Roan (color)

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Different meaning: Roan, Norway.

A bay roan horse, sometimes also called a red roan.

Roan is a coat color found in many animals, notably horses, cattle and dogs. It is defined generally as an even mixture of white and pigmented hairs that does not "gray out" or fade as the animal ages.^[1] There are a variety of genetic conditions which produce the colors described as "roan" in various species.

[edit] Roan horses

A blue roan has white hairs intermingled with a black base coat. This horse appears to be a blue roan, though the hints of reddish hair on the muzzle, behind the forearms, and in front of the stifle indicate that its underlying coat may not actually be black

See also: Equine coat color genetics

Any horse with a mixture of white and dark hairs of any color may be called "roan."^[2] Such mixtures, which can appear superficially similar, are caused by a number of separate genetic factors. Many registries do not distinguish between these genetic differences. Identifiable types of roans include true or classic roan, varnish roan, and rabicano, though other currently unknown factors may be responsible for ambiguous "roaning." Gray horses, which undergo progressive silvering, may be confused with roans as well.^[2]

[edit] Classic or true roan

Horses with the classic or true roan pattern may be any base color which is intermingled with unpigmented white hairs on the body. Except for white markings under the control of other genes, the head, mane, tail, and lower legs are dark or unaffected.^[3][2] The overall effect is that of a silver or lightened appearance to the affected part of the coat, which is reflected in the terminology used to describe roans. Black horses that are true roans are often called "blue roan" and likewise, true roan chestnuts are sometimes called "strawberry roan."

Classic or true roan is always present at birth, though it may be hard to see until after the foal coat sheds out. The summer coat may be lighter in the summer, but unlike grays, true roans do not progressively lighten.^[2] While the head of a true roan, barring any white markings, remains solid throughout its life, the first indication of "graying out" is often observed around the eyes and muzzle of foals.

A peculiar characteristic of the roan coat is that after the skin is broken or scraped, the coat grows back without any white hairs. These are called corn marks. Another useful characteristic is that the unaffected color on the legs forms a sharp, inverted "V" above the knee. This is not true of other roan-like coat patterns.^[4]

True roan is caused by a simple dominant gene^[2] that has been assigned to equine chromosome 21 (ECA21) in the KIT sequence.^[3] Other important coat color genes in the equine KIT sequence include tobiano spotting,^[5][6] extension (black), sabino-1 spotting,^[7] and at least four other dominant white-spotting patterns.^[8] These characteristics are part of equine linkage group II (LGII).^[9]

A study published in 1979 examined percentages of roan foals produced by roan parents found fewer than expected for a simple dominant trait. At the time, lethality of genetic conditions was based primarily on statistics, as modern methods of DNA testing and mapping had not yet been developed. ^[10] Neither finding stillborn or short-lived foals from these roan parents, the researchers concluded that in the homozygous condition the roan gene was lethal to the embryo or fetus. Contemporary studies were beginning to identify conditions such as "dominant white" and "lethal white," and so roan was believed to follow a similar pattern. Genetic science in the 1970s could not provide a clear answer. "Lethal roan" has since been discredited by the identification of homozygous roans^[11] and the work of the late Dr. Ann T. Bowling, who found no evidence to suggest that homozygous roan was lethal.^[12]

This bay roan exhibits the inverted "V" of color above the knees, also has white markings on its lower legs

The dominant inheritance of this trait means that two non-roan horses cannot produce a roan, although roan may occasionally be masked by gray or extensive white markings. True or classic roan is most common in European draft breeds like the Brabant, Ardennes, Trait Du Nord, Italian Heavy Draft and Rhenish-German Cold-Blood though it is found regularly in Quarter Horses, Paint Horses, Dales Ponies, Welsh Ponies, and Miniature horses and very rarely in Trakehners and American Saddlebreds. True or classic roan has not been satisfactorily identified in Arabians or Thoroughbreds.^[13]

Descriptions of roan coats warrants its own terminology:

• Red Roan or Strawberry Roan describes true or classic roan on a chestnut base coat. The mane and tail remain red or have only a few white hairs, while the body ranges from nearly chestnut to pinkish.
• Bay Roan is true roan on a bay coat. The particular shade depends on the underlying shade of bay, but the mane, tail, and lower legs are black and the reddish body is intermingled with white hairs. The head is usually red. Formerly, bay roans were lumped together with red roans.
• Blue Roan is true roan on a black coat. The mane, tail, head and legs remain black while the body takes on a grayish or bluish appearance. Blue roans are sometimes mistaken for grays or grullos. However, Grays fade with age, while roans do not, and grullos are blue duns and possess dun markings but not intermingled white hairs.

Any coat color may be affected by roaning. Few combinations have the same unique terminology applied to the common roan colors, although palomino roans are sometimes called honey roans.

[edit] Varnish Roan

Main articles: Appaloosa#Genetics and Varnish roan

A varnish roan Appaloosa, showing white sclera, mottled skin, dark head, and classic head pattern

The varnish roan is not a true roan, it is actually one of the leopard complex coat patterns associated with Appaloosa, Knabstrupper, [[Noriker horseand related breeds. Varnish roans are not true roans and can be distinguished from true roans by the following:

• Appaloosa/leopard characteristics. Varnish roans, like all horses with the Lp gene, have mottled skin, striped hooves, and white sclera.
• Varnish roans change color seasonally, often becoming less spotted as they age, and often having their coats become lighter when a winter coat grows in, though they do not progressively lighten in the manner of a gray horse.
• Varnish roans do not retain solid heads that true roans possess.^{[citation needed]}
• Bony areas retain their pigment longer. These areas include the bridge of the nose and cheekbones, ears, points of shoulder and stifle, as well as the legs.
• Appaloosa/leopard characteristic parentage.

Varnish roan is thought to occur due a single, simple dominant gene on equine chromosome 1 (ECA1).^[14] It also appears that specific white patterning genes produce the assorted blanket, leopard, and snowflake coat patterns.^[15] Without these white patterning factors, horses with one or two copies of the dominant Lp gene are "varnish roans." Varnish roans can be considered to have many, many very small leopard spots that reflect the mottling of the underlying skin.^{[citation needed]}

A horse may be varnish roan as well as true roan and gray, but such combinations are extremely uncommon. The breeding of grays is discouraged by the Appaloosa Horse Club and not allowed by Knabstrupper breed registry.

[edit] Rabicano

Main article: Rabicano

An extensively expressed rabicano Arabian horse

Rabicano is a white pattern that falls into the category of roaning or scattered white hairs, the genetics of which are not yet fully understood.^[2] Sometimes called ticking, rabicano is common even in breeds that do not have true or classic roan, including Arabians and Thoroughbreds. This pattern usually takes the form of scattered white hairs around the junction of the stifle and flank, and peculiar rings of white hairs near the base of the tail. This trait is called a coon tail or skunk tail.^[12] Extensively-marked rabicanos sometimes exhibit striations in their pattern on the ribs, giving them a striped appearance.^[13] While rabicano itself does not produce white markings on the face and legs, it is often associated with any of the numerous sabino patterns, many of which have been mapped to the KIT gene.^{[citation needed]} Other color patterns mapped to KIT include extension, tobiano, and true roan.^[3][6][9] This may explain the close association between rabicano and sabino, which are often observed in the same horse.^{[citation needed]}

Scattered white hairs on this red mare's flanks indicate rabicano. (click to enlarge)

Rabicanos are not true roans and can be distinguished from true roans by the following:

• Roaning on rabicanos is centralized at the junction of the stifle and the flank; true roan is evenly distributed over the whole body except the points.
• Rabicanos usually have skunk tails or rings of white hairs in the tail, while true roans do not.
• Rabicano roaning often spreads, while true roans usually become darker.
• Rabicanos do not develop corn when their skin is damaged.

Rabicano may occur on any base color and may occur in conjunction with any other white pattern, including true roan or gray.

[edit] Sabino

Sabino coloring may have roaning patterns on the edges of white markings, as in the case of this horse which has both overo and sabino spotting patterns, but these intermingled hairs are not indicative of a true roan

Main article: Sabino horse

Some forms of sabino, which is a pinto pattern, have roaning along the edges of other white spots or markings This pattern is often, though not always, associated with a broad blaze on the face, leg markings that are especially high on the hindlegs, and belly spots. The edges of the white markings are often ragged, irregular and frequently include intermingled scatterings of white hairs that resemble roan. Though at least one form of Sabino is also genetically linked to the KIT locus, it is not true roan, there are different genetics involved. True or classic roan is not associated with broad white markings of any kind.

[edit] Other types of roaning

A roan horse horse may not fit into any of the traditional categories as there is much still to be learned about the genetics of roan. For example, in studies of mice, of the more than 180 identified genotypes that produce white patterning in laboratory mice, no fewer than four produce roaning or flecking.^[16] The existence of other types of roaning conditions not covered by those mentioned here is possible and likely.^[2]

[edit] Roan dogs

Australian Cattle dog

The genetics behind roan dogs are still unclear, and at present candidate genes have been ruled out.^[17] There remains a great deal of ambiguity in terminology regarding mottled dogs, which are called roan, ticked, mottled and belton depending on the context. The roan or ticked color is described in many breeds of gundogs such as English Cocker Spaniels, American Cocker Spaniels, Field Spaniels and Brittanys, German Shorthaired Pointers, Spinoni Italiani, Lagotto Romagnolos and English Setters, as well as Border Collies and many other breeds.

In dogs, roan manifests itself only in unpigmented areas, the presence and shape of which are determined by other genes.^[18] This is in stark contrast to true roan horses and roan cattle, which are roan only in pigmented regions of their coat and may have white markings. Instead, dogs with roaning or ticking are born with clear, open white markings which begin to fill in with flecking in the subsequent weeks and continue to darken with age.^[19] Most breed standards use the terms "ticked" and "roan" interchangably, with the former referring to clearly-defined flecks on a white background and the latter to flecks so closely-spaced that the mixture appears even.^[20] The terminology that relates the underlying coat color with the roan modifier is often breed-specific, but most standards call a black dog with roaning blue. In breeds that are characterized by roaning and ticking such as the the Large Munsterlander, clear white-marked individuals may be called plated.^[18] The term belton is reserved for English Setters.

In 1957, Little suggested that roan and ticking were controlled separately, and postulated that roan may have been homologous to "silvered" coat in mice.^[20] This condition in mice is actually homologous to merle, which might be described by some as "roan."^[21] In 2007, the gene responsible for roan cattle (KITLG) was refuted as a possible cause of roan in dogs. Neither roan nor ticking, if they are independently-caused, appear to be recessive.^[17]

[edit] Roan cattle

Red roan Shorthorn heifer

Breeds of cattle known for roans are the Belgian Blue and Shorthorn. Among the former, coat color may be solid black, solid white, or blue roan; the latter may be solid red, solid white, or red roan. Belgian Blues also typically exhibit spotting patterns,^[22] which are genetically separate from roan. As a result, most roan cows exhibit blotches of clearly colored and clearly white hair, with roan patches.^[23] Some "cryptic" roan cattle appear solid, but upon close inspection reveal a small roan patch.^[24] Roan cattle cannot "breed true" but breeding white cattle to a solid mate will always yield a roan calf. The white color typical of Charolais and White Park breeds is not related to roan.^[24]

Roan in Shorthorns and Belgian Blues is controlled by the mast cell growth factor (MGF) gene, also called the steel locus, on bovine chromosome 5^[25]. Part of the KIT ligand, this region is involved in many cell differentiation processes. Mast cell growth factor promotes pigment production by pigment cells ^[26], and without it, skin and hair cells lack pigment. With two functional MGF genes ([homozygous] dominant), cattle are fully-pigmented; without any functional MGF genes ([homozygous] [recessive], they are white. MGF-controlled roan occurs when cattle possess one functional and one non-functional MGF gene ([heterozygous]), resulting in a roughly even mixture of white regions and colored regions.^[24]

The reproductive condition "White Heifer Disease," associated with the MGF gene, is characterized by homozygous MGF-white heifers with incomplete reproductive tracts.^[27]

[edit] Roan Guinea Pigs

The roan coloration of Guinea pigs is linked to microphthalmia. The allele that controls roaning in guinea pigs is incompletely dominant: an animal with one copy of the allele will have varying amounts of white hair scattered through its coat, particularly on the back and sides. This is not to be confused with the 'Magpie' variety, which is a brindled guinea pig lacking red pigment due to the "chinchilla" allele also responsible for self white and silver agouti coloration.

About 25% of guinea pigs born to a mating of two roans are completely white, with a constellation of deformities called lethal white syndrome, although it has no relation to Overo Lethal White Syndrome in horses or double merle syndrome in dogs. These symptoms include:

• Partial or complete blindness
• Partial or complete deafness
• Microphthalmia or anophthalmia
• Unpigmented eyes
• Missing or deformed incisors
• Deformed molars
• Elongated tooth roots
• Malabsorption in the small intestine, due in some cases to lack of intestinal villi
• Increased susceptibility to illness

It is worth noting that, unlike anophthalmic hamsters, lethal white guinea pigs are not sterile. Females may be unable to deliver live young.

Lethal white guinea pigs have a decreased lifespan in general, although individuals have reportedly lived to 6 or 7 years. Many die shortly after birth or at weaning age. With hand-feeding and regular dental care, lethals can live 2-3 years.

[edit] References

• "Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008

[edit] See also

• Equine coat color genetics
• Equine coat color

[edit] External links

Horses

• Photo of blue roan
• Photo of chestnut roan
• Photo of smoky black roan (black + 1 creme gene + roan)
• Photo of silver dapple roan
• Horse Coat Color Genetics (Including roan definition, photos, and genetic formulas)

Dogs

• Photos of roan English Cockers
• Photos of roan Australian Cattle dogs

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