target="_blank" rel="nofollow" href="#ulink_a3372fc1-418b-5276-8a5f-6ca59124795f">p. 19), and their primitive markings have a rusty or dark yellow color (Photo 42). The mane and tail can be practically all white with only the middle part of the tail containing colored hair as a continuation of the dorsal stripe.
One of the rarest colors in this group is double cream dilute (Ccr/Ccr) combined with the Dun gene. Such horses have a cream body color with a pale caramel dorsal stripe and zebra bars, and also pink skin and blue eyes (sometimes called wall eyes or china eyes). Dun horses carrying one Cream Dilution gene often have light-brown eyes.
Another rarity is the smoky black plus Dun gene color (smoky grullo). Visually it is closest to light grullo color with a yellowish tone (see p. 24), but it is impossible to distinguish the two colors without DNA testing. Such horses have dirty-brown or dirty-ashy, yellowish color, lighter toward the underbelly, and the mane, tail, and lower part of the legs are dark brown (Photos 43 & 44). They have a remote resemblance to faded black (see p. 11). Foals are born an ashy color that is lighter than grullo.
These colors are all fairly rare, and when found, are often in the Norwegian Fjord, Quarter Horse, and Bashkir Horse breeds.
Inheritance of Colors Determined by the Dun Gene
The dun colors are controlled by a dominant allele of the Dun gene (abbreviated as Dn+). This allele is considered the “Wild” version of the gene, while its mutant form (nd2, which means non-dun2) in a homozygous state defines the usual, ordinary non-dun colors. The result of its action is dilution of eumelanin, resulting in bluish or ashy hair color, and pheomelanin, resulting in light red, apricot, or pale caramel. However, the mane, tail, head, and lower part of the legs are diluted to a lesser degree, which may indicate the involvement of a temperature-sensitive biochemical mechanism. An integral part of the action of the Dun allele is the manifestation of primitive markings, and these have an unclear mechanism of formation.
According to a hypothesis made by Nancy Castle (2008), primitive markings are created in all horses during embryogenesis. However in color-diluted horses carrying the Dun gene, the markings are visible, whereas in non-Dun-gene horses—due to a darker background—these markings are invisible. Castle bases her theory on the fact that you can observe primitive markings in foals that disappear as the animal ages. In general, the color of a horse darkens with maturity, and it is possible that primitive markings remain present. In support of this hypothesis is the presence of such markings on adult horses that are not dun. Such horses are called false duns (see p. 78). The specific mutation of the Dun gene responsible is abbreviated “nd1” (non-dun1). There is a DNA test for the Dun gene. The hierarchy is Dn+ > nd1 > nd2.
Table 4.
| Primary Color | Dn+ |
|---|---|
| Bay | Bay Dun |
| Black | Grullo |
| Seal Brown | Brown Dun |
| Chestnut | Red Dun |
| Buckskin | Dunskin |
| Palomino | Dunalino |
COLORS DETERMINED BY THE SILVER GENE
The colors of this group (Z) were defined rather recently, at the beginning of the twenty-first century. Understanding the true distribution of these colors is difficult because they are rare, although apparently this dilution is present in quite a few different breeds. Color identification in doubtful cases should be guided in part by whether or not a color has shown to be present in a specific breed. Therefore, I feel it necessary to provide a list of breeds in which the Silver gene occurs at the beginning of our discussion. The list includes the: Rocky Mountain Horse, Kentucky Mountain Saddle Horse, Quarter Horse, American Miniature Horse, Morgan, Appaloosa, Missouri Foxtrotter, Virginia Highlander, Paint Horse, Tennessee Walker, Mustang (particularly those found in Oregon, Nevada, and California), Icelandic Horse, Northlands Pony, Australian Pony, Connemara Pony, Shetland Pony, Swedish Warmblood, Finnish Warmblood, Dutch Warmblood, Gypsy Horse, Welsh Pony, Ardennes, Soviet Heavy Draft, and the Byelorussian Harness Horse. It has been determined by DNA analysis that carriers of the Silver gene were also found in the Haflinger breed, but there isn’t a visible color effect because this breed occurs only in the red (chestnut) color. Remember that Silver Dilute horses and dark flaxen chestnuts can look similar.
Silver color displays the following characteristics:
Many silver horses show a characteristic marble pattern on the legs called webbing. This has a “rusty” appearance or looks like whitish, irregular, elongated streaks with sharp boundaries (Photos 45–47).
Ashy or black hair in the mane and tail are found frequently (Photo 48). Silver horses can have yellowish guard hair of a dim, rather dirty shade, but not red or reddish, which would be typical for flaxen chestnuts.
Striped hooves are found in some silver horses, but they are not always present (see Photo 46). They differ from the striped hooves of appaloosa-spotted horses (see p. 55), because the stripes in silver horses are not black, but dark gray, and do not have sharp borders. Often their stripes are wedge-shaped. Striped hooves can be observed in foals, although in the process of the horse maturing, they may disappear.
Pronounced seasonal dapples are observed in some silver horses (silver dapple—see p. 28), appearing in summer and vanishing in winter (Photo 49).
Light eyelashes (white or yellowish), while not present on all silver horses, are a reliable characteristic seen on most (Photo 50).
Silver Bay and Silver Seal Brown
Silver bay is often confused with flaxen chestnut (see p. 39)—for example, in the United States these colors have been recognized as separate entities only since 2002. The silver bay horse has a red or brown color to the trunk and a lighter mane and tail—from dark ashy with separate whitish and yellow locks of hair, to almost completely white (Photo 51). Sometimes the same horse can have a dark and smoky tail paired with an almost white mane, or vice versa. The skin and hooves are pigmented.
The main difference between silver bay and flaxen chestnut are the dark legs, resembling the legs of an ordinary bay horse. In flaxen chestnut animals, the lower part of the legs has a red or whitish color. In the silver bay, the color of the lower part of the legs fluctuates from light to dark brown—to sometimes black. In addition, the ears often have black rims.
A horse with the weakest manifestation of the Silver gene does not differ from an average bay, unless the guard hair is mixed