09.03.2023: Not all rhinos are the same, as a recently published study by the University of Veterinary Medicine in Vienna clearly demonstrates. Individual species of rhinoceros differ considerably in terms of gestation length and hormone profiles during pregnancy. The new findings are of great importance for the survival of rhinoceros species threatened with extinction.
An extensive study conducted by the University of Veterinary Medicine Vienna, in cooperation with the Leibniz Institute for Zoo and Wildlife Research in Berlin and involving data collected over the course of three decades, investigated the reproductive cycle and pregnancy in three rhinoceros species kept in European zoos: the black rhinoceros (Diceros bicornis), the white rhinoceros (Ceratotherium simum) and the greater one-horned or Indian rhinoceros (Rhinoceros unicornis).
The research team collected hormone profiles from rhinos kept in more than 35 European zoos as part of pregnancy diagnoses. The results were evaluated, summarized and published in the scientific journal General and Comparative Endocrinology.
Important insights into pregnancy and length of gestation
The comparative analysis provides significant new insights into the hormone profiles during pregnancy and the gestation length of the three rhinoceros species. First author Franz Schwarzenberger from the Institute of Physiology and Pathophysiology at Vetmeduni: “We found equally pronounced individual differences in the onset of placental progestogen production and in mean gestation length. The average values of pregnancy duration for black, Indian and white rhinoceros were 460, 480 and 504 days, respectively. The average values of gestation length vary by about seven weeks within species.”
The seasons have a major influence on the duration of gestation, which, as Schwarzenberger determined from the data, is significantly influenced by the daylight hours at the time of birth: “Gestation is about one week shorter when the birth occurs in summer as opposed to winter.”
Research and breeding programmes essential for rhino survival
The rhinoceros family (Rhinocerotidae) comprises five extant species. These are native to Africa and Southeast Asia (Indonesia). All rhino species are hunted by poachers and, according to the IUCN Red List of Threatened Species maintained by the International Union for Conservation of Nature, are either critically endangered, vulnerable or near threatened. The protection of wild populations and captive breeding programmes are essential measures to ensure the conservation of rhinoceros species.
Captive populations are also crucial for studying the reproductive physiology and endocrinology of rhinos. The implementation of new physiological findings in internationally coordinated breeding programmes has already been instrumental in significantly increasing the number of reproducing rhinoceroses in zoos in recent decades.
The article “Comparative analysis of gestation in three rhinoceros species (Diceros bicornis; Ceratotherium simum; Rhinoceros unicornis)” by Franz Schwarzenberger and Robert Hermes was published in General and Comparative Endocrinology.