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Gene mutation makes horses hot to trot

Harness racing

Trotters have a diagonal gait (Source: grafficx/iStockphoto)


The discovery may also lead to a greater understanding of spinal injuries in humans.

Reporting in the journal Nature , researchers say the telltale gene was unearthed in the Icelandic Horse, a breed that famously likes to pace.

Pacing is a peculiar kind of equine gait, in which the legs on one side of the animal move forward at the same time.

It is particularly prominent among Icelandic horses, descendants of horses introduced to Iceland by the Vikings and recognised as a purebred strain that gives a smooth, sure-footed ride.

Building on earlier work on lab mice, a team led by Leif Andersson at Uppsala University and the Swedish University of Agricultural Sciences compared the genetic code of 70 horses - 40 that could pace and 30 that could not.

They discovered that there was a tiny change, of just one letter in the code, in a key gene known as DMRT3 in the 40 pacing horses.

DMRT3 controls a protein in nerve cells in the spinal cord that, Andersson believes, is crucial in the coordination of leg movements in vertebrates.

Just as surprising, says Andersson, is the finding that the mutation also occurs strongly among trotters, or breeds that are used for harness racing, in which the horse pulls a two-wheeled buggy called a sulky.

Diagonal gait

Trotters have a gait that is diagonal, meaning that the rear leg and foreleg that are diagonally opposite to each other move at the same time.

In trotting races, a horse is not allowed to gallop, otherwise it is disqualified.

"What we think this mutation is doing is that it inhibits the transition to the gallop," says Andersson. "That has some obvious applications in horse breeding."

The genetic variant is widely spread among a breed called the American Trotter, but is found far less frequently among a rival called the French Trotter, he says.

"French Trotters are famous for being often very strong, but they are also famous for sometimes having problems in keeping the trot. They don't keep a clean trot as much as American Trotters do, and we think the reason is that the breed does not have as high a frequency of the mutation."

Andersson said it was likely that further work would turn up other variants that influence horses' gait, but for pacing and trotting horses, the DMRT3 mutation was clearly of enormous importance.

The team have patented a DNA test to identify the DMRT3 variant, enabling horse buyers to spot an animal with a higher chance of success at harness racing.

But the discovery also has important implications for human medicine, says Andersson referring to fundamental research into paralysis.

"It is a really critical discovery because we have found new basic knowledge about how the spinal cord controls the movement of the legs."

Tags: animals, genetics, brain-and-nervous-system, mammals