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Conservation of the Critically Endangered Persian Onager at the National Zoo

The Persian onager, a subspecies of Asiatic wild ass, is more closely related to the domestic donkey (E. asinis africanus) than to domestic horses (E. caballus). While scientists know the basic reproductive traits of the domestic donkey, little is known about the reproductive biology of onagers. Historically, subspecies of Asiatic wild asses inhabited thousands of acres including the steppes and deserts ranging from Saudi Arabia in the Middle East to as far west as Mongolia and China. Their range has shrunk to a small fraction of the original habitat. Remaining animals are now restricted to protected areas. Numbers of most subspecies have declined to a few thousand, with only a few hundred in some areas. The Persian onager is native to Iran. Their population is restricted to two areas in Touran and Bahram-e-goor with estimates of no more than 500 animals left in the wild. Loss of habitat, poaching, competition with domestic livestock and the effects of war and civil unrest threaten the remaining populations.

Animals at zoos and breeding facilities offer scientists an important source of basic information on normal physiology. These animals also represent a potential source of healthy animals for reintroduction to their natural habitat. However, there are fewer than 70 onagers in zoos in North America. Due to sub-optimal management practices, many of these animals are reaching the end of their reproductive years, and the population is no longer self-sustaining. Therefore, establishing a healthy population of onagers in zoos as an insurance collection is critical for the long-term survival of this species.

Assisted reproductive technologies such as artificial insemination have great potential for increasing breeding efficiency and genetic variability in small populations. Furthermore, genome resource banks (frozen reserves of sperm and/or eggs) also can serve as insurance policies against unforeseen catastrophes, such as disease, poaching, and pandemics. However, very little is known about onager reproduction and successful implementation of these technologies requires a thorough understanding of the reproductive biology of both the male and female onager.

Scientists are working on a series of studies that will increase substantially our understanding of the reproductive biology of onagers. The goals of these studies are to:

  • Determine normal reproductive hormone levels and evaluate fertility in onagers in zoos and breeding facilities across North America, by evaluating historical records, comprehensive hormonal and behavioral observations, breeding soundness examinations (rectal palpation, ultrasonography, uterine biopsies, physical examination), and seasonal evaluations of sperm production and quality in males
  • Develop safe and effective methods for semen collection from male onagers, including best practices of animal handling and/or anesthesia regimens; and
  • Evaluate how sperm react to being frozen with the eventual goal of establishing a genome resource bank (GRB)

This project is part of a major collaborative effort of the Conservation Centers for Species Survival (C2S2), a consortium that facilitates cooperation among zoological institutions. This consortium is comprised of the Fossil Rim Wildlife Center (Glen Rose, Texas), San Diego Wild Animal Park (Escondido, CA), The Wilds (Cumberland, Ohio), White Oak Conservation Center (Yulee, Florida) and the National Zoo's Conservation and Research Center (Front Royal, Virginia). All partners have large land resources and specialized animal handling facilities with the potential for maintaining and studying ungulate species (animals with hooves). The C2S2 institutions have developed a plan for cooperation to promote global conservation of endangered ungulates. The consortium also has identified the Persian onager and the Przewalski’s horse as priority species for research. Current research will help us understand the biology of the onager and use that new knowledge to develop self-sustaining populations to the benefit of species in zoos and in the wild.