Chestnut. Mahogany. Joint. Bay. These terms are all used to describe the color of a horse’s coat and they are all shades of brown. In fact, you have probably noticed that the vast majority of horses are some variation from light to dark brown. Have you ever wondered why?
It all comes down to genetics.
According to Dr. Annette McCoy, an equine surgeon at the University of Illinois Veterinary Teaching Hospital, the staining of horses is an example of “simple inheritance” in that the color we see is determined by a single gene. The dam and the sire each give a dominant or recessive version of the trait. The resulting foal then shows the dominant version unless both parents give a recessive copy of the gene. In this case, the foal will show the recessive trait.