Przewalski's Horse (Equus ferus przewalskii, Equus przewalskii or Equus caballus przewalskii, classification is debated), or /zɨˈvɑːlskiː/, etc. in English; also known as the Asian Wild Horse or Mongolian Wild Horse, or Takhi (Тахь), is the closest living wild relative of the domestic horse.
Most "wild" horses today, such as the American Mustang or the Australian Brumby, are actually feral animals, horses that were once domesticated but escaped and reverted to an apparently wild status. The Przewalski's Horse, on the other hand, has never been successfully domesticated and remains a truly wild animal today. There were once several types of equid that had never been successfully domesticated, including the Tarpan, and others. However, most have become extinct, with the Przewalski's Horse and various sub species of the Onager the only remaining truly wild horses in the world.
In the wild, Przewalski's Horses live in social groups consisting of a dominant stallion, a dominant lead mare, other mares, and their offspring. The patterns of their daily lives exhibit horse behavior similar to that of feral horse herds: Each group has a well-defined home range; within the range, the herd travels between three and six miles a day, spending time grazing, drinking, using salt licks and dozing. At night, the herd clusters and sleeps for about four hours. Ranges of different herds may overlap without conflict, as the stallions are more protective of their mares than their territory.
Stallions practice a form of scent marking and will establish piles of dung at intervals along routes they normally travel to warn other males of their presence. In addition, when a female in the herd urinates, the stallion will frequently urinate in the same place, to signal her membership in the herd to other males. The stallions can frequently be seen sniffing dung piles to confirm scent markings.
The native population declined in the 20th century due to a combination of factors, with the wild population in Mongolia dying out in the 1960s. The last herd was sighted in 1967 and the last individual horse in 1969. Expeditions after this failed to locate any horses, and the species was designated "extinct in the wild" for over 30 years.
After 1945 only two captive populations in zoos remained: in Munich and in Prague Zoo. The most valuable group in Askania Nova was shot down by German soldiers during occupation and the group in the USA had died.
In 1977, the Foundation for the Preservation and Protection of the Przewalski Horse was founded by Jan and Inge Bouman, which started a program of exchange between captive populations in zoos throughout the world to reduce inbreeding, and later starting a breeding program of its own. In 1992, sixteen horses were released into the wild in Mongolia, followed by additional animals later on. These reintroduced horses successfully reproduced, and the status of the animal was changed from "extinct in the wild" to "endangered" in 2005. However, they are classified as "extinct in the wild" by the IUCN Red List, as they have not been reassessed since 1996. The area to which they were reintroduced became Khustain Nuruu National Park in 1998.
The world's largest captive breeding program for Przewalski's horses is at the Askania Nova preserve in Ukraine. Several dozen Przewalski's horses were also released in the area evacuated after the Chernobyl accident, which now serves as a deserted de facto natural preserve. An intensely researched population of free-ranging animals was introduced to the Hortobágy puszta in Hungary; data on social structure, behavior, and diseases gathered from these animals is used to improve the Mongolian conservation effort.
Three animals from this program live in a 12 acre (5 hectare) paddock in the Clocaenog Forest in North Wales, UK, on the site of a former Neolithic or Iron Age settlement. They were introduced there in 2004. The Forestry Commission hopes they will help recreate scenes from the Iron Age when horses similar to these roamed Britain freely.
Another herd exists at The Wilds Wildlife Preserve in Cumberland, Ohio, USA. The small herd of about 17 individuals is kept in a large area shared with other Asian animals. A small population is also kept by the Smithsonian Institution at a facility near Front Royal, Virginia and in the Smithsonian National Zoological Park in Washington, DC.
Recent advances in equine reproductive science have potential to further preserve and expand the gene pool. In October, 2007 scientists at the Smithsonian Institution's National Zoo successfully reversed a vasectomy on a Przewalski horse — the first operation of its kind on this species and possibly the first ever on any endangered species. While normally a vasectomy may be performed on an endangered animal under limited circumstances, particularly if an individual has already produced many offspring and its genes are overrepresented in the population, scientists realized the animal in question was one of the most genetically valuable Przewalski horses in the North American breeding program.