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Dark Horse against a darkening sky

The Genetic Basis for a Horse’s Personality

By Christa Lesté-Lasserre

If you think you can make some generalizations about breed personalities, scientists say you could be right.

It’s time for some stereotyping: How would you describe the personality of a Thoroughbred? How about an Arab? Shetland pony? Appaloosa? Belgian Draft? Native working horses in Africa and Asia? If you think you can make some generalizations about breed personalities, scientists say you could be right.

Results from recent studies by a Japanese research group suggest there’s biologic evidence that a horse’s personality is based on his genes, and that these genes differ from one breed to another. What’s more, the researchers are even honing in on exactly where certain personality traits can be found on different breeds’ genomes.

The key is dopamine—a natural chemical in the nervous system—which appears to play an important role in how horses behave socially and develop personality, said Yusuke Hori, PhD candidate, researcher in the department of psychology at Kyoto University in Kyoto and at the Japan Society for the Promotion of Science in Tokyo.

Specifically, one particular dopamine receptor—the “D4” receptor (or DRD4), as scientists call it—has been previously shown to affect equine personality. So Hori and his fellow researchers set out to find the D4 gene in a variety of horses and then compare their findings across different breeds.

A 2005 study led by Yukihide Momozawa, PhD, at the University of Tokyo showed that a single nucleotide polymorphism in DRD4 appears to affect the individual differences in what he defined as a horse’s “curiosity” and “vigilance,” Hori said.

“Momozawa used Thoroughbreds in his study, so we analyzed the same gene (DRD4) by using samples collected from more horse breeds,” he said.

Hori’s team explored the genomes of 70 horses representing seven different breeds: the Thoroughbred, the Selle Français, the Criollo, three native Japanese working breeds, and one native Korean working breed.

They found that DRD4’s allele frequency (the proportion of a particular allele among all allele copies) of seemed to differ from one breed to another, Hori said.

“These differences could be the basis of breed differences in behavior, which would be really interesting,” Hori said. “But we need more studies to confirm this hypothesis.”

Even so, it’s important to note that personality is not a result of genetics alone, Hori said. “In general, personality is affected by not only genes but also environments,” he said. “So we have to keep in mind that genetic effects are partial.”

Nonetheless, recent studies in a variety of species, including humans, have shown that individual differences in genes could “partially affect the individual differences in personality or behavior,” he said.

The goal of the study is not to stereotype breeds, especially breeds that might be associated with difficult personalities, he said, but to help give a scientific basis that could lead to more customized training for different breeds according to their personalities. His research could also contribute to the way people interact with their equine partners.

“I hope these results will be a help to improve the relationship between horses and humans,” Hori said.

The study, “Breed Differences in Dopamine Receptor D4 Gene (DRD4) in Horses,” was published in the Journal of Equine Science of the Japan Society for Equine Science.