Seal brown color (Photo 9) is described as black or dark color of the body and guard hair with a brown or tan area around the muzzle, eyes, groin, near the elbows, on the underbelly (especially in the girth region), and sometimes on the upper inside of the hind legs. These markings can be present in different horses at different intensities and in different combinations, and most frequently it is possible to observe on the horse’s muzzle and near the eyes. In fact, people frequently confuse seal brown with dark bay (see p. 12), and even experienced horse breeders can make errors. In addition among some horsemen circulates a myth that seal brown color does not exist, and such horses are simply very dark bay or strongly faded black horses.
In order to accurately determine seal brown color, it is necessary to remember the following characteristics:
Brown areas usually have rounded or oval outlines, clearly separated against the black or dark background. In dark bays, on the other hand, there is a smooth transition between the red, brown, dark brown, and then black color. It is especially easy to examine this on the muzzle above the nostrils.
Brown areas have a relatively bright, reddish color, but are seldom light red.
Unfortunately, color determination in this case is complicated by the fact that the seal brown color also can have shades, as observed in bays. The characteristics described above are accurate only for the darkest and most typical versions of seal brown. In addition, the skin and hooves are pigmented, the eyes dark hazel, the eyelashes black or dark brown. Foals are usually born looking similar to bay foals, but with noticeably darker legs. The horse develops the color’s characteristic phenotype only after baby hair is shed. Seal brown color is common in German Sport Horse breeds, Thoroughbreds, Standardbreds, and Russian Trotters.
CHESTNUT
Chestnut color is a relatively uniform red or brown color of the trunk, legs, mane, and tail (Photos 10 & 11). Shades can range from very light red, to close to apricot, to dark, to almost black (dark red and dark brown). The mane and tail in chestnut horses are usually of the same color as the body, but it is not unusual to see horses with brighter or darker guard hair. The skin and hooves are pigmented, the eyelashes red, eyes hazel.
Dark (liver) chestnut horses have dark orange or brown color of body hair. The mane and tail can be the same tone as the body or brighter (yellowish or even flaxen), or sometimes darker. Standard (average) chestnut horses are orange or red-colored. Guard hair can be the same tone as the body hair, or lighter or darker. Light chestnut horses have light carrot or almost yellow color of the body hair. This nuance is characteristic for the Akhal-Teke and Russian Don horses, and also for many draft breeds. The mane and tail are typically brighter than the body hair.
Chestnut horses with a whitish or almost white hair in the mane and tail are called flaxen chestnuts (Photos 12 & 13). The mane and tail usually change shade with seasons and can become lighter or darker, depending on the individual animal. I discuss flaxen chestnuts and specific information about heredity in more detail on p. 39.
It is extremely rare to encounter chestnut horses with brown, dark brown, or black color of the mane and tail, and it may be indicative of false red dun (see p. 26 and photos 14 & 15). This version of chestnut color is characteristic of the Karabakh, Russian Don, and Budyonny breeds. In addition, many Russian Don and Budyonny horses develop a golden gloss to their hair.
The darkest version of chestnut color is called liver chestnut (Photo 16). The mane and tail can be yellowish, the same shade as the horse’s torso, or almost black. This color can be distinguished from dark bay by the body and legs—they are black in a bay (see p. 14). There is also a very rare shade of dark liver chestnut color, which can be confused with black. In this case the tail and mane can range from white, to vivid red, to the same color as the horse’s trunk. This color can be found in Morgan horses, for example. Such horses can be identified as chestnut with the aid of DNA analysis.
The hair of chestnut horses can also fade; in such cases, a horse may look like he is covered with dust.
Chestnut foals are born red color with whitish legs and underbelly. Guard hair is often light. The foals become darker with age.
Chestnut color is common, surpassed in frequency only by bay. It is prevalent in the Arabian, Thoroughbred, Hanoverian, Budyonny, and Karabakh breeds, and some breeds have a characteristic chestnut shade, including Suffolk Punch and Russian Don horses. Chestnut color is encountered extremely rarely in Friesians, Percherons, Cleveland Bay, Orlov Trotters, Exmoor ponies, and Andalusians.
INHERITANCE OF BASE COLORS
Base colors in horses (black, bay, seal brown, and chestnut) are controlled by two genes: Extension and Agouti. The gene corresponding to the Extension locus is called MC1R (melanocortin-1 receptor). The “Wild” allele of this gene, designated “E,” is dominant and codes for the intact, normal receptor for the melanocyte-stimulating hormone. Upon binding of the hormone, the receptor leads to the synthesis of the black pigment eumelanin in melanocytes.
A recessive allele of the receptor is designated “e,” and in the homozygous state the horse can produce only a defective receptor. As a result the melanocyte-stimulating hormone cannot activate the production of black pigment and the cells switch to synthesize the red/yellow pigment pheomelanin.
Thus, genotype “EE” or “Ee” determines the presence of black hair, and genotype “ee” produces red. A DNA test is available to test for the “e” (red factor) allele. With the aid of this test it is possible to determine if there is a chance to obtain foals with red color—for example, from a black horse. The absence of the “e” allele in the genotype (EE) means that a horse is homozygous for the dominant allele; the presence of allele “e” in a single copy (Ee) indicates that the horse is heterozygous. A horse homozygous for the recessive “e” allele (ee) can only have a chestnut base color.
The dominant allele “A” of the gene Agouti codes for an Agouti-signaling protein (ASIP), which is an antagonist of the melanocyte-stimulating hormone, neutralizing its action in some areas of the body. In these areas there isn’t any black pigment production and the hair is red. In sections in which Agouti-signaling protein is not produced (the mane, tail, lower part of the legs, and ear rims), the pigment synthesis is switched to the black eumelanin and the hair in these locations is black. Thus, dominant allele “A” leads to the formation of the bay color. The recessive allele “a” of Agouti results in the lack of production of ASIP, and in a homozygous state (aa) does not suppress the synthesis of black eumelanin throughout the entire integument. Therefore an “aa” horse, which also has the genotype “EE” or “Ee,” will have a black base color. A phenotype effect of the Agouti gene appears only in the presence of allele “E,” and directs the synthesis of eumelanin in necessary quantities. The Agouti gene has no effect in an “ee” homozygous horse because there is only the red pigment produced.
At present there is a DNA test
