The genome of a domestic horse has been successfully sequenced by an international team of researchers.
The work, published in the journal Science, may shed light on how horses were domesticated.
It also reveals similarities between the horse and other placental mammals, such as bovids - the hoofed group including goats, bison and cattle.
The authors also found horses share much of their DNA with humans, which could have implications for medicine.
Horses suffer from more than 90 hereditary diseases that show similarities to those in humans.
"Horses and humans suffer from similar illnesses, so identifying the genetic culprits in horses promises to deepen our knowledge of disease in both organisms," said co-author Kerstin Lindblad-Toh, from the Broad Institute at the Massachusetts Institute of Technology (MIT) in Cambridge, US.
"The horse genome sequence is a key enabling resource toward this goal."
To generate a high-quality genome sequence, the researchers analysed DNA from an adult female thoroughbred named Twilight.
The horse's DNA was sequenced using capillary DNA sequencing technology (known as Sanger sequencing) to reveal a genome that is roughly 2.7 billion "letters", or nucleotides, in size.
In addition to sequencing the genome of a thoroughbred horse, the researchers also examined DNA from a variety of other horse breeds.
These included the American quarter horse, Andalusian, Arabian, Belgian draft horse, Hanoverian, Hokkaido, Icelandic horse, Norwegian fjord horse, and Standardbred breeds.
The team surveyed the extent of genetic variation both within and across breeds to create a catalogue of more than one million single-letter genetic differences in these breeds.
This is slightly larger than the genome of the domestic dog, and smaller than both the human and cow genomes.
So far, scientists have also sequenced the genomes of the platypus, mouse, rat, chimpanzee, rhesus macaque and, of course, human.
Horses were first domesticated 4,000 to 6,000 years ago. Over time, as machines have become the chief sources of agricultural and industrial muscle, those roles have shifted to sport and recreational activities.