Studies on Marsupial Reproduction. 2. The oestrous cycle of Setonix Brachyurus.

Abstract

Setonix brachyurus Quoy and Gaimard is polyoestrous, the length of the cycle being about 28 days. In the wild and in the newly domesticated female, oestrous cycles are resumed in late January after an anoestrous period of 3-5 months. During this period oestrus does not occur and ovary and uterus are shrunken and quiescent. Domestication for periods exceeding 1 yr results in a greatly shortened anoestrous period, culminating in a condition in which oestrus is repeated at regular monthly intervals throughout the year. Pro-oestrus is accompanied by rapid growth of one Graafian follicle, mitotic activity in the uterus, and usually by the onset of cornification in the vaginae and appearance of partly cornified cells in the smear. At oestrus the largest follicle reaches a diameter of almost 3.0 mm. Behavioural oestrus lasts about 12 hr. Ovulation follows 12-24 hr after oestrus and is independent of the act of copulation. Invasion of the collapsed follicle by blood vessels and the growth of a corpus luteum takes place after ovulation. Under the influence of the corpus luteum a luteal phase occurs in the uterus and lasts until about 18 days after oestrus. During the period of activity of the corpus luteum the vaginal smear is almost entirely composed of non-cornified cells and leucocytes. Following the cessation of the luteal phase degenerative changes occur in the uterus and the uterine glands are invaded by leucocytes. The changes during the oestrous cycle in Setonix are compared with those occurring in Didelphis and in other marsupials.