Category: Horses


This time I’m discussing a pair of markings that may or may not be genetic: manchado and brindle. Sorry, I don’t have any photos, but scroll down the White Horse page and look at Figure 8.120 in Sponenberg.

Manchado is in the pinto group if it is genetic, but it has hardly been investigated at all. Sponenberg says it is primarily found in Argentina, but it is found there in several breeds. This is taken by some as indicating an environmental cause, and by others as indicating that Argentineans pay more attention to horse color than do people in other parts of the world.

There is no question that manchado is different from other spotting genes. At first glance, it is a combination of pinto and leopard (Appaloosa) traits, but manchado horses do not have known leopard or pinto genes. The minimal expression is white on the top of the neck, giving a partially white mane, like tobiano. The head and legs normally remain dark. The white areas are crisp-edged, but these white areas normally have round or oval colored spots within them.

There are a few photos on the web, most notably one showing a Throughbred stallion and an Arabian mare, both breeds which are rarely spotted. Sponenberg shows a photo of a Welsh Pony with the Manchado pattern, but does not state whether is particular individual was from Argentina.

Brindle is a little better understood, but not by much. There are three types of bindles, one involving black stripes, one involving white stripes, and one in which the horse is actually a chimera. In the first two cases, much more common genetic mechanisms appear to be necessary.

For black stripes, the horse must have black interspersed hairs, a condition called sooty by geneticists. In most horses, the interspersed hairs are uniformly mixed into the coat or more numerous toward the back of the horse. In a few horses, the black hairs are organized into vertical stripes.

If white hairs are present, as in roans, they may also occasionally be organized into vertical stripes. This is also referred to as brindle, though it is not known whether this type of brindle has any relationship to the type with black stripes. The rabicano  pattern is an example of this type of brindling.

Finally, it is possible that two fertilized eggs are merged in early gestation. The chimera that results actually has tissues with two different DNA sets, and these tend to be arranged in vertical stripes. A brindle of this type could actually combine any two colors found in horses.

A website from White Horse Productions has excellent photos of these and other rare modifiers in horses. Scroll through the entire page.

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I thought at first I’d post her first view of Rakal by a young mother from Horizon, but I’ve been blogging that for Six Sentence Sunday for six months now. Instead, I picked another piece from War’s End (in the editing stage.) Mik is from Horizon, and is getting his first good look at Central, very early in spring. Kevi was the name Roi used on Horizon. I hope it’s not too long.

Click on the logo to find the other participants in the World Building Blogfest.

World Building logo The map looked like any other satellite map, except for the light point that marked Mik’s position, and the way the map rotated in its frame as he moved and changed scale when he ran his finger up or down the side. Handy, actually, ahead was always up on the map. The scale had given him a little problem at first, until Kevi had identified a bar that grew and shrank with the map as showing the distance a horse at a traveling trot could be expected to cover in half an hour. A longer bar was an eight-hour journey, and when he zoomed out to include the whole K’Roi reservation, only that longer bar was clearly visible, and surprisingly small. Kevi hadn’t exaggerated at all on size, Mik decided.

The yellow cross the light was approaching, out behind the stables, was the symbol for a gate. “Let Timi control it going out,” Kevi had said, “and get hold of me with the com if you want to use one.” Too bad Kevi hadn’t told Timi that a little more clearly. What was it with kids that they always assumed they knew more than adults did?

“This one goes to about twenty different points around the Reserve,” Timi was saying as they approached a misty area between two trees. “You use it by visualizing where you want to go, or by thinking a code symbol, or even the name of your destination.”

“Kevi—ah, Roi—said just to follow you and let you worry about setting it,” Mik said, patting Ripple’s neck. Coin was here—Roi had teleported him back from Horizon yesterday, when he’d gone to inform the delegation that Madame Irela was missing, and he’d taken along another telepath to go on the ship that was to transport the rest of the delegation. That ship wouldn’t go missing, or if it did, Kevi would be able to contact the other telepath. If Mik turned his head, he could see his stallion investigating his paddock. But the horse didn’t look as sure-footed as usual, and Mik was inclined to trust Kevi’s advice that it would take the horse a few fivedays to get used to the stronger gravity of Central.

Timi was riding into the mist ahead of him, and Mik reined Ripple after him. “We’re going up, so your ears’ll pop,” Timi called back, and then the mist closed around them. Mik’s ears did pop as the mist briefly hid everything around them. When the mist cleared, Ripple was on a trail through open forest quite unlike anything Mik had seen around the stable. This was hill country, he saw, and he took a deep breath of the chilly air. Just as well Kevi had insisted he dress warmly.

Terry and Kevi had both said that the Horizon ecosystem was incomplete, with many species deliberately excluded. Looking around him, Mik was astounded at the diversity of plant life. More kinds of trees were visible from this one spot on the trail than he knew on all Horizon, and the lower-growing plants were equally variable. Food plants? He thought he recognized a few berry bushes as Ripple trotted by, but it was the wrong season for berries. About half of the trees had shed their leaves, and a good part of the path was sunlit. He looked up, and saw prickly objects on the branches of one otherwise bare tree. “Are those edible?” he asked Timi.

The young man reined in his horse and looked up. “I think Tod said once they were,” he replied doubtfully, “but I don’t get my food that way. There’s plenty of reliable food in the shelter cabins.”

Well, Mik already knew that Timi, though from Horizon, was town-bred. He memorized the look of the tree, noted that it grew on a sunny slope well above a creek they were descending toward, and put a couple of the spiny things from the ground under it into his saddlebags. He might not need food sources, but Tod would. He glanced back at the map, now with a little better feel for what it showed.

Kevi was positive that Tod was in the K’Roi reserve, and reasonably certain that the boy—no, young man now, Mik reminded himself—was somewhere in the foothills of the mountain range occasionally visible to Mik’s left. They had exited the gate near the northern boundary of the reserve, and Mik’s plan was to follow the trail that wound among the foothills to the southern boundary, leaving clear signs of his passage. Thinking of which ….

WoodlandMik halted Ripple and dismounted just before the creek, handing her reins to Timi as he searched out several sticks and pebbles. He arranged these to the side of the trail, well above waterline, then took a bit of bright blue ribbon from a bundle in his saddlebag and tied it to a branch over his arrangement. Timi watched in fascination. “What are you doing?” he finally asked.

“Leaving a message for Tod,” Mik replied as he swung back up onto Ripple. When the mare was shod for the trip he’d made certain her shoes were rimmed, to leave clear prints, and he was fairly sure Tod would spot those prints. At least, he would if he was anywhere near the trail, and if there was no hard rain to wash out the prints—a shaky assumption at this season, Kevi had told him. But the cloth flags, near sites where the hoof prints should be clear, would catch Tod’s eye; and the arrangement of stones and twigs carried the message that Mik wanted a meeting. If Tod remembered what Mik had tried to teach him, eight years ago, he’d understand the message.

“No telling where he is,” Mik continued, “but I suspect he’ll be keeping an eye on the main trail. He’ll check for hoof prints where the ground is most likely to hold them—near stream crossings—and that’s where I’ll leave sign. I won’t get a fast response, but by the time I reach the southern boundary he should have found at least one of my markers. Then I’ll head back north—on Coin by then, I hope—and watch for any reply. Walk them up the slope, Timi.”

“Tod always had us keep a steady trot.”

“That’s for conditioning. I want to cover the maximum ground with the minimum wear on the horse. That means walk uphill and down, move out at a lope or a working trot on level ground with good footing, and change diagonals regularly at the trot. You’ve been on the left diagonal ever since we started.”

“Now you sound like Tod,” Timi grumbled. “Is he really as good as he thinks he is?”

“He has a real gift for understanding horses, even by nomad standards,” Mik replied. That was based not only on his memories of Tod, but also on his observations yesterday of the horses and riders his nephew had trained. Kevi might be worried about the clan’s accepting Tod; Mik was not. A few of Domik’s cronies might think Tod was stealing Dom’s place, but that would be short-lived. Mik’s concern was mostly whether Tod had the judgment to make good, reasoned decisions, to stand by those decisions, and—hardest of all—to admit error if changed circumstances proved him wrong. All without losing the confidence of the clan.

Mik shook his head violently, making Ripple flick her ears back in question. He didn’t know if he could live up to that, and the best he could do with Tod would be to determine whether his nephew promised to be an adequate leader. And if Kevi was right, talk him into taking on the burden of leadership.

Eyes and map alike showed a level, gently curving stretch ahead, and Mik automatically cued Ripple into an easy lope. The mare tossed her head eagerly, bringing a burst of sound from the bells on her bridle. Mik looked from side to side as he rode, alert to the woodland around him. A patch of mixed cream and rust caught his attention, and he signaled Ripple for a halt. “What,” he demanded, “is that?”

Timi came up beside him, squinting in the direction Mik was looking. “A foojah,” he replied matter-of-factly. “They eat leaves and shoots—that long neck helps them reach way up. They’re pretty common. It’s a R’il’nian species. Not dangerous, unless you corner one. They’re prey for wolves, bears and akedas.”

“Oh,” Mik said weakly. The animals—there were three, he saw now—were about the height of a horse at the shoulder, but with longer necks. They were creamy underneath and a darker, rust color along the back, and one had a black crest of stiff hairs or feathers atop its head. Wolves, he knew, were the wild ancestors of dogs, but he could not imagine a dog threatening something that size. And the other two species Timi had mentioned …. “How big are the predators?” he asked. “Kevi showed me tri-dees, but there was nothing for scale.”

“Wolves are smaller than a foojah but a lot larger than the pocket herders, and they hunt in packs. A good-sized grizzly would outweigh a foojah. Akedas don’t weigh that much—they’re from R’il’n, too, and closer to birds than mammals—but their heads are higher than a foojah’s back. We don’t have pumas locally—the akedas take their place in the local ecology, Roi says. The warnoffs work against all of them, and there’s a gadget that works the same way that keeps them out of the settled lands and away from the cabins.”

“Warnoffs,” Mik said weakly. Kevi had explained the gadgets to him, but he hadn’t paid too much attention. Seeing the size of the animals the predators preyed on had him wanting more information. “How do they work, again?”

“They send out two messages. One is ‘I’m harmless.’ That lets you observe the animals, but it also keeps them from attacking you as a threat. The second is ‘I’m not edible and I’ll make you sick if you try to eat me.’ That keeps the predators from viewing you as prey. Course neither one is much protection if you startle an animal from too close, so we use the bridle bells to let them know we’re coming.”

Mik nodded. He’d thought of removing the bridle bells so he could hear the sounds of the forest—but not if they were a safety precaution. Timi did know some things better than he did, he reminded himself. He nudged Ripple back into a trot and looked down at the map. “That’s a shelter cabin up ahead, isn’t it?”

“Yes. We’re making good time—ought to be there in an hour. Want to stop there for lunch? They’re all pretty similar, so I can show you how they’re set up.”

He may have his height, Mik reminded himself, but he still has a lot of filling out to do—hardly surprising he thinks a lot about food. Good thing his horse is a weight carrier, though. Most of ours would be too light.

Terror Bird

This is the only public domain image I could find of a South American terror bird. The akeda would have some similarities but be much brighter in color.

Mik hadn’t quit worrying about Coralie, but the only thing he could do for her was try to find Tod and hope that Kevi could do better than he thought he could with contacting Coralie through Tod. Meanwhile, he might as well learn all that he could about Central. He kept looking from side to side as he rode, and saw two more groups of the foojahs, as well as several smaller animals Timi said were deer. It was close to an hour before he saw something even stranger, and much more frightening. “Is that an akeda?” he asked, but the really didn’t see what else it could be.

It was tall—he doubted he could see over its back if he were on the ground—with a neck that put its head above the height of a horse’s. Half or more of that head was beak, a powerful, crushing beak. Strong legs appeared to be scaly skin over bone, while the body of the creature was covered with dull gold and green feathers—at least, he thought they were feathers—with a fanlike green crest on the head.

“They get a lot brighter during mating season,” Timi said from behind him, “and the males get a sort of train of feathers. They’re really gorgeous then. Roi says they have a lot in common with the terror birds that were on Earth twenty thousand years ago. There’s the cabin.”

Splashed white is another spotting gene in horses. It resembles tobiano in that the pattern is usually crisp-edged, and there is no tendency for the kind of uneven roaning often seen in sabino. Splashed white is more common in Europe than in North America, but is becoming common in Paints.

The best description of splashed white is that the horse looks as if it had been dipped feet-first in white paint with its head lowered. Minimal white markings may not be recognized as due to a spotting gene. The next stage includes a blaze that widens toward the muzzle and may extend up the sides of the head, white extending above the knees and hocks, and possibly a belly spot. With stronger grades of spotting the entire head is often white, as well as the entire underbody, and eventually only the ears may retain pigment. Eyes are usually blue or have blue chips. Splashed white can be confused with very crisp sabino markings without roaning, but sabino-1, at least, can be identified through genetic testing.

I am sorry I have no photographs of this pattern, but it is rare in North America. Even Sponenberg’s photos are of Icelandic horses. Splashed white can be very difficult to tell from a crisply marked sabino without roaning. The amount of head white would be unusual for a tobiano. In general tobiano markings look as if white paint was dripped over the horse from the top, while the white in splashed white gives more the appearance of coming up from the bottom. The pattern occurs and is being selected for in Paints, and is known in Icelandic horses,  Welsh Ponies, and Finnish Draft Horses. It also is known in the Appaloosa.

Splashed white appears to be associated with deafness in horses, though many splashed whites have normal hearing.

Splashed white is believed to be due to a dominant or incompletely dominant gene, though the wide range of patterns produced by this gene makes genetic studies difficult. There is evidence of at least one white horse being homozygous for splashed white. At the present time, a DNA test for this gene is not available. There is conflicting evidence as to whether this pattern is associated in any way with the KIT locus.

Chestnut Frame horse

Chestnut paint. This particular horse appears to have the frame allele rather than sabino, judging from the face and lower legs, in spite of the ragged appearance of the spots.

Frame is another type of spotting gene in horses, formerly lumped into overo and sometimes called frame overo. It has nothing to do with the KIT locus, unlike tobiano and sabino-1.

Frame involves patterns of white which do not usually include roaning, though frame may occur in conjunction with other genes that cause roaning. In frame, the white areas tend to be arranged horizontally on the sides of the horse, and almost never cross the back. Frame is also almost the only pinto pattern in which the legs remain pigmented, though normal leg markings may occur.

Like all spotted horses, frame horses may vary from mostly colored to predominantly white. A frame horse will almost always have a wide blaze or bald face, and an apparently unspotted horse with a bald face but no white leg markings is likely to be a minimally marked frame. As the white expands the head may become mostly white and the white areas on the sides may expand to cover most of the horse, with the spine and legs being the last areas to lose color.

Black and white frame horse

Another Frame. Note minimal leg markings with wide blaze and white spots on sides.

Frame is due to a single allele, frame (Fr), at a locus called endothelin receptor b (EDNRB) on equine chromosome 17. The locus has two known alleles, frame (FrFr) and wild-type (Fr+). Frame horses, some of which are so minimally marked as to look solid, have one frame and one wild-type allele.

Breeding two frame horses together may produce lethal white foals, with two frame alleles. Such foals are born white, and the part of their nervous systems that controls the lower intestinal tract does not develop properly. They normally die within 72 hours of birth, though most are euthanized as soon as they are recognized. Most breeders avoid mating two frame horses together in order to avoid the production of such foals.

The frame allele can be tested for. Such testing has demonstrated that some genetically frame horses appear to be solid colored. Whether this is due to a suppressor gene or genes or is simply the extreme end of random variation of amount of white is unknown.

(If you’re here because you like horses, my story, Horse Power, is free today on Kindle. Click on the cover in the sidebar.)

Sabino Spotting in Horses

“Chico”, owned by Charlotte Rowe

For many years two types of “pinto” spotting were recognized—tobiano and overo. Overo has now been broken into a number of distinct spotting genes—frame, splash, sabino-1, other sabinos, polygenic sabino, some types of dominant white, and manchado. Sabino now seems to be as much a grab-bag of genetically different types of white markings as overo once was. Here I will concentrate on Sabino-1, while noting that several other genetic types of sabinos and dominant whites seem to be associated with mutations at nearly the same locus.

Sabino jumper

Sabino with near minimum markings.

The sabino pattern has a wide variety of expressions, and some can be easily confused with other types of spotting, or even with roan. Sabinos not infrequently have areas of roaning as well as white spots, or flecks of color within the white areas. Almost all have white feet and facial markings, and the minimally marked ones can sometimes be detected by narrow extensions of the white up a leg or down the throat. The horse in the photograph to the right, for instance, has extensions of the high stockings in points up the legs as well as small white belly spots.

Sabino head

Sabino head, showing white underside.

In contrast, tobianos tend to have white legs but relatively plain faces, while frame horses have heavily marked faces with generally dark legs. It is unlikely that a sabino would have a completely plain head or completely dark legs, but sabino can certainly mimic any of the other pinto patterns combined with normal face and leg markings.

The sabino-1 allele is due to a single base-pair change in intron 6 of the KIT locus on equine chromosome 3. This means it is very tightly linked with tobiano and roan, both of which are also associated with the KIT locus. There are actually a number of mutations at the KIT locus that can produce sabino-like patterns.

Sabino

Note the ragged, flecked appearance of the white.

Sabino-1 is incompletely dominant to the wild-type allele. This means that a horse with one sabino-1 allele and one wild-type allele will be a typical sabino. A horse with two sabino-1 alleles may be mostly white, often with a pattern approximating the “War bonnet” pattern—color in a head bonnet, chest patch, flanks and tail base. This pattern, however, can also be produced by combining the tobiano and frame genes. Sabinos sometimes come from two parents that appear to be non-spotted, but as with tobianos, one parent is generally a minimally marked sabino.

Some of the other KIT-related sabino alleles may be lethal when the foal inherits them from both parents, but this is still being investigated. There is also the problem that it may not be possible to determine visually whether a sabino may have more than one spotting gene.

The sabino-1 allele is well known and a genetic test is available.

Well, I did it.

HORSE POWER Working A 2aI just clicked the “save and publish” button on Amazon Direct for my short story, “Horse Power.” It should be available for purchase at $.99 by this evening — I’ll update and link the cover to Amazon when it goes live. Update 10 pm: it’s live at Amazon.

I firmly believe that e-books should be less expensive than mass-market paperbacks, especially for new authors. I’ve been fighting with iUniverse on this (they want to price e-books at $9.99) and finally got Homecoming and Tourist Trap down to $4.99 each in e-book form at their site. The e-books should be even less at Amazon and Barnes and Noble, but it will probably take a while. (If they don’t show a lower price by the end of the month, complain to them.) Meanwhile, I have a story between the end of Tourist Trap and the start of the trilogy I’m editing now, so why not get it out, and learn to use Amazon direct at the same time? Thus “Horse Power.”

If you’ve read Tourist Trap, you may have wondered what happened to Timi and Amber after the end of that book, and this is their story, 22 years later. To quote from the blurb I’ve put up, “Rumors have reached the Inner Council of the Jarnian Confederation that the Horizon Company is illegally exploiting the colonists. Roi has been sent to find out what’s happening, and he asks his old friends, colonists Timi and Amber, for help. But the Company’s behavior is legal, if immoral. Can the three find a solution to the problem?”

The trilogy will be about a future war between the Confederation and Horizon, and the events in this story will be pivotal to that future, innocent as they seem at the time.

The cover, which I’m showing here for the first time (Ta-da! Cover reveal!) was done by Tomomi.ink. Like it? I do!

P.S: I’d love reviews on any of my books — especially if you like them!

Tobiano horseTobiano was the first type of white body spotting in horses recognized as being genetically distinct. Like other white markings, it varies widely in extent, with tobiano horses ranging from white with a colored head to normally colored with white hooves and lower legs, and perhaps a white area in the mane or tail. A few tobianos have blue eyes which are apparently produced by the tobiano gene.

The tobiano pattern has relatively crisp-edged white spots that cross the topline. The arrangement tends to be vertical, though not to the extent of a striped pattern. The head normally remains dark, though the white markings seen on non-spotted horses may be present. At times the dark skin extends under the edges of the white patches, giving a “halo” effect. Portions of the mane and tail growing from white areas are normally white, and in fact this may be the only obvious expression of tobiano in a minimally marked horse.

The pattern is due to a dominant allele, tobiano, at the tobiano locus, To. This locus is near but not at the KIT locus on chromosome 3, and a marker test is available. A horse with two copies of the tobiano allele is perfectly viable and not usually whiter than one with one tobiano and one wild-type allele. It is, however, more likely to show “paw prints” or “bear paws”–roan or spotted areas within the white patches.

Tobiano can occur on any base color: intense, dilute, or with interspersed white hairs. It does occasionally have an odd effect in the presence of one copy of the cream gene. The colored part of the coat “breaks up” into patches of dilute and non-dilute hair. This variation of the pattern is called calico. Calico is thought to be due to a dominant gene at a third locus which can only be detected if both tobiano and cream alleles are present. Theoretically, smoky calico should occur with areas of smoky, black, and white, but I cannot find any reference to this color in Sponenberg.

Although tobiano is dominant, tobiano foals are now and then produced by parents that appear non-spotted. On close examination one of these parents is generally a minimally marked tobiano, with extensive leg white and vary little face white.

The tobiano in the video is a good example of the pattern. Note the way the white markings on the neck are carried into the mane, and the way the white patches cross the topline.

Any color horse, full color, dilute, or with intermixed white hairs, can have white body markings. These have long been recognized as falling into two categories: leopard (Appaloosa in North America) and pinto (or paint, piebald, skewbald, or parti-colored.) I’ll leave the leopard complex for later, beyond noting that the horses in Tourist Trap have leopard complex markings. For today, I’ll just give a brief overview of the paint/pinto nomenclature.

Tobiano

Tobiano

In British usage, a piebald was a black and white horse, and a skewbald was red and white. This distinction is rarely made today. Rather, the color of the horse—bay, black, palomino, red dun roan silver, or whatever—is followed by the pattern of marking. And there are a lot more patterns recognized today, often due to quite distinct genes, than was the case when I first became interested in horse genetics!

Paint and pinto are in fact synonyms when they are used as descriptive terms, though they have separate breed registries. In North America the word pinto may be more common in the east and the word paint in the west, but either may include any of the patterns of white body spotting.

Black & White Frame

Probably frame, based on the wide blaze and generally dark legs.

The first breakdown came when tobiano was recognized as being genetically distinct from overo. Then it turned out that there were several genetically distinct patterns being lumped together as overo—just about everything that wasn’t tobiano, in fact. The latest version of Sponenberg gives no less than seven patterns of white body markings, not including the leopard complex or the dark-eyed solid white of the American Albino. I’ll give a very short summary of the seven here, and cover specific patterns and what is known of their genes in later posts.

Tobiano is a relatively clean, crisp spotting with white legs but generally dark heads. White markings tend to be vertical and generally cross the back in all but minimally marked animals.

The frame pattern was once considered typical overo. It is horizontal, tends to affect the head first and the legs last, and white rarely crosses the spine. Frame to frame breeding can produce white foals that die shortly after birth.

Sabino

Sabino, showing both the ragged outlines and the roaning typical of this pattern.

Sabino-1 horses normally have both face and leg markings, and often have roaned areas as well. They are usually not as crisply marked as tobianos, but they vary widely and confusion with almost any of the other patterns is possible. Roaning often occurs and is an expected part of the pattern.

Splashed white gives the appearance of the horse being splashed with white paint from below. The legs are normally white, and so is the belly area. In addition, white is normally present on the head, often to such an extent that the head is entirely white.

Polygenetic sabino and the form of dominant white that sometimes produces colored areas are not well characterized genetically. but are apparently distinct from the other forms of white spotting.

The final pattern, which is very rare, is called manchado, and has been seen in several breeds in Argentina. In this pattern, white first appears along the top line, and can produce a white mane on an otherwise colored horse. The head and legs tend to stay dark as the white areas grow larger, and there are often dark spots in the white, giving a superficial similarity to some leopard patterns.

All of these patterns vary widely in the amount of white, and all have pink skin under the white portions of the coat. I’ll take them one at a time in later posts.

Rabicano under saddle

Rabicano under saddle

This week will be a bit of a catch-all, covering a variety of patterns of white hairs that are neither grey, classic roan, face and leg markings, or associated with white spotting. (Varnish roan, for instance, is a leopard gene pattern, and sabino and dominant white may also produce roaning as part of the pattern.) The genetics of none are well understood. Following Sponenberg, I will list and describe them here. Sorry for the lack of photos, but I haven’t even seen all of these patterns myself.

The first, frosty, may be a variant of classic roan, as it is found in the same breeds. In this pattern, the roaning is most pronounced over bony areas such as the hips, and roaning may affect the mane, tail and head as well as the body. “Squaw manes” and “squaw tails” with white hair mixed in often indicate the frosty pattern. Although there is little doubt that the pattern is genetic, it is not well understood.

“Roaned” is used to refer to horses with a scattering of white hairs not due to the roan or grey genes. It is not always possible to distinguish them from minimal classic roans, but they do occur in breeds where roan does not occur.

Rabicano tail

Rabicano horse, showing the white at the tail base.

White ticking is a much more specific pattern, involving the base of the tail and the flank. It is not progressive and may occur on any base color. Tails with the base white are sometimes referred to as “skunk tails” or “coon tails.” In Spanish the pattern is called rabicano. This pattern is one of the few “roan” patterns to occur in Arabians. Inheritance is thought to be dominant.

Birdcatcher spots are small white spots scattered over a horse’s body. They are named for a Thoroughbred horse, Irish Birdcatcher, who had such spots. They run in families so probably are genetic, but no studies have been carried out.

Rabicano horse

Rabicano, showing how white hairs are arranged in stripes on the sides.

White striping is very rare in horses. The vertical white stripes may be a form of roan, as seen on the rabicano photos. Or it may simply be an accident of gestation. One striped Thoroughbred in Australia, Catch a Bird, is himself striped but is producing as a classic roan.

Finally, minor white markings may occur as a result of scarring. These are most common with freeze branding or saddle sores, but one pattern, called white lacing, is commonly due to a skin problem called reticulated leuktricia. Most often the growth of white hair in a net-like pattern over the hips and back is preceded by the formation of crusts in the skin, but not always. Both genetic and environmental causes seem to be involved. If you have an Amazon account, you may be able to see Sponenberg’s photos here.

Next week I’ll start discussing the patterns usually called paint or pinto.

This information is an update of an earlier post.

The Roan Gene in Horses

Roan, like grey, is a pattern gene which sprinkles white hair over an otherwise normally pigmented animal. However, the pattern of white hair, the progression with age and the response to scarring are quite different from grey.

It should be pointed out that horsemen use the word “roan” quite loosely. In Thoroughbreds, for instance, it is used as a synonym for grey, particularly rose grey. There are several forms of roan covered by this loose usage, but the one discussed here is classic roan, which is due to the dominant roan gene. Frosty roan, varnish roan, roaned, rabicano and the roaning caused by some white spotting patterns will be discussed separately.

Roan on blackIn classic roan the head, legs, mane and tail remain fully pigmented but there is an admixture of white hairs on the body of the horse. Foals are born roan or shed their foal coat to roan, and beyond that point the roan pattern is not progressive with age. In fact, roans may darken with age. They may also change appearance with season, appearing lightest when the coat is shortest and darker in winter coat.

Corn marks (flecks of the base color) are common on roans, and scars often lack roaning. Photographs of wild horses often show this to an extreme, as dominance battles frequently leave extensive scars.

Roan is due to a dominant gene. At one time, the gene was thought to be a lethal when two roan alleles were present at the roan locus, but more recent work has shown this not to be true. The gene itself has not been found, but it is known to be near, if not part of, the KIT locus on equine chromosome 3. There is clear linkage with chestnut at the extension locus, and Roan on Seal Browntobiano is also linked. As an example of this, if a bay roan is bred to a chestnut, most of the foals will be bay roans or chestnuts, with only a few being chestnut roan or bay. Linked genes do not follow the rules of totally independent inheritance. A linkage test for roan is available if you want to know if a roan is homozygous.

Roan is quite variable in its intensity. Now and then a roan foal comes from two parents thought not to be roans, but close examination of the parents generally shows one to be a roan with very little roaning.

youngroansRoan may occur on any base color with any combination of diluting genes and marking genes. Black roans are often referred to as blue roans, bay roans as red roans, and chestnut roans as strawberry roans, but there are also references to purple roans, lilac roans, and honey roans. Further, a “red roan” could have either bay or chestnut as the underlying color, while some dark bay roans were called blue roan or purple roan. The modern practice is to put the base color first, followed by “roan.”

Roi (in Homecoming) will someday get a palomino roan mare with leopard (Appaloosa) markings—a horse overlooked by others because of her color but in fact quite a good horse. She is also a good example of the way different color genes can combine.

(The 3 photos on the left were taken at my cousin’s horse farm in Alabama.)