What Are Horse Blood Marks?

A blood mark is a type of marking found only on flea bitten gray horses.

The area on the horse that constitutes the blood mark is not gray like the rest of the horse: Instead, it is some other color. Commonly, the blood mark areas are red (chestnut) which gives the marking its name.

Below: A flea bitten gray horse with blood marks on the neck and shoulder.

While blood marks can appear anywhere on a horse's body they are perhaps best known for appearing on the shoulder area, and are therefore sometimes also called "bloody shoulder marks." They can be called a "blood mark" or a "bloody shoulder mark" no matter where they are located.

A blood mark on a horse is usually considered to be somewhere between unusual and rare.

According to the book "Equine Color Genetics" by D. Phillip Sponenberg blood marks might increase in size as a horse ages:

"......An extremely rare occurrence is in Fig. 105, which shows patches of red color growing into the coat of a grey horse. These patches are called blood marks and can become progressively larger, resulting in a very aged grey horse that appears uniformly red."

Below: A blood mark on the side and belly of a gray horse.

Horse Blood Marks and The Color Gray

Blood marks are unique to flea bitten gray horses. If you need a refresher on gray horse coloring here is a quick overview:

• A gray horse has colored body hairs that are mixed in with white hairs.
• Most commonly, the colored body hairs are black so that when they are mixed with the white hairs the horse displays a characteristic gray color.
• As a gray horse ages the colored hairs lose their pigmentation and the horse fades to a lighter and lighter gray color. Ultimately, the horse may appear to be white.
• Flea bitten grays have dark specks scattered over a lighter base color of white. This is opposed to dapple grays which have rings of gray throughout the coat; and steel grays which are a smooth blend of dark hairs and light hairs.

You can read more about gray horses here: How To... Recognize Horse Colors - Page 1.

The blood mark areas on a horse are not gray. As stated above they are some other color, most commonly red (chestnut).

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Blood Marks On Horses and "Somatic Mutations"

To better understand blood marks on horses it's handy to know they are a "somatic mutation." What is a somatic mutation?

• In mammals, a somatic cell is a cell that makes up the components of an animal's body (for example: skin, bones, blood, and more). A somatic cell is not responsible for reproduction (those kinds of cells are called "germ" cells).
• A mutation is a process that changes the DNA sequence of a gene. Mutations are considered to be natural, but not the norm. Some mutations are harmful while others are not.
• Somatic mutations, then, are mutations in the cells that make up the components of the body but do not include cells that can reproduce (germ cells). Somatic mutations are acquired at some point after conception, anywhere from in the womb to years after birth. They cannot be passed on to the next generation. Therefore, a horse with a blood mark may or may not produce progeny with a blood mark, but it is a characteristic that cannot be bred for.

Blood Marks and the Bedouin Mare

Blood marks, although an unusual marking on any horse, are traditionally associated with the Arabian breed. The breed originated in the great, inhospitable deserts of the Middle East and have long been prized by many different people, including the Bedouins who have made their lives in these deserts for centuries.

There is a legend about an Arabian mare owned by a Bedouin chieftain that describes how the very first blood mark came about. The following version is from Arabian Horse World magazine.