Horse Illustrated Magazine

Gray horses are found in many breeds, but it turns out their roots may be tied to one ancestor that lived thousands of years ago. An international team of scientists led by researchers at Uppsala University in Sweden has now identified the mutation causing the gray color trait in horses. According to the research, which was published July 20 on the Web site of Nature Genetics, gray horses carry an identical mutation that can be traced back to a common ancestor that lived thousands of years ago—probably an Arabian horse.

A gray horse is typically born black, bay or chestnut, but the graying process starts during the first year of life. As the horse ages, he may turn completely white, although his skin remains pigmented.

“It is a fascinating thought that once upon a time a horse was born that turned gray and subsequently white and the people that observed it were so fascinated by its spectacular appearance that they used the horse for breeding so that the mutation could be transmitted from generation to generation,” says Leif Andersson, who led the study.

The gray coloring is also very interesting from a veterinary point of view since the mutation also predisposes a horse for development of melanoma. According to the research, about 75 percent of gray horses older than 15 years of age have a benign form of melanoma that in some cases develops into a malignant melanoma. The research suggests that gray horses are more prone to the disease because of the gray mutation.

Regardless, gray horses will continue to be sought after and adored as they have for thousands of years.