The myostatin gene (MSTN) has attracted the attention of many racehorse breeders for its association with racing performance. But new research has revealed that this muscle-fiber-building gene could also impact performance in other breeds. In fact, it might even affect gaited horses’ ability to perform the very gaits they’re known for.

“It requires a lot of strength and stamina to carry a heavy rider while simultaneously presenting a nice form on a breeding field test (for gaited horses),” said Liesbeth François, a visiting PhD student from the KU Leuven Livestock Genetics research group, in Belgium. “As such, by influencing the type of muscle fibers, MSTN likely supports a horse’s ability to perform gaits of a certain quality.”

For example, the Icelandic horse’s famous four-beat tölt might benefit from the right kinds of muscle fibers as determined by MSTN, said François. While researchers have recently identified the “gaitkeeper” gene as being primarily responsible for a horse’s ability to tölt, François said MSTN also appears to play a role—probably in the way it affects a horse’s muscular ability to carry out such a physically demanding movement.

In their study, François and colleagues genotyped three segments of the MSTN gene in 195 Icelandic horses. The horses were mainly from Iceland and born between 1968 and 2006. They had all undergone breeding evaluations, in which breed experts judged their morphology and gaits.

The researchers found significant correlations between the horses’ build and performance and their MSTN genotypes as seen in the three segments tested, François said. For example, one variant of the MSTN, the “C” allele, is known to be more present in high-performance racehorses needing strong bursts of energy for short periods—mainly Thoroughbreds and Quarter Horses. However, Icelandic horses with high scores for morphology and movement had few C alleles, she said.

“It is possible that the low frequency of the C allele in Icelandic horses may be a result of the horses’ traditional use as mounts over long distances and as pack animals,” the study authors reported.

As far as the tölt is concerned, François said her study underlines the importance of recognizing the roles of numerous genes in any characteristic, including gaitedness. “Certain traits, such as the tölt, are not solely influenced by one major gene,” she said. “Instead, they are more likely the result of multiple genes with variable effects.”

Overall, the study reveals how this muscle-fiber gene has helped shape the Icelandic horse into the robust but fluid animal it is today. “The Icelandic horse was an important mode of transportation in a wild landscape with barely any real roads until the beginning of the 20th century,” François told The Horse. “Only horses were available to transport both goods and people over short or long distances.

“To make this difficult passage and cross rivers with dangerous currents, a strong and reliable horse was necessary,” she said. “In these circumstances people likely selected horses with a lot of strength and stamina, a unique combination of athleticism that is undoubtedly reflected in their genes.”

The study, “Conformation Traits and Gaits in the Icelandic Horse are Associated with Genetic Variants in Myostatin (MSTN),” was published in The Journal of Hereditary