There’s and old adage amongst horsemen that says a good horse is never a bad color. While that may very well be true, ask a group of horse owners what their favorite coat color is and you’re likely to get some pretty strong, and pretty different opinions.
For as long as mankind has been breeding horses, color has been almost as important a factor as conformation and temperament. There are entire breeds based upon color and coat patterns alone. As science has evolved bringing with it a greater understanding of color genetics, breeding for color has become both and art and a science amongst horse breeders.
The basics of equine coat colors are quite simple. Every color out there (with the possible exception of white, which geneticists are still studying) is a variation on either a red or a black base coat. These two colors will be referred to as ‘base’ colors for the rest of this article.
Every foal born has either a black, or a red base coat. If there are no modifying factors a foal with a black base coat will have a black body, mane and tail and will be referred to as black. A foal with a red base coat will have brown body, mane and tail and will be referred to as chestnut, brown or sorrel depending on the shade of the coat and/or the terminology of the breed registry to which the foal belongs. Of these two colors, black is dominant (meaning, if a red and a black gene are both present the red gene will be over ruled and the black gene will be expressed resulting in a black base coat) and red is recessive (which means it takes two red genes before a red base coat will be expressed, this makes red recessive but homozygous). Every other color out there is simply a variation on these two base coat colors. Variations in color are generally caused by one of two gene types: dilution genes, or modifier genes.
Dilution genes by their name explain the effect of their variation. There are four dilution genes: cream, dun, silver, and champagne. Dilution genes in combination with the horse’s base coat have different effects depending on the type of dilution, the color of the base coat, and the presence of other genetic variations. It is possible for a horse to carry more than one dilution gene, as well as other genetic variations, all of which combined can lead to very spectacular visual coat colors. Because it is such a common color, bay is often considered a ‘base’ color. However it is not. The bay coloration in horses (brown body with black points, mane and tail) is actually cause by the agouti modifier on a black base coat. However, because this is such a common color it will be referred to as simply ‘bay’ when we get to the discussion of the effect variation genes have on it.
The following are what we commonly see as the basic result of each dilution on either a red or black base:
Cream: Cream is a red-based dilution gene, meaning it affects the red base coat but not the black. It is a simple dominant, which means that if a horse carries the cream gene, it will express it. Because it only affects horses with a red base coat, black horses (who look unaffected) will sometimes produce a dilute foal giving the impression that the cream gene has skipped a generation. However, this is not the case. The cream gene produces the following results:
On a red base creates palomino: brown body color is diluted to a golden color, mane and tail are white. On a black base creates smoky black: very little, if any noticeable change horse remains black. On a bay horse creates buckskin: brown body color is diluted to a golden color, mane, tail and points remain black.
Dun: The dun dilution gene affects both red and black base coats. Dun is characterized by a lightening of the coat, and primitive markings, which include a dorsal stripe, leg bars and a shoulder stripe. On a red base creates red dun: the body coat is lighter that the head and legs, leg and shoulder bar range in color and quantity.
On a black base coat creates black dun or grulla: body color turns a smoky blue/grey color, legs and head remain dark, leg and shoulder bar range in color and quantity.
On a bay horse creates dun (this is the most common dun coloring): body comes in many shades but is generally a light tan or yellow, darker legs and head, leg and shoulder bar range in color and quantity.
Silver: The silver gene is a relatively recent discovery. The effect on different black base coats varies widely, and it can be difficult to identify. This dilution gene has no effect on red base coats. The effect of the gene generally results in a light to white mane and tail, dapples on the body (as the horse ages) and some dilution of the base color. This gene is a simple dominant, which means if it is present it will be expressed.
On a red base: no change
On a black base creates silver dapple/black silver: variety of colors ranging from a light silver dapple-grey to a dark chocolaty brown. Usually accompanied by a light to white mane and tail.
On a bay creates silver bay: the brown body color is not affected. Dilution of the black points varies from dark brown to a slate color. Usually accompanied by a light to white mane and tail.
Champagne: The champagne dilution effects both black and red base coats, and is a simple dominant. This is also a relatively new genetic discovery, and as such is still being studied. Common traits of the champagne dilution include: amber, green, or blue eye color, pink to a light brown colored skin, often with freckles, dilution of the coat color, and a metallic sheen to the coat.
On a red base coat creates gold champagne: golden body color with a flaxen mane and tail, often mistaken for palomino.
On a black base coat creates classic champagne: body color diluted to a smoky brown/black, mane and tail can be light or dark, often mistaken for grullo but lacks primitive markings.
On a bay creates amber champagne: body color is diluted to a golden color; points can remain dark or experience some dilution along with the body color. Mane and tail can also be diluted, or remain dark. Often mistaken for silver bay or buckskin.
Modifier genes include: bay, flaxen, grey, sooty/smutty, and mealy/pangare. Modifier genes also work in conjunction with base coat color and create different visual results depending on the base coat color and other genetic factors.
Bay modifier: As was described earlier bay, or the agouti modifier, only affects the black base coat. The body of the horse is brown, with the black restricted to the points, mane and tail. Bays come in a wide range of color including blood/red bays, and very dark black bays.
Flaxen modifier: The flaxen modifier is not as yet completely understood. It is believed that the flaxen modifier only affects horses with red base coats, and it is also believed to be recessive (which means that both parents must pass on the gene for it to be expressed). When it is expressed, the flaxen modifier caused a lightening of the mane and tail ranging from golden brown to pure white.
Grey modifier: Grey is often thought of as a color, not a modifier. However, the grey gene is a modifier that affects horses of all base coats, it also affects all other modifier and dilution genes. Grey is a simple dominant, and causes graying of all coat colors.
Sooty/Smutty modifier: The sooty modifier works on both red and black based horses by darkening random parts of the body, but most often darkens the towline of the horse affected. However, it also affects the shoulders, hips and face of some horses. In some horses to sooty modifier is expressed to such a point that the horse becomes so dark its true color is almost completely masked.
Mealy/Pangare modifier: The mealy modifier causes a lightening ranging from tan to white in the following areas: on or around the muzzle, around the eyes, along the underside of the belly, in the flanks, on the buttocks and behind the elbows.
Many horses express a combination of more than one modifier or dilution-gene creating both a beautiful coat, and an intriguing puzzle as science, breeders and horse lovers alike strive to solve the mystery that is color genetics!
