Ambling - Heritability and Breeding

Heritability and Breeding

In most "gaited" breeds, an ambling gait is a hereditary trait. However, some representatives of these breeds may not always gait, and some horses of other breeds not considered "gaited" may have ambling-gaited ability, particularly with training. A 2012 DNA study of movement in Icelandic horses, harness racing horse breeds, and mice have determined that a mutation on the gene DMRT3, which controls the spinal neurological circuits related to limb movement and motion, causes a "premature 'stop codon'" in horses with lateral ambling gaits. This mutation may be a dominant gene, in that even one copy of the mutated allele will produce gaitedness.

A number of horse breeds have natural gaited tendencies, including the American Saddlebred, Icelandic horse, Missouri Foxtrotter, Paso Fino, Peruvian Paso, Racking horse, Rocky Mountain Horse, Spotted Saddle horse and Tennessee Walker The two-beat lateral pace is also sometimes classified with the ambling gaits as an "alternate" gait, and may be linked to the same genetic mechanism as the lateral ambling gaits. In order to pace at all, the horses studied were all homozygous for the DMTR3 mutation. But not all horses with the homozygous mutation could pace, suggesting other factors had to come into play for that gait to occur.

Of note is that the trotting bloodlines of the Standardbred, though distinct from the pacing bloodlines, also are homozygous for the DMRT3 mutation, suggesting that it not only affects lateral gaits, but inhibits the transition to a gallop. In the studies of Icelandic horses, those animals homozygous for the DMRT3 mutation scored poorly for their ability to both trot and gallop. Researchers concluded that breeders selected away from the mutation in horses bred for sports such as dressage, show jumping, and racing at a gallop.