The requirement of progesterone and estrogen for implantation and embryonic development was examined in ferrets ovariectomized on days 7, 8, 10, or 13 of pregnancy (day 0 being the day of mating). Implantation occurred at the normal time, on day 13, in a few but was delayed for several days in the majority of ferrets ovariectomized on day 7 and treated with progesterone alone or combined with estrogen. Similar treatment of ferrets ovariectomized on days 8 or 10 induced implantation on day 13 in all the animals. In all these cases the embryonic development to day 26 was more retarded than that of ferrets ovariectomized on day 13 and injected with hormone(s). Addition of estradiol to the progesterone treatment did not in any case hasten the implantation or improve the embryonic development. It appears that, in many respects, the ferret, like the hamster and the rabbit, requires only progesterone for implantation and subsequent embryonic development. However, the day of ovariectomy in ferrets is of importance in determining whether implantation can be induced at the normal time and whether embryonic development can be maintained by hormonal treatments.
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M. C. Chang (1973) studied this question.