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EquiGenetic Relevations

Gray (the Gray Gene)

The gray gene is not an independent color but the result of a mutation in the STX17 gene, which overlays the base color of a horse and causes it to gray prematurely. The base color of the horse is irrelevant. The gray gene is a dominant gene. This means that a heterozygous gray horse passes on the gray gene to 50% of its offspring, and a homozygous gray horse passes it on to 100% of its offspring.

Genetic Code

The genetic code for Gray is as follows:

  • n/n = no Gray present
  • N/G = heterozygous Gray present
  • G/G = homozygous Gray present

n/n Genotype: Horses with the n/n genotype do not have the gray gene and cannot pass it on to their offspring.

N/G Genotype: Horses with the N/G genotype have a classic graying pattern. They can pass this gene to their offspring with a 50% probability. Crossings with an n/n genotype have a 50% chance of producing a gray foal.

G/G Genotype: Horses with the G/G genotype have the classic graying pattern. They will pass this gene to all their offspring. Crossings with any genotype will exclusively produce gray offspring.

Discovery and Genetic Basis

The gray gene was discovered by a team of Swedish researchers led by Leif Andersson at the University of Uppsala. These researchers found that the mutation is influenced by four different genes and that all gray horses likely share a common ancestor.

Graying Process

The premature graying process is usually completed between the first and tenth year of life. It has been observed that the graying process takes longer in darker horses, such as black horses, while light base colors like chestnut or lightened horses gray faster.

Variants During the Graying Process

During the graying process, various gray variants can appear depending on the base color over time. These variants include the dapple gray, which shows dark-rimmed circles on a light coat; the iron gray, which is born black and gradually gets more white hairs; and the rose gray, which gets lighter each year.

Appearance After Graying

After complete graying, there are different appearances of gray horses. Some become completely white, while others show the pattern of a fleabitten gray with many small black spots or a speckled gray with many small reddish or brown spots. There are also grays with blood marks or bloody shoulders, where parts of the body, often on the shoulder or neck, do not gray out and remain brown or red with large spots. Another form is the porcelain pinto, a pinto that grays out.

Health Aspects and Risks

The gray gene is also associated with the development of gray melanomas, benign skin tumors that occur in about 80% of all gray horses over 15 years old and can develop into malignant tumors. These melanomas are often not visible externally and grow inside the horse. Scientists have found that homozygous grays have the highest risk for melanomas. Due to this high melanoma rate, some breeders classify grays as a defect breed.

Distribution and Frequency

Grays are particularly common in certain breeds. These breeds include the Camargue horse, Percheron, Lipizzaner, Thoroughbred Arabian, and P.R.E. It has been found that homozygous grays gray out faster than heterozygous grays.

 
The graying process of the Purebred Arabian gelding Maron over the years. Born with a bay base color to two gray parents, the gray gene became clearly visible with the loss of his foal coat. Maron is heterozygous gray and a typical rose gray. Now 12 years old, he is almost completely gray, with only a few gray strands and isolated gray spots on his legs.
 

The graying process of the Purebred Arabian gelding Maron over the years. Born with a bay base color to two gray parents, the gray gene became clearly visible with the loss of his foal coat. Maron is heterozygous gray and a typical rose gray. Now 12 years old, he is almost completely gray, with only a few gray strands and isolated gray spots on his legs.

Jannes, a Welsh A stallion with exclusively gray ancestry over many generations, was born bay and had already grayed significantly as a yearling. By the age of 4, he was completely gray, suggesting that he is homozygous gray.

Malva, a beautiful Lipizzaner mare, displays the typical spots of a speckled gray.

Malva, a beautiful Lipizzaner mare, displays the typical spots of a speckled gray.