DNA analysis shows thoroughbreds have British as well as Arabian roots

The favorite, Big Brown, uses an explosive finishing kick to lead he and jockey Kent Desormeaux to a 4 3/4-length victory at the 134th Kentucky Derby, becoming the first horse since 1929 to win from the 20 post.
Monday, October 18, 2010; 5:37 PM

Where thoroughbreds came from

Sleek, speedy, and spirited, thoroughbred horses arose from Arabian stallions more than three centuries ago. But whose mares birthed these noble steeds? A new genetic analysis suggests that thoroughbred foremothers hailed from Ireland and Britain.

In the late 1600s and early 1700s, three stallions imported by British aristocrats became the forefathers of today's thoroughbreds: the Godolphin Arabian, Darley Arabian and Byerley Turk. The three came to England on different paths: One was purchased in France, one acquired in Italy, and the third captured in 1686 from a Turkish officer in a battle at Buda, part of today's Budapest. "We know their names and we have paintings of them," says Mim Bower, an archaeogeneticist at the University of Cambridge in England. Breeders also know a lot about the horses' descendants, as they carefully recorded the lineages over the centuries.

But no one kept track of the moms. Breeders thought that the important parent was the stallion, says Bower, and that any mare would do as a mother. Many breeders assumed that the original mothers were native British horses. But in the early part of the 20th century, some breeders came to believe that thoroughbreds' mothers were also Arabians, probably because this idea seemed more aristocratic. Bower and her colleagues set out to settle the debate with genetics.

They focused on DNA housed within mitochondria, which is passed down only by the mother and can be linked to particular geographical regions.

The researchers analyzed DNA from about 300 thoroughbreds and nearly 2,000 other horses from across Europe and Asia. Most of the sequences came from a genetic database, but the researchers also asked horse owners to provide samples from their animals. "We ask people to pull hair," says Bower. The team then sequenced short stretches of DNA extracted from the tissue attached to the hair.

The thoroughbreds' mitochondrial DNA sequences were closest to those of native Irish and British breeds, including the Connemara. There was a hint of other ancestries, including Arabian, but thoroughbred moms most likely hailed from the British Isles, the researchers reported online in Biology Letters.

- Helen Fields

This article comes from ScienceNOW, the daily online news service of the journal Science, which can be read online here.sciencemag.org.

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