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Scientific Differences of Horses and Zebras

Zebras, although commonly thought of as striped horses or ponies, are separate species from the domestic horse or Equus caballus. But the two species can interbreed and produce sterile offspring known as "zorses" or "zonies." Zebras share more physical similarities with donkeys and wild asses than they do horses or ponies. Zebras and donkeys can also produce offspring, called "zonkeys," but these foals are also sterile.

Chromosomes
- All cells contain chromosomes, consisting of proteins and a double-helix DNA strand. Zebras and horses contain different numbers of chromosomes in their DNA. Horses and ponies have 64 while zebras contain much fewer, depending on the particular species. Equus zebra or the mountain zebra contain 32; Equus burchelli or Burchell's zebra contain 44 and Equus grevyi or Grevyi's zebra contain 46, according to "The Horse" by James Warren Evans.
Geography
- Both zebras and horses share a common ancestor, the Hyracotherium or "eophippus." It developed in what is now North America, but all equines disappeared from the Americas 10,000 years ago. No equine species would return to North or South America until European colonists brought horses and donkeys with them, beginning in Columbus' second voyage in 1493. Zebras only developed in Africa, while horses colonized Asia and Europe. Horses never took hold in Africa, but zebras did. Zebras tolerate the punishing environment of Africa far better than domestic horses or ponies.
Species
- Horses and ponies come in many breeds, which differ considerably in size, color, leg length and musculature, but all are members of one species, Equus caballus. In contrast, zebra have three species -- not breeds. Species produce fertile offspring when they breed and contain a certain number of chromosomes in their DNA. Breeds, which occur only in domestic animals like horses and not wild animals like zebras, produce fertile offspring that closely resemble their parents, but the offspring can mate with other breeds.
Conformation
- Horses have withers; zebras don't.
  
  Zebra body conformation more closely resembles donkeys than horses. Zebras lack withers, which are noticeable humps at the point of the shoulder. Withers help keep saddle in place on horses. Zebras also have longer ears than horses or ponies. While horses neigh and whinny, zebras vocalize in a similar manner to donkeys and wild asses.

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