Transport and development of embryos transferred to the oviducts and uteri of entire and ovariectomized ewes

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Abstract
Embryos collected from donor ewes 2 or 3 days after estrus were transferred synchronously to the oviducts or uterine horns of entire or ovariectomized ewes and 2-4 days after transfer the embryos were recovered by flushing the uteri and oviducts. Ovariectomized ewes were treated with all, or part, of a steroid hormone regimen designed to simulate ovarian secretion, in entire ewes of progesterone during the luteal phase before estrus, of estradiol around estrus and of progesterone during the luteal phase after estrus. Irrespective of treatment regimen in ovariectomized ewes, only .ltoreq. 50% of embryos transferred to the oviducts were recovered and the majority remained in the oviducts. Most of those remaining in the oviducts showed apparently normal development. In ewes on the complete regimen all of 3 embryos recovered from the uterus had developed normally, whereas none of 7 recovered from the uteri of ewes treated with only part of the regimen had developed normally. Most embryos transferred to the oviducts of entire ewes reached the uterus within 3 days of transfer and, irrespective of whether located in the uterus or oviducts, almost all had developed normally. Few 2-day embryos survived transfer to the uterus. When transfer was delayed to day 3, 70-80% of embryos recovered from entire ewes, and ovariectomized ewes given the full regimen, had developed normally, whereas only 20-30% of embryos recovered from ovariectomized ewes given part of the regimen developed normally. Delayed transport of embryos from the oviducts to the uteri of ovariectomized ewes seemed to be due to deficiencies of the treatment regimen or residual effects of ovariectomy. The steroid hormone requirements for continued development in the oviducts were not critical, whereas requirements both of steroid hormone regimen and of time of transfer were critical for continued development in the uterus.