05) lower than that of in vitro blastocyst. Using real time PCR, we have found that for the set of genes (GLUT-1, MnSOD, VEGF, Bax, and Bcl-2) analyzed, there were differences in mRNA expression between in vitro produced (IVP) and in vivo produced embryos. Interestingly, the abundance of transcript for IFN-tau in IVP embryos produced under 5% O-2 concentration was similar to in vivo counterparts. The pregnancy and twin rates of natural recipients were significantly (P < 0.05) higher than those of synchronized counterparts, No significant difference in the offspring sex was observed. In conclusion, low (5%) O-2 concentration during IVC was beneficial for enhancing the embryo quality and recipients of natural estrus were more suitable than synchronized estrus for stable production of Hanwoo calves.