Presence of males affects the incidence of ovulation after pouch young removal in brushtail possums (Trichosurus vulpecula).

Abstract

The traditional method for inducing and synchronising oestrus in the brushtail possum (Trichosurus vulpecula) is by removal of their suckling pouch young (RPY). However, our studies have recently shown that, in addition to wide variation between animals in the time of ovulation after RPY, a proportion of animals failed to ovulate. Evidence from several mammalian species indicates that the presence of males can stimulate ovarian activity and synchronise oestrus in females. The aim of this study was to determine the effect of the male on the oestrous cycle of the female brushtail possum after RPY. A total of 67 adult female brushtail possums were treated as three replicates. In order to observe the day of preovulatory follicle emergence and ovulation, animals underwent laparoscopic examination at 1-4 day intervals over a period from 0-21 days after RPY. The first replicate (N = 18, May/June 1995) involved only animals kept in isolation from males, whereas the two remaining replicates compared ovarian responses between animals kept with ( N = 10, July 1995; N = 14, June 1996) or in isolation from ( N = 10, July 1995; N = 15, June 1996) males. The incidence of ovulation after RPY was significantly higher in females that were housed with males than in those kept in isolation from males (100%, 92.8% vs. 50.0%, 66.7%, 14.3%; P < 0.001). Every animal that ovulated, had previously had a preovulatory follicle present at the site where the corpus luteum formed. Conversely, none of the animals that failed to ovulate, developed a preovulatory follicle during the period of the study. The range of mean day of preovulatory follicle emergence (6.00-6.86 days), of ovulation (11.80-12.20 days) and the synchrony of ovulation between animals (range 8-17 days) after RPY, were not significantly affected by the presence of males. This study demonstrates for the first time, that the presence of males significantly increases the incidence of ovulation after RPY in the brushtail possum. However neither the timing of reproductive events nor the synchrony of ovulation were affected by presence of the male.