OOCYTE RECOVERY AND MATURATION IN THE AMERICAN BLACK BEAR (URSUS-AMERICANUS) - A MODEL FOR ENDANGERED URSIDS

A study was conducted to determine if meiotic maturation could be indu ced in ovarian oocytes of the American black bear (Ursus americanus), a model for gamete ''rescue'' techniques for endangered ursids. Ovarie s obtained from 48 black bears yielded 2,403 oocytes (51.1 +/- 4.9/fem ale), of which 777 (32.3%) were morphologically classified as excellen t quality. More total oocytes were recovered from donors that were ane strous compared to luteal/pregnant (P < 0.05) at the time of ovarian e xcision. Delaying the recovery of oocytes from antral follicles within excised ovaries from 12-24 hr to 25-36 hr had no effect (P > 0.05) on the overall number of high quality oocytes recovered or subsequent ma turational ability. The highest incidence of metaphase Il was reached between 48 and 60 hr of in vitro incubation. Donor status (anestrous v s. luteal/pregnant) had no influence on the oocyte maturation rate by 24 or 48 hr, but by 60 hr, more (P < 0.05) oocytes recovered from anes trous females (43.9%) had achieved metaphase II compared to luteal/pre gnant counterparts (23.1%). In preliminary trials involving endangered ursids, 54 ovarian oocytes were recovered from three aged sun bears ( Helarctos malayanus), of which 72.2% were excellent quality and 15.4% matured in vitro to metaphase II. Similarly, 119 antral oocytes were r ecovered from two aged sloth bears (Melursus ursinus), of which 41.2% were excellent and 17.5% matured in vitro. These results demonstrate t hat: (1) ursid oocytes undergo nuclear maturation in vitro; (2) reprod uctive status of the donor influences the total number and maturationa l ability of recovered oocytes; and (3) preliminary observations sugge st the American black bear to be a useful model for developing oocyte rescue techniques for related but endangered species. (C) 1994 Wiley-L iss, Inc.