Last year, The Horse reported that scientists had discovered a single gene mutation that was responsible for the lateral ambling/pacing gaits of gaited breed horses such as Saddlebreds, Icelandics, and Standardbreds.

But new research has revealed that the same mutation could actually be responsible for success in trot racing, too. Despite the irony, it appears that this DMRT3-gene mutation, called the Gait Keeper gene, is associated with better performance at harness tracks.

“It seems that besides enabling ambling and pacing, this Gait Keeper gene seems to also inhibit transition from the trot to the gallop,” said Leif Andersson, PhD, researcher at Uppsala University and the Swedish University of Agricultural Sciences. Maintaining a trot at high speeds without breaking into a gallop is a critical component of harness racing.

“We’ve already seen that Icelandic horses that are homozygous for the Gait Keeper mutation (meaning they have inherited the mutation from both parents and, thus, have two copies) are worse in the gallop than Icelandics that only carry one copy of the mutation,” Andersson said. “So we think that the Gait Keeper promotes the trot in favor of the gallop.”

Andersson and colleagues investigated breeding and performance records of two breeds of trot-racing horses—the Standardbred and the Nordic Trotter (a heavier, draft-type trotting horse). They also analyzed these breeds’ DNA, with birth dates going back to 1950.

They found that trot-racing horses that were homozygous for the Gait Keeper gene were faster, won more races, earned more winnings, and had cleaner trots than horses with no copy of the gene (wild-type), Andersson said. In fact, Nordic Trotters homozygous for the Gait Keeper gene earned twice as much in winnings over their lifetimes than wild-type Nordic Trotters, he said.

Homozygous Standardbred horses also had better “estimated breeding values” (EBV), as determined by independent criteria within the breeding industry (which do not take DNA into consideration).

However, with progressing age, some of the heterozygous Nordic Trotters (those with a single copy of the Gait Keeper mutation) performed as well as, or even better than, the homozygous ones, Andersson added. “It could be that these heavier horses somehow benefit from being heterozygous as they get older,” he said.

But if this Gait Keeper gene promotes gaitedness, why aren’t these horses pacing instead of trotting? “Many have the ability to pace,” Andersson said. “And in fact the American Standardbred pacer started out as a trotter. But about 50 years ago they found out that some of the Standardbreds preferred to pace, and so they split the population.”

Even though many of the trotters are homozygous for the Gait Keeper gene, that doesn’t mean they necessarily prefer to pace, he added. “Locomotion in horses is not the effect of a single gene, but of many genes,” he said. “The Gait Keeper mutation is crucial and has the main effect, but other genes—as well as training—will come into play in encouraging the horse to pace or not.”

Even so, the Gait Keeper gene appears to be essential for a horse to be able to amble or pace, he added. “We have not come across a single horse pacing that does not have this mutation,” Andersson said.

In the future, Andersson’s team hopes to investigate genetic differences between American Standardbred trotters and American Standardbred pacers, he said.

The study, “The DMRT3 ‘Gait keeper’ mutation affects performance of Nordic and Standardbred trotters,” was published in the Journal of Animal Science