Evidence of Folliculogenesis and the Potential of Oocyte Recovery from Koalas with Different Levels of Reproductive Pathology

Each year, hundreds of female koalas are presented to koala hospitals suffering from a range of morbidities, many of which require euthanasia for animal welfare reasons. These koalas represent a possible resource for genetic recovery by means of oocyte retrieval for genome banking or use in assisted reproductive technology. To examine the feasibility of koala oocyte recovery, this study conducted a preliminary survey of follicular activity and disease presence in fixed ovarian tissues from koala cadavers in South East Queensland. Ovarian activity and pathology were assessed by gross examination and histology. Bursal pathology was categorized into koalas with no, small (<10 mm diameter), moderate (10-20 mm diameter), or large (>20 mm diameter) sized bursae, whereas uterine pathology was diagnosed by an experienced reproductive pathologist. Antral follicles were observed in 94.4% of ovaries recovered from koalas with no bursal or uterine pathology (n = 18/44), 95.2% of the ovaries of koalas with bursal but no uterine pathology (n = 11/44), 100% of the ovaries of koalas showing only uterine pathology (n = 4/4) and 89.5% of ovaries from koalas with both bursal and uterine pathology (n = 11/44). Of the fixed ovarian tissue suitable for PCR <i>Chlamydia</i> detection (35/44), none were positive. As proof of concept, oocytes were also collected and evaluated from six koala cadavers within 2 h post-mortem. Although further studies are required to determine the quality and viability of the retrieved koala oocytes, our preliminary survey provides strong evidence that ovarian activity mostly continues unabated, irrespective of reproductive pathology, and that oocytes can be recovered successfully.