INFLUENCE OF CULTURE SYSTEM AND OXYGEN-TENSION ON THE DEVELOPMENT OF OVINE ZYGOTES MATURED AND FERTILIZED IN-VITRO

The development and quality of ovine zygotes matured and fertilized in vitro were compared after coculture with oviductal cells (CZB-199 sys tem) and culture in synthetic oviduct fluid medium without cells (SOF system). The effect of two oxygen concentrations (5% and 20%) on the d evelopment of ovine zygotes in SOF medium was also studied. More ovine zygotes reached the blastocyst stage when culture in SOF medium was p erformed in 5% O-2 rather than 20% O-2. A greater number of blastocyst s was obtained after culture in the SOF system than coculture in the C ZB-199 system. Proportions of grade I (excellent), II (good), III (fai r) and IV (poor) blastocysts did not differ significantly between the SOF and CZB-199 systems. Histological examination of hatched blastocys ts revealed a superiority of the SOF system for the following: a great er number of total and trophoblastic cells in grade I and II blastocys ts; more endodermic cells in grade I blastocysts, higher mitotic index in the inner cell mass of grade II blastocysts and in total and troph oblastic cells of grade I, II and III blastocysts;more grade III blast ocysts with mitosis in the inner cell mass; and a lower pyknotic index in the inner cell mass of grade I, II and III blastocysts. Culture in the SOF system improved the rate and quality of blastocysts in compar ison with the CZB-199 system. Furthermore, culture in SOF medium with 5% O-2 provided more blastocysts than culture in the presence of 20% O -2.