摘要Synchronization of development between the embryo and uterus is required for successful pregnancy establishment.Transfer of early embryos requires synchrony with the recipient uterus of 2 days or less in sheep.because asynchrony of 3 days or more results in failure of pregnancy recognition signaling for maintenance of corpus luteum(CL)and progesterone(P4)production and/or uterine support of the embryo.The objective was to determine if P4treatment of recipient ewes would obviate the need for pregnancy recognition signaling and maintain a uterine environment conducive to embryo survival after asynchronous transfer,thereby establishing a universal recipient.Embryos(morulae/blastocysts)were recovered on day 6 from super-ovulated donor ewes.Recipient ewes received 25 mg P4 daily from day 6 post-estrus until 60 days after embryo transfer.Embryos were transferred into recipients on day 6,9,12,18,or 30post-estrus.The pregnancy rate on day 22 post-transfer was 60% for synchronous transfers to day 6 ewes.44% and 22% for asynchronous transfers to day 9and 12 ewes.and 0% for asynchronous transfers to day 18 and 30 ewes.On day 39 post-transfer,pregnancy rates remained 60% for day 6 ewes.33% for day 9ewes,and 0%　for day 12,18.and 30 ewes.The P4treatment did extend the Window of uterine receptivity to early embryos in ewes by one day.but did not create a universal recipient.Available results support the idea that a window of uterine receptivity to the conceptus exists in sheep that is independent of pregnancy recognition signaling.