Scientists have recently discovered why certain gray horses become entirely white as they age, while others stay a striking ‘dappled’ gray.
Researchers from Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) and Uppsala University in Sweden have gained insight into the phenomenon of some gray horses turning completely white over time, while others maintain a beautiful “dappled” gray appearance.
Published in the journal Nature Communications, the key factor lies in the number of copies of a specific DNA sequence found within the gray coat gene of each horse. Horses that experience “slow graying” possess a gene variant with two copies of the duplication, whereas “fast-graying” horses—those that will eventually turn white—have a gene variant with three copies.
“Some horses are born white due to a gene variant that directly causes this color; however, most white horses do not carry this gene variant,” explained Dr. Leif Andersson, a professor in the VMBS Department of Veterinary Integrative Biosciences and at Uppsala University. “Gray horses typically start life with regular coat colors—such as black or brown—that fade over time into gray or ultimately white.”
The distinction between having two or three gene copies impacts how quickly a horse turns gray and whether it ends up as gray or white.
“Certain horses destined to become completely white show signs of graying, such as gray eyelashes and tail hairs, within their first week of life,” Andersson noted. “In contrast, a ‘slow graying’ horse usually doesn’t display any gray signs until they are between 5 to 7 years old.”
While the coat color—be it gray or white—seems not to affect a horse’s athletic abilities or general health, it does increase their likelihood of developing melanomas, a type of skin cancer linked to the gray gene in horses.
“Horses that are ‘fast graying’ have a higher chance of encountering melanomas, whereas those classified as ‘slow graying’ show no significant increased risk,” Andersson stated.
The researchers are optimistic that this newfound knowledge about gray coat color and equine genetics will pave the way for additional studies aimed at preventing and treating melanomas in gray horses.
