Embryonic stimulation of ovine and bovine corpora lutea

Preimplantation embryos, recovered from sheep on Days 13-15 of pregnancy, were incubated with luteal tissue from cyclic ewes. Extracts of ovine embryos were incubated with luteal tissue from cyclic Holstein cows. Embryos and embryo extracts significantly increased progesterone production by ovine and bovine luteal tissue in vitro. The embryos themselves did not produce measurable amounts of progesterone. We suggest that the ovine preimplantation embryo produces a substance with luteotrophic properties which contributes to the maintenance of early pregnancy.