Analysis of Vaginal Cytology to Monitor the Estrous Cycle

The vaginal epithelium of many mammalian species is responsive to changes in circulating estrogen levels. The value of vaginal cytology in monitoring the estrous cycle of rodents is widely recognized. In all species, increasing proportions of mature cells are correlated with the pre-estrus rise in estrogen and with estrous behavior. Despite the logistical difficulty of obtaining vaginal cells from nondomestic species, the estrous cycles of a few large carnivores have been studied, including three species of bears. However, data reported in these studies represented a single or very few vaginal swabs for each bear, which yielded little information about changes in cytology throughout the estrous cycle.

Sequential collection of vaginal cells from individual bears has been described only in the giant panda (by the Reproductive Physiology Division of CRES). Facilitated by behavior modification of captive specimens, swabs are easily and non-invasively obtained, allowing frequent collection without animal stress. The rapidity with which vaginal cytology can be analyzed, and the close correlation of vaginal cell morphology and estrogen levels, make the technique useful in captive exotic animals for timing artificial insemination or introductions for natural mating.

In addition to the giant panda, vaginal cytology analysis has proven to be a useful adjunct to behavioral and endocrinological parameters for captive dolphins, margays, clouded leopards, sun bears, and tayras. The goal of this project is to utilize vaginal cytology for routine estrous cycle monitoring of bears and to develop the technique for other mammalian species.