The Grey Modifier
(or, why TBs can NOT be roan, with one bizarre exception)
| Many grey Thoroughbreds are registered as grey/roan or even just as roan due to confusion that still exists regarding the differences between these two distinct colors. Grey is a gene that modifies the horse's existing coat color (bay, chestnut, etc) by slowly de-pigmenting all of the hairs of the coat as the horse ages. It's a process akin to the greying of human hair. All grey horses are born the color of their base coat, but most will have a few grey hairs around the eyes and muzzle, indicating the presence of the grey gene. As the horse ages, the grey hairs will spread from the face all through the coat. Many grey horses dapple as they age, and eventually end up a very light grey or "white" shade. Below are pictures showing the progression of the greying process on Unbridled's Song. (Photos by ?) |
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| Some greys retain odd patches of color known as "bloody shoulder marks" though the marks can occur on the neck, barrel, and elsewhere as well. The mare Charmander, shown below while racing and a few years later, is a nice example of this. (Photos by ?) |
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| Unlike greys, roan horses remain the same color throughout their lives. Roan acts similarly to agouti and cream in that it only affects the body hairs and not the hairs of the legs, mane, and tail. Thus, roan horses will always have dark heads, legs, manes, and tails, and their bodies will have white hairs mixed in with the coat color no matter what age they are. The roan gene DOES NOT exist in the Thoroughbred breed.* Any Thoroughbred that is registered as roan as actually grey and will lighten with age. The confusion seems to have arisen from bay and chestnut horses that turned grey because they often go through a stage where their coat color is very muddy and looks somewhat similar to roan. |
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| *The Catch A Bird Exception: The only exception to the statement that there are no true, dark-headed roan TBs has cropped up very recently. In 1982, a very unusually marked Thoroughbred was born in Australia named Catch A Bird. He looks like a bay horse with white brindling, the opposite of the dark lines seen on "normal" brindles. Stranger still, as a stallion, Catch A Bird has produced four offspring that appear to be true, dark-headed roans, indicating that Catch A Bird carries a one-time genetic mutation that has produced roan. As far as I know, none of the 4 "roan" foals, Odd Colours (1992 mare), Slip Catch (1993 mare), Goldhill Park (1994 horse), and Red Noble (1996 gelding), have been tested to see if they carry the roan gene, but they certainly exhibit the typical roan phenotype. Please note that these four horses appear to be the only true roan TBs in existence. All other horses regsitered as roan or grey/roan worldwide are actually greys. |
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Pictured at left is Catch A Bird, who looks like a brindle, except with white striping instead of dark striping. With regular brindles, the dark stripes are caused by the sooty hairs in the coat being arranged into lines, rather than being randomly scattered. I can't help but wonder if something similar might be happening to Catch A Bird's coat. I suspect he carries the sabino gene, and perhaps rabicano? Either gene can cause white flecks in the coat that mimic true roan---perhaps Catch A Bird does exhibit one of these patterns and the white hairs have simply been organized into lines like a brindle. That would suggest that there is a relationship between sabino (and/or rabicano) and roan, especially since Catch A Bird has produced roan offspring, but what that relationship is, if there is one, has not yet been determined. |
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Rabicano: More Confusion with Roan
| Pictured below (left) is Colorful Tour winning the 2003 Essex Stakes. He is a chestnut rabicano, a pattern that is often confused with true dark-headed roan. The rabicano gene, however, is entirely seperate from the roan gene, though it does create a pattern of white hairs that is similar to roan. It is usually manifested as a sprinkling of white hairs radiating out from the horses flank. Rabicanos also have a white-topped tail, known as a coon tail or skunk tail. Other notable rabicano TBs are Cox's Ridge, his dam Our Martha, and Carrier Pigeon. There is some thought that rabicano may be tied to the sabino gene. |
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