Coat patterns of white hairs (non-pigmented) are genetically determined and applied over the modified base coat color. In other words, they are secondary to the red and black base genes and the agouti (bay), gray and dilution (lightening) genes. Please see the coat color section before diving into white patterns.
White hairs occur where pigmenting is not allowed, and how this happens has been determined in several white patterns but is still debated in others. The patterns distribute into the following categories, described after this list:
White markings are hair without pigmentation and uniquely identify individual horses. These do not change over time or with the amount of sunlight. The skin is also pink (without pigment) underneath, but in some horses, the white hairs can overlap or underlap onto the pigmented skin (sabino pattern).
White markings appear on the face as a star between the eyes, a stripe along the length of the face, a snip between the nostrils to the upper lip, a lower lip, or any combination of these, such as star, snip and lower lip with no stripe. White markings also appear on any number of limbs as distal white spots on the coronary band (distal spots), a white band around the coronet above the hoof, extending from the coronet to below the fetlock (white pastern), from the hoof to just above the fetlock (sock), from the hoof to halfway up the cannon bone (half stocking), or to just below the carpus or tarsus (stocking). They can even go above the knee and hock and are said to be “stocking and knee.” Horses with white extending beyond the knee or hock are usually pinto horses.
White markings are used on official papers to help identify individual horses because each white marking is unique to every horse. I was “infamous” at the New York - Canadian border because I drew these white markings in detail and accurately on the travel papers. One of my clients traveling into Canada told me that the inspector saw her papers made out by me and declared, “You’re good with these horses,” but went into the large van to thoroughly inspect the other horses with papers made by another vet.
Roaning is when there are hairs that are not pigmented and are therefore white. They are evenly mixed with the colored hairs throughout the body except for the head. The hairs of the head are either a solid color or look darker than the rest of the body. The line between the head and the neck is clear behind the ears down to the throat. They are also roan at birth, while a gray horse only becomes gray over time and affects all body hairs, just like in older humans.
Red Roans or Strawberry Roans are over the base coat color of red. Bay Roans are over a base color of red plus the agouti gene making the horse bay. Blue Roans are over a base color of black. Dun stripes can be seen on Roans as well.
Pinto horses have white patches on their solid-colored body. The white hairs are not evenly mixed (roaning) but have distinct white areas with one exception. When a white patch contains colored hairs, and only this patch displays roaning, the horse has the sabino pattern.
Pintos fall into two color groups:
Pintos come in four patterns:
Leopard Complex Markings
The leopard complex is the definition of a group of genes that create a variety of distinct white markings characteristic of Appaloosa and other breeds of horses worldwide. The varieties include:
White Horse Markings
The white horse pattern affects all hairs turning them white, plus the underlying skin is pink. The pink skin is the difference between a progressively graying horse and a permanent white horse. In addition, they are born white and remain this color throughout life. Their eyes can be either brown or blue.
White horse genetics are unclear because to be a white horse, a dominant gene is needed. However, if the gene is dominant, there would be more white horses, but they are rare. Therefore there must be other factors involved. Some suggest there is a link with the sabino gene. Sadly, many foals born white also have a mutation in the gene that forms the colon. A foal with this mutation dies from the “Lethal White Syndrome” or “Overo Lethal White Syndrome.” Offspring of overo matings, where one parent is a carrier of the mutation, never survive because the digestive tract is blocked. There is a DNA test to identify these carriers.
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