Effect of ovariectomy on blastocyst expansion and survival in ferrets (Mustela putorius furo)

The initial objective was to investigate whether progesterone alone can support full blastocyst expansion in ferrets ovariectomized on Day 5 post coitum (p.c.). By Day 11 p.c. blastocysts from control animals had expanded to approximately 2000 microns in diameter, whereas by Days 11 or 14 p.c. blastocysts from ovariectomized animals given progesterone had diameters of < 1000 microns. Thus, ovarian factors in addition to progesterone are apparently required for normal blastocyst expansion in this species. Subsequent experiments indicated that an initial stage of expansion (from approximately 200 microns to approximately 400 microns) occurred regardless of whether ovariectomy was performed on Day 2 or 3 p.c. A second stage of expansion resulted in blastocysts of approximately 700 microns in diameter and it occurred in ovariectomized animals if progesterone was given or if ovariectomy was delayed until Day 5 p.c. A third phase of expansion resulted in blastocysts of approximately 2000 microns in diameter and occurred only if ovariectomy was delayed until Day 8 p.c. Although blastocyst expansion appeared normal in these animals, implantation did not occur in the absence of progesterone replacement. In addition, blastocysts retained in the oviduct by ligation of the uterotubal junction failed to expand beyond approximately 400 microns in diameter. These results suggest that progesterone acts upon the uterus to promote blastocyst expansion up to a diameter of approximately 1000 microns and that additional ovarian factors are required for further blastocyst expansion.