EFFECT OF OVIDUCT EPITHELIAL-CELLS ON THE FERTILIZATION AND DEVELOPMENT OF SHEEP OOCYTES IN-VITRO

The study examined whether co-culture with oviductal epithelial cells was ofbenefit to ovine in vitro fertilization (IVF) and embryo culture procedures utilizing a well characterized culture system based on a s ynthetic oviductal fluid medium (SOFM) supplemented with serum in a 90 % N-2, 5% O-2, 5% CO2, atmosphere at 38.6 degrees C. Two experiments w ere carried out. In Experiment 1, comparison was made between the freq uency of fertilization and development of in vitro matured (IVM) oocyt es cultured in the absence (Group 1) or presence of oviductal cells fo r a 24 h (Group 2), 48 h (Group 3) or 96 h (Group 4) period post insem ination. In Experiment 2, comparison was made between the development of IVM oocytes fertilized and cultured in vitro for 7.5 days in the ab sence or presence of oviductal cells with IVM oocytes which had been f ertilized in vitro for 20 h in the presence of oviductal cells and the n transferred to the oviducts of a recipient ewe, 30 h post oestrus, f or a 6.5 day period of in vivo culture. Similar rates of fertilization (54-58%) and blastocyst development from cleaving zygotes (48-69%) we re achieved in both experiments in vitro with no evident benefit of in cluding oviductal cells. In fact, fewer (P=0.02) blastocysts developed from cleaved embryos when co-cultured for the 96 h period (Group 4). Whilst the blastocyst development rates obtained in vitro (45-58%) wer e similar to, or higher than (P=0.03), those obtained in vivo (43%), m ore than 50% of in vitro cultured embryos in both experiments showed e vidence of fragmentation and/or irregular cleavage as well as a lack o f firm compaction at the morula stage. Also the blastocysts that had n ot hatched, or hatched by 7.5 days of in vitro culture had significant ly fewer cells than those cultured in vivo (P<0.003). The results conf irm that SOFM supplemented with serum can support the fertilization an d development of ovine oocytes to the blastocyst stage in vitro, but t hat development is compromised compared with that obtained in vivo and that these defects were not offset by including oviductal cells in th e culture media. However, it should be noted that the composition of t he medium and gaseous atmosphere developed for the IVF embryo culture procedures are recognized as being suboptimal to the maintenance of th e viability of somatic cells, highlighting the difficulties of selecti ng culture conditions suited for both embryonic and somatic cells deve lopment, a primary requisite for realizing the potential beneficial ef fects of co-culture on embryo viability.