In ferrets uterine swellings appeared on Day 11 of pregnancy (Day 0 = mating) and implantation occurred on Day 12. In animals ovariectomized on Day 6 and receiving no hormonal treatment, implantation did not take place and the blastocysts were either collapsed or degenerated by Day 17 and had almost completely disappeared by Day 21. Treatments with progesterone or progesterone and estrogen were beneficial to the survival of blastocysts; however, incipient implantation, as indicated by the Niagara Sky Blue reaction and uterine swelling, was consistently delayed for 1 week or longer beyond the normal time. Furthermore, no embryos were present in the uterine swellings on Days 23-28, suggesting that the blastocysts degenerated soon after implantation had been initiated. The failure of several regimens of progesterone and estrogen to induce normal implantation and development of embryos in the ovariectomized ferret suggests that hormonal control of implantation is very delicate and exact in this species.
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M. C. Chang (1972) studied this question.