Vaginal cytology and vulvar swelling as indicators of impending estrus and ovulation in the giant panda (Ailuropoda melanoleuca)

Abstract

The giant panda is critically endangered in its native habitat, which is continually depreciated by the pressure of human population growth, and the small captive population is not yet self-sustaining. Female giant pandas are seasonally monoestrous with spontaneous ovulation. Precise monitoring of the estrous cycle to pinpoint the time of ovulation is critical for the success of both timed mating and artificial insemination. Vaginal cytology is a useful adjunct to endocrinological data in describing the estrous cycle in many species, including domestic carnivores; however, it has not been used effectively in the giant panda. In this study, vaginal swabs were obtained from four nulliparous females ranging in age from 6 to 14 years. Cells were stained with Papanicolaou stain and classified as basophils, intermediate cells, or superficial cells based on traditional criteria. In addition, cell color changes from the basophilic through the acidophilic and keratinized stages were recorded. The size and color of the vulva of a single female was scored daily on a scale of 0-3, with anestrus characterized as 0. The day of ovulation was retrospectively designated as day 0 based on urinary estrogen concentrations, behavior, and morphological indicators. The vulva began to swell between days -11 and -9, with peak tumescence on the day of ovulation. The percentage of superficial cells began to increase by day -8 to -7, and peaked between days -2 and +2. A chromic shift occurred on day -8, when the majority of vaginal cells changed from basophilic to acidophilic without any accompanying nuclear or cytoplasmic changes. A second chromic shift was observed on day -2, when keratinized cells replaced acidophilic cells as the majority of vaginal cells. By day +4, all parameters had returned to baseline except vulvar swelling, which slowly subsided over the next several days. These data show the correlation of trichrome-stained vaginal cytology with other measured indicators of estrus in the giant panda, and its predictive value in determining the time of ovulation.

Serial Transrectal Ultrasonography for Monitoring the Reproductive Activity of the Asiatic Black Bear (Ursus thibetanus ussuricus)

“…In addition, this technique has also been investigated for application in improving the reproductive efficiency of bears (Durrant et al. ; Frederick et al. ).…”

Dynamics of Male–Female Multimodal Signaling Behavior across the Estrous Cycle in Giant Pandas (Ailuropoda melanoleuca)

“…In cases where no mating occurred (N = 4), we used the peak in vulvar swelling (Durrant et al. ). (2) Because the duration of behavioral estrus is variable (R. R. Swaisgood, unpubl.…”

“…the day of, and the day after successful mating. In cases where no mating occurred (N = 4), we used the peak in vulvar swelling (Durrant et al 2003). (2) Because the duration of behavioral estrus is variable (R. R. Swaisgood, unpubl. data), we chose to define 'estrus' by the presence of the following, not explicitly social, behavioral, and physical indices: elevated scent-marking, water play, backwards walking, rolling, masturbation, and vulvar swelling and reddening.…”

“…Female giant pandas have a single, annual estrus, with mating receptivity lasting only 1-3 d (Schaller et al 1985). Females undergo a 10-to 14-d period of follicular development prior to ovulation, which appears to be spontaneous (Durrant et al 2003). During follicular development, estrogen levels begin to climb, undergo a rapid elevation and subsequent precipitous drop during the 2-to 3-d peri-ovulatory period (Kersey et al 2010).…”

American black bear mating behavior and chemosensation of estrus

“…Vulva score is strongly correlated with estrogen levels and is a physiological indicator of the estrous cycle in a variety of carnivores, including dogs (Nishiyama et al 2000), giant pandas (Ailuropoda melanoleuca; Durrant et al 2003), and sun bears (Helarctos malayanus; Frederick et al 2010). We adapted the vulva scoring system described in Durrant et al (2003) for use with black bears under field conditions. Three observers independently determined daily vulva scores for each female.…”