It's Not Just in Their DNA: How Care Shapes a Horse's Future

When it comes to developing a great horse, how much credit goes to DNA and how much to the humans who raise them?

- MICHAELA JAYCOX, WITH DR. STEPHEN COLEMAN AND DR. GRANT FINLEY

Ask any breeder, trainer, or rider what makes a great horse, and you're bound to hear some version of this age-old debate: Is it nature, or is it nurture? Do elite horses rise to the top because of the blood in their veins—or the hands that raise and guide them?

For decades, breeders have worked to stack the odds in their favor by utilizing superior bloodlines and selectively breeding for traits such as athleticism, temperament, and conformation. But even the best genetics can be derailed by mismanagement. And, as two experts explain, sometimes nurture holds more power than we think.

Dr. Stephen Coleman, an equine geneticist at Colorado State University, and Dr. Grant Finley, a practicing veterinarian specializing in breeding and performance horses at Vetwerx Equine, offered their insights on the subtle and significant ways the environment interacts with genetics throughout a horse's life.

Genetics: Setting the Stage

Structure, athleticism, and temperament all begin in the DNA. But the story doesn't end there.

Traits are the measurable characteristics of an organism, Dr. Coleman explains, and their visible expression is called a phenotype.

“Coat color is a trait. Bay, chestnut, black—that's phenotype. And each phenotype has a genetic component associated with it.”

Simple traits tied to single genes—like HYPP or HERDA—can be predicted with confidence. However, when it comes to multi-gene traits, such as conformation, behavior, or movement, predictability becomes more complex.

“The simpler we make the thing we're evaluating, the more consistent we can be,” says Dr. Coleman. “The more complex it is, the more that Mendel’s laws of dominance, segregation, and independent assortment get mixed together. You get more variation, even among full siblings.”

Epigenetics:

Where Environment Meets DNA