Przewalski's horse in the context of "Equus ferus"

The wild horse (Equus ferus) is a species of the genus Equus, which includes as subspecies the modern domesticated horse (Equus ferus caballus) as well as the endangered Przewalski's horse (Equus ferus przewalskii, sometimes treated as a separate species i.e. Equus przewalskii). The European wild horse, also known as the tarpan, that went extinct in the late 19th or early 20th century has previously been treated as the nominate subspecies of wild horse, Equus ferus ferus, but more recent studies have cast doubt on whether tarpans were truly wild or if they actually were feral horses or hybrids.

Other subspecies of Equus ferus may have existed and could have been the stock from which domesticated horses are descended. Przewalski's horse had reached the brink of extinction, but was reintroduced successfully into the wild. The tarpan became extinct in the 19th century, but is theorized to have been present on the steppes of Eurasia at the time of domestication. Since the extinction of the tarpan, attempts have been made to reconstruct its phenotype using domestic horses, resulting in horse breeds such as the Heck horse. However, the genetic makeup and foundation bloodstock of those breeds is substantially derived from domesticated horses, so these breeds possess domesticated traits.

Nikolay Mikhaylovich Przhevalsky (or Przewalski or Prjevalsky; 12 April [O.S. 31 March] 1839 – 1 November [O.S. 20 October] 1888) was a Russian geographer and a renowned explorer of Central and East Asia. Although he never reached his ultimate goal, the city of Lhasa in Tibet, he still travelled through regions then unknown to Westerners, such as northern Tibet (modern Tibet Autonomous Region), Amdo (now Qinghai) and Dzungaria (now northern Xinjiang). He contributed substantially to European knowledge of Central Asian geography.

Przhevalsky described several species previously unknown to European science, such as Przewalski's horse, Przewalski's gazelle, and the wild Bactrian camel, all of which are now endangered. He was also a mentor of the explorer Pyotr Kozlov.

Species reintroduction is the deliberate release of a species into the wild, from captivity or other areas where the organism is capable of survival. The goal of species reintroduction is to establish a healthy, genetically diverse, self-sustaining population to an area where it has been extirpated, or to augment an existing population. Species that may be eligible for reintroduction are typically threatened or endangered in the wild. However, reintroduction of a species can also be for pest control; for example, wolves being reintroduced to a wild area to curb an overpopulation of deer. Because reintroduction may involve returning native species to localities where they had been extirpated, some prefer the term "reestablishment".

Humans have been reintroducing species for food and pest control for thousands of years. However, the practice of reintroducing for conservation is much younger, starting in the 20th century.

The tail of the horse and other equines consists of two parts, the dock and the skirt. The dock consists of the muscles and skin covering the coccygeal vertebrae. The term "skirt" refers to the long hairs that fall below the dock. On a horse, long, thick tail hairs begin to grow at the base of the tail, and grow along the top and sides of the dock. In donkeys and other members of Equus asinus, as well as some mules, the zebra and the wild Przewalski's horse, the dock has short hair at the top of the dock, with longer, coarser skirt hairs beginning to grow only toward the bottom of the dock. Hair does not grow at all on the underside of the dock.

The tail is used by the horse and other equidae to keep away biting insects, and the position and movement of the tail may provide clues to the animal's physical or emotional state. Tail carriage may also be a breed trait. Tails of horses are often groomed in a number of ways to make them more stylish for show or practical for work. However, some techniques for managing the tails of horses are also controversial and may constitute animal cruelty.