Effects of oxygen concentration and oviductal epithelial tissue on the development of in vitro matured and fertilized bovine oocytes cultured in protein-free medium.

Examination was made of the effects of oxygen concentration and supplementation of bovine oviductal epithelial tissue (BOET) on the development of bovine in vitro matured and fertilized (IVM/IVF) oocytes in a protein-free medium. The IVM/IVF embryos were cultured in protein-free tissue culture medium 199 supplemented with or without BOET under 5% CO2 in air (20% O2) or 5% CO2, 5% O2 and 90% N2 (5% O2). We found that blastocyst development without BOET at 5% O2 was the same as that with BOET at 20% O2 (30 vs 33%); BOET suppressed blastocyst development at 5% O2 (4%). Blastocysts cultured without BOET at 5% O2 developed into normal fetuses after transfer to recipient heifers. Examination was also made of oxygen pressure in the medium cultured with or without BOET at 20% O2 or 5% O2 by a blood gas analyzer. Oxygen pressure in the medium cultured with BOET at 20% O2 was lower than that without BOET (111.0+/-13.3 vs 149.2+/-1.3 mmHg). These results indicate that bovine IVM/IVF embryos can develop to the blastocyst stage in a protein-free medium without somatic cell support at low oxygen concentration (5%) and that the beneficial role of BOET for embryonic development may be to reduce oxygen concentration in the medium.