All horses can canter, gallop, walk, and trot, but some can also move to different beats, ones that make for faster harness-racing animals and smoother riding by cowboys and other long-distance travelers. For horses around the world, the same genetic mutation—bred into the horses by humans—underlies these additional gaits , researchers report in the March issue of Animal Genetics. Some horses “pace,” a gait used in harness racing where the two feet off the ground at any one time are on the same side (shown above). Others, the so-called gaited breeds, amble, a fast walk characterized by having at least one foot on the ground at all times, but not necessarily three as in a true walk. The new research builds on work reported in 2012. At the time, scientists studying Icelandic horses known for a special gait discovered that they, as well as American Standardbred horses used in harness racing, share a somewhat shortened version of a gene called DMRT3.  The team showed that this gene, whose protein influences the activity of a bunch of other genes, helped control leg coordination in mice and suggested the mutation made the rhythm and order of footfalls more flexible. Now, the researchers have looked for this version, called gait keeper, in 4396 horses from 141 breeds from around the world. They find it in high frequencies in 68 breeds, which include all the gaited breeds as well as those used in harness racing. Further analyses indicated that this mutation arose relatively recently in equine evolution and was spread by horse breeders. Broader genetic studies are needed, however, to pinpoint where the mutation arose.
ScienceShot: Humans Spread Mutation That Smoothes a Horse's Ride