PREIMPLANTATION DEVELOPMENT OF IN-VITRO-MATURED AND IN-VITRO-FERTILIZED OVINE ZYGOTES - COMPARISON BETWEEN COCULTURE ON OVIDUCT EPITHELIAL-CELL MONOLAYERS AND CULTURE UNDER LOW-OXYGEN ATMOSPHERE

The roles of medium composition, serum source, embryo coculture, and c ulture under low O2 conditions on the development of in vitro-matured and in vitro-fertilized (IVMF) ovine zygotes were investigated in thre e separate experiments. In the first experiment, the proportion of coc ultured IVMF zygotes developing to the blastocyst stage was significan tly higher (38.0% vs. 3.5%; p < 0.05) than that of non-cocultured zygo tes treated within three embryo culture media (TCM-199 + 10% fetal bov ine serum [FBS]; bicarbonate-buffered, glucose-free synthetic oviduct fluid medium [mod-SOFM] + 10% FBS; and bicarbonate-buffered BSA-free T yrode's salt solution [mod-TALP] + 10% FBS) under a 5% CO, atmosphere in air. In a second experiment, a significantly higher (p < 0.05) prop ortion of cocultured zygotes placed in TCM-199 medium survived to the blastocyst stage (37.4% blastocysts vs. 23.4% in mod-SOFM). No signifi cant effect of serum (FBS vs. human serum [HS]) was observed on embryo nic development, but coculture was confirmed to exert a significant in fluence on development to the blastocyst stage. In the final experimen t, survival of the embryo under a reduced oxygen (5% CO2:5% O2:90% N2) atmosphere was investigated. In contrast to results in the initial ex periments, embryonic survival was significantly higher (p < 0.05) in t he non-cocultured treatment groups (21.9% blastocysts vs. 0.4% for coc ultured zygotes). Serum source also had a significant (p < 0.05) influ ence upon the development of non-cocultured zygotes: 32.3% of zygotes cultured with HS progressed to the blastocyst stage vs. 11.5% of zygot es cultured in FBS-supplemented medium. These results have characteriz ed two distinct culture environments, each capable of supporting the d evelopment of high frequencies of unselected IVMF zygotes to the blast ocyst stage in vitro.