Reproductive tract tumours: the scourge of woman reproduction ails Indian rhinoceroses

Abstract

In Indian rhinoceros, extensive leiomyoma, a benign smooth muscle tumour, was sporadically diagnosed post mortem and commonly thought of as contributing factor for reduced fecundity of this species in captivity. However, to date, the prevalence of reproductive tract tumours and their relevance for fecundity are unknown. Our analysis of the international studbook now reveals that females cease reproducing at the age of 18.1±1.2 years; equivalent to a reproductive lifespan of just 9.5±1.3 years. This short reproductive life is in sharp contrast to their longevity in captivity of over 40 years. Here we show, after examining 42% of the captive female population, that age-related genital tract tumours are highly prevalent in this endangered species. Growth and development of these tumours was found to be age-related, starting from the age of 10 years. All females older than 12 years had developed genital tumours, just 7-9 years past maturity. Tumour sizes ranged from 1.5-10 cm. With age, tumours became more numerous, sometimes merging into one large diffuse tumour mass. These tumours, primarily vaginal and cervical, presumably cause widespread young-age infertility by the age of 18 years. In few cases, tumour necrosis suggested possible malignancy of tumours. Possible consequences of such genital tract tumour infestation are hindered intromission, pain during mating, hampered sperm passage, risk of ascending infection during pregnancy, dystocia, or chronic vaginal bleeding. In humans, leiomyoma affect up to 80% of pre-menopause women. While a leading cause for infertility, pregnancy is known to reduce the risk of tumour development. However, different from human, surgical intervention is not a viable treatment option in rhinoceroses. Thus, in analogy to humans, we suggest early onset and seamless consecutive pregnancies to help reduce prevalence of this disease, better maintain a self-sustained captive population and improve animal welfare.

Figure 1. ‘Extended field of view’ ultrasound images of the vagina, cervix, and uterus of Indian rhinoceroses with and without reproductive tract tumour.

A. Extended sonogram of healthy vagina, cervix, and uterus. Beginning and end of the respective organs are indicated by the arrows underneath (←). B. Extended sonogram of vagina, cervix, and uterus with a single, large reproductive tract tumour present at the cranial aspect of the cervix (↓). C. Confluent, diffuse tumour present throughout the entire vagina and cervix. The organs wall and lumen are replaced by massive tumour overgrowth indicated by the circles.

Figure 2. Ultrasound images of reproductive tract tumours in Indian rhinoceroses.

A. Ultrasonographic appearance of reproductive tract tumours. Small and medium sized tumours appear as solid, dark, spherical structures. Large tumours may become necrotic indicated by high echoic centres. B. A vaginal tumour compresses the ureter above the bladder, causing partial obstruction and proximal dilation of the ureter.