Œstrus and pseudo-pregnancy in the ferret

Abstract

The ferret has been but little used for experimental laboratory work on reproduction, although its small size and marked sexual changes, together with the fact that it ovulates only after coitus, make it a very suitable species for laboratory investigations. The study of the ferret's œstrous cycle, however, formed the subject of an investigation by one of us some 25 years ago (Marshall, 1904), when it was shown that there was normally a well-marked breeding season, extending from about March to August, and an anœstrum during the rest of they year. The fact was verified that œstrus in the absence of the male may extend over a very prolonged period (as much as 6 weeks) and that it is characterised by a very well marked swelling of the vulva. Congestion of the uterus and other internal changes were also described. Futhermore, it was ascertained that ovulation in the ferret, as in the rabbit, does not occur spontaneously, but depends upon sexual intercourse, a fact which was confirmed later by Robinson (1918). It has been shown by a number of authors (Ancels and Bouin, 1910; Schil, 1912; Hammond and Marshall, 1914) that in the rabbit the condition known as pseudo-pregnancy can be induced by a sterile mating (e. g., the doe copulating with a vasectomised buck), the stimulus of sexual intercourse resulting in ovulation and the subsequent formation of corpora lutea, which develop as in true pregnancy up to about the 16th day, and during this time bring about a growth of the uterine musosa and an hypertrophy of the mammary glands comparable to that which occur during true pregnancy. In the present investigation experiments were carried out to determine whether pseudo-pregnancy could be induced similarly in the ferret, and a series of observations was made upon the correlated changes in the ovaries, uterus, mammary glands, and vulva in various stages and conditions during the seasons of reproductive activity.