PRESENCE OF MALES AFFECTS THE INCIDENCE OF OVULATION AFTER POUCH YOUNG REMOVAL IN BRUSHTAIL POSSUMS (TRICHOSURUS-VULPECULA)

The traditional method for inducing and synchronising oestrus in the b rushtail possum (Trichosurus vulpecula) is by removal of their sucklin g pouch young (RPY). However, our studies have recently shown that, in addition to wide variation between animals in the time of ovulation a fter RPY, a proportion of animals failed to ovulate, Evidence from sev eral mammalian species indicates that the presence of males can stimul ate ovarian activity and synchronise oestrus in females. The aim of th is 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 observ e the day of preovulatory follicle emergence and ovulation, animals un derwent laparoscopic examination at 1-4 day intervals over a period fr om 0-21 days after RPY. The first replicate(N= 18, May/June 1995) invo lved only animals kept in isolation from males, whereas the two remain ing replicates compared ovarian responses between animals kept with (N = 10, July 1995; N=14, June 1996) or in isolation from (N= 10, July 19 95; N=15, June 1996) males. The incidence of ovulation after RPY was s ignificantly higher in females that were housed with males than in tho se kept in isolation from mares (100%, 92.8% vs. 50.0%, 66.7%, 14.3%; P < 0.001). Every animal that ovulated, had previously had a preovulat ory follicle present at the site where the corpus luteum formed. Conve rsely, none of the animals that failed to ovulate, developed a preovul atory follicle during the period of study. The range of mean day of pr eovulatory follicle emergence (6.00-6.86 days), of ovulation (11.80- 1 2.20 days) and the synchrony of ovulation between animals (range 8-17 days) after RPY, were not significantly affected by the presence of ma les. 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 event s nor the synchrony of ovulation were affected by presence of the male . (C) 1998 Elsevier Science B.V.