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Evidence of Folliculogenesis and the Potential of Oocyte Recovery from Koalas with Different Levels of Reproductive Pathology
by
, , , , and
Stephen D. Johnston
1,2,*
,
Jackson Boyd
1,2,
Patricio D. Palacios
3,
Julien Grosmaire
4,
Alexander Lee
1,2,
Lyndal Hulse
1,2,
Leslie Vega
5,
Michael Pyne
5,
Andres Gambini
2,3
and
Chiara Palmieri
2
1
School of Environment, The University of Queensland, Gatton 4343, Australia
2
School of Veterinary Science, The University of Queensland, Gatton 4343, Australia
3
School of Agriculture and Food Sustainability, The University of Queensland, Gatton 4343, Australia
4
Endeavour Veterinary Ecology, Donnybrook 4510, Australia
5
Currumbin Wildlife Sanctuary, Currumbin 4223, Australia
*
Author to whom correspondence should be addressed.
Biology 2025, 14(10), 1435; https://doi.org/10.3390/biology14101435
Submission received: 18 September 2025
/
Revised: 15 October 2025
/
Accepted: 15 October 2025
/
Published: 17 October 2025
(This article belongs to the Special Issue Feature Papers on Developmental and Reproductive Biology)
Simple Summary
Koalas in eastern Australia are under an increasing threat of extinction from reproductive disease (chlamydiosis) and habitat degradation. We present data on the evidence of ovarian activity and the potential of oocyte collection from ovaries of koala cadavers with varying degrees of reproductive pathology. While we have demonstrated that the majority of koala ovaries show evidence of active folliculogenesis despite varying degrees of reproductive pathology and that oocyte collection from the ovaries of post-mortem koalas is possible, further studies that facilitate in vitro maturation of oocytes leading to transfer of fertilized embryos are now required. This work represents a cautious positive step forward towards the establishment of frozen genome bank for the koala.
Abstract
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 Chlamydia 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.
