Reproductive lesions identified in European captive great apes

This multi-institutional study investigated ante- and post-mortem reproductive lesions in captive great apes within European zoos in the great ape Taxon Advisory Group (TAG) European Association of Zoos and Aquaria (EAZA) ex-situ programs (EEP). These include bonobos (Pan paniscus) (n = 13), chimpanzees (Pan troglodytes) (n = 94), gorillas (Gorilla beringei, Gorilla gorilla) (n = 132) and orangutans (Pongo abelii, Pongo pygmaeus, Pongo tapanuliensis) (n = 67) across 141 collections. Data was collected from 306 post-mortem reports spanning 30 years (1990–2021) from 55 institutions and reproductive health surveys from 65 institutions, representing 45.7% of the current EAZA great ape population. Post-mortem descriptions varied widely, with 46.4% of post-mortem reports not commenting on the reproductive system. Among those that did include it, 41.5% reported lesions, yet histopathology was performed in only 52.4% of cases, highlighting the need for standardized necropsy protocols that include the routine assessment of the reproductive system and histopathology. Similar frequency and types of reproductive lesions were identified across species, with cystic ovaries and uterine leiomyomas being the most frequent findings in females, and testicular degeneration and atrophy in males. Gender was a risk factor in orangutans. Individuals with reproductive lesions were significantly older than those without. Survey data revealed that 2.5% of living great apes had reproductive abnormalities diagnosed, the most common being infertility of unknown cause in 33.3% of reported cases. The significant discrepancy in frequency and types of reproductive lesions diagnosed between the ante- and post-mortem exams suggests underdiagnosis of asymptomatic and subclinical conditions within the current EAZA great ape population. Reproductive lesions may compromise individual welfare and reduce breeding success, with implications for the genetic management of endangered species. A literature review of 52 articles identified uterine leiomyoma as the predominant reported lesion (86.1%), mostly in chimpanzees, contrasting with cystic ovaries which was the most frequent finding in this study. These findings underscore the importance of routine reproductive system monitoring in geriatric and breeding-age individuals and the need for standardized diagnostic protocols.