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% O-2) or 5% CO2, 5% O-2 and 90% N-2 (5% O-2). We found that blastocyst development without BOET at 5% O-2 was the same as that with BOET at 20% O-2 (30 vs 33%); BOET suppressed blastocyst development at 5% O-2 (4%). Blastocysts cultured without BOET at 5% O-2 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% O-2 or 5% O-2 by a blood gas analyzer. Oxygen pressure in the medium cultured with BOET at 20% O-2 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.