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 P4 treatment 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 30 post-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 9 and 12 ewes, and 0% for asynchronous transfers to day 18 and 30 ewes. On day 39 posttransfer ,pregnancy rates remained 60% for day 6 ewes,33% for day 9 ewes,and 0% for day 12,18, and 30 ewes. The P4 treatment 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.
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 P4 treatment 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 30 post-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 9 and 12 ewes, and 0% for asynchronous transfers to day 18 and 30 ewes. On day 39 posttransfer ,pregnancy rates remained 60% for day 6 ewes,33% for day 9 ewes,and 0% for day 12,18, and 30 ewes. The P4 treatment 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.
