Genetic Testing for Coat Color in Horses Reviewed

That "Ole gray mare" in the pasture was likely highly selected for during the domestication of horses and, according to some researchers, resembles her forefathers little in terms of coat coloring.

While many wild animal species are colored relatively uniformly, our domestic horse stock show "a broad variety of coat color patterns," wrote animal geneticists Stefan Rieder from the Swiss College of Agriculture in Zollikofen, Switzerland, in a recently published review article on the history and commercial applicability of the genes responsible for coat colors in horses.

One theory explaining this "horse of a different color" phenomenon is that, historically, only a few coat colors might have been appropriate for survival in the wild. For example, horses of a certain color could have been better camouflaged, considered a more appropriate mate, have more tolerance to certain pathogens, or better adapt to the environment than horses of other colors.

During domestication, however, human preferences resulted in the selection of horses with selected colors, resulting in horses with stunning and sometimes elaborate patterns.

Since coat coloring in horses is easy to see and generally follows simple Mendelian genetics (dominant and recessive genes), coat color genes were among the first genes to be studied systematically.

"As a result of the number of genetic tools developed during the past decade, horse coat color tests have been designed are now commercially available for some of the basic phenotypes," wrote Rieder.

Some of these tests are commercially available and allow breeders to:

  • Verify segregation within certain pedigrees;
  • Select specific coloring based on market demand or studbook policies, and
  • Avoid inherited disease associated with some colors (such as overo lethal white syndrome).

Rieder noted additional research is needed to "fully differentiate and precisely define the heterogeneity of horse color phenotypes (shades such as darker chestnut or darker bay, flaxen mane and tail, seasonal coat color change, the problem of phenotypes that resemble one another but are genetically different, etc.)."

The review article, "Molecular tests for coat colours in horses," was published in the December 2009 edition of the Journal of Animal Breeding and Genetics. The abstract is available on PubMed.

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