Development of ovine embryos co-cultured on oviductal cells, embryonic fibroblasts, or STO cell monolayers.

One- and two-cell ovine embryos were co-cultured on primary monolayer cultures of ovine oviductal cells (OM) and ovine embryonic fibroblasts (EF) or on monolayers of STO cells (STO), a permanent cell line, to determine whether a co-culture system could be developed for ovine embryos utilizing a well-characterized cell line. More than 65% (n = 64) of embryos co-cultured on OM and STO for 5 days cleaved beyond the "in vitro" block whereas only 26% (n = 35) of embryos co-cultured on EF cleaved to the same degree (p < 0.05). Mitotic inactivation of the monolayer did not alter the response to each cell type. In a second experiment, development of embryos was similar after co-culture on OM or STO cells for both 3 and 6 days. Co-culture of zygotes on OM and STO cells produced 38 and 33% blastocysts after 6 days of co-culture. After embryo transfer, only recipients receiving at least one blastocyst became pregnant. About 33% of the transferred blastocysts produced fetuses. STO cell co-culture may provide the same stimulus to development as OM cell co-culture and may be advantageous for study of the requirements for early ovine embryonic development. In addition, STO cells displayed contact inhibition and formed monolayers that did not overgrow embryos as did primary cultures of ovine oviductal cells.