Equine Coat Color Genetics

Lesson Five

Wrapping up Dilutions

You will remember that the term “dilute” is used to describe many colors: basically any of the colors that result from a dilution (lightening) of the color. These are all caused by different genes. We have already covered Cream, Dun, and Champagne. In this lesson, we will cover Silver, Pearl, and talk about various mixtures of two or more dilution genes.

The Silver (AKA Silver Dapple) gene

Silver is a simple dominant; there is no visual difference whether the horse has one Silver gene or two. The symbol for this gene is "Z" (nobody seems to know why that letter was chosen, but "S" would have been confusing since many colors begin with that letter, and maybe just about everything else was taken). The gene was isolated in 2006, and there is now a test for it.

This color has been known for 30 years or more, but is only recently becoming better understood. The name Silver Dapple was originally applied to Shetland Ponies, in which the color is fairly common (at one time it was even thought that the gene only occurred in Shetlands), because it frequently has the extremely dappled, greyish body color with silver-white mane and tail in that breed. Now we know that not all (possibly, not even most) of them are dappled, so the name has been shortened from Silver Dapple to just Silver. The term "Silver" has been confusing to some, who expect to see a grey-toned horse perhaps, but it has been in use too long to change. In Australia the color is called "Taffy", but the term has never caught on elsewhere. In some of the breeds in which Silver is common in the USA, such as the Rocky Mountain Horse, it is called "Chocolate". Except in the few breeds where it is common, they are almost always registered as chestnut.

This color is not frequently seen except in a very few breeds -- the Shetland, Mini, and Icelandic have quite a few, and there are a few breeds in the USA which have purposely selected for the color so that now many horses of those breeds, perhaps even most in some cases, are silvers: the Rocky Mountain Horse, Mountain Pleasure Horse, and Kentucky Mountain Saddle Horse. Aside from those breeds, it is not a very common color, but it does occur in the Welsh Pony, Welsh Cob, Quarter Horse, Paint, Appaloosa, Morgan, Saddlebred, Tennessee Walker, Missouri Foxtrotter, Bashkir Curly, Mustang, Dutch Warmblood and Paso Fino. There are even reports of it possibly occurring in the Arabian, but these have never been proven. It is thought to have been in the Friesian breed in the past, but no longer. It also is known to occur in some draft breeds such as the Belgian, Breton, Comtois, Noriker, and Italian Heavy Draft.

How it works

The Silver gene is interesting because, unlike Champagne and Dun, which we covered last time, Silver is more like Cream in that it is pigment-specific. Silver dilutes only black pigment. Thus, the Silver gene can be carried and "hidden" by a chestnut horse (since it has no black pigment to be diluted), and in this way it can appear to skip generations, even though, like any dominant gene, one parent must have the gene in order for the foal to have it. It is like the opposite of Cream, which only dilutes red pigment when heterozygous, and thus can be carried and "hidden" by a black horse.

When a horse gets the Z gene, any black pigment will be diluted to a chocolate-brown, ranging in shade from taupe or "dead grass" color through mocha-brown to deep chocolate brown, often with a bluish cast. It can be hard to tell apart from a dark liver chestnut, but usually the dark chestnut will have reddish undertones and the Silver will not. The gene tends to dilute the mane/tail much more strongly than the body, often to a silvery-white color, although this can vary and they may darken with age. Silvers often have a distinct "face mask" of darker hair which is helpful in identifying them. This "mask" generally covers the forehead, around the eyes, and down the front of the nose. They also tend to have lighter hair on the lower legs, lightest close to the hooves. Another interesting feature of this color is that it is very often markedly different in summer and winter coats, or if a horse is clipped.

Silver on Black

Silver on a black base color is the shade that comes to mind first when hearing the term "Silver Dapple". The body color is diluted to a chocolate-brown or mocha-brown shade, sometimes light enough to appear similar to a sooty palomino. The mane and tail are often near-white, a striking contrast. The lower legs are usually lighter than the rest, almost flaxen near the hoof, and the lower legs are often dappled (which is highly unusual in other colors). The mane and tail often have dark roots. In a horse with the "classic expression" of Silver Dapple, there will be very distinct and strong dappling present, which, unlike most colors, does not appear to be related to age or condition, but rather stays fairly constant throughout the horse's life -- although they may vary with the seasons, appearing on the summer coat but not the winter coat, usually. But not all Silvers show the dappling. Some are a flat chocolate-brown color all year round. Silver on black can be hard to tell apart from a dark flaxen liver chestnut, and in most breeds they have indeed been registered as "chestnut" because nobody knew what they were. Some clues to look for would be the dappling, a drastic change in color from winter to summer, a bluish cast rather than a reddish tone, and a silvery mane/tail rather than golden-hued flaxen. Still, it may be impossible to tell the difference by looking. Thankfully, there are now genetic tests that will tell for sure. The normal name for this color is "Black Silver", but sometimes you might see them called "Classic Silver Dapple", "Chocolate Silver", "Chocolate", or just "Silver".

Typical Black

Typical Black Silver

Silver on Bay

The Silver gene acting on a bay base color gives a quite different effect. The red pigment on the body is unaffected, while the black on the legs is slightly diluted and the black of the mane/tail is more strongly diluted. This gives the appearance of a horse that is not quite bay, and not quite chestnut either. Most of the time they end up being registered as chestnut, which can cause confusion, but most registries have no separate category for Silver. The mane and tail can vary from a platinum blonde, to a flaxen color, to just slightly diluted, and can darken considerably with age, making identification more difficult. Usually the legs are the main clue that the horse is not a chestnut -- they will be much darker than a chestnut, ranging from near-black to chocolate-brown, generally with lighter hair close to the hooves. And again, when in doubt, testing will distinguish them from chestnuts. The most usual term for this color is "Bay Silver" or “Silver Bay”, but occasionally they are called "Red Silver" (reflecting the reddish body color), however, this is discouraged, since to most people the term "red" means chestnut, and therefore "red silver" could cause confusion to those thinking that it means silver on chestnut.

Typical Bay Bay Silver Bay Silver

Silver on Brown

A seal brown with the Silver gene will look similar to either a black silver, or a bay silver, depending on how light or dark the brown's base color happened to be. Most seal browns are mostly black, and this plus Silver would probably be very hard to tell apart from black silver. There would likely be some tan on the muzzle on close inspection. The lighter seal browns with more tan in the coat would give a lighter shade of Silver. Testing for the different Agouti genes might be needed to be sure. The most usual term for this color is "Brown Silver" or “Silver Brown”, but if the exact agouti genes are not known, they might be called by whichever they looked most like, i.e. Silver Bay or Silver Black, or just called Silver Dapple.

Typical Seal Brown Brown Silver

Silver on Chestnut

Since a chestnut horse (or any other red-based color) has no black pigment to be affected by the Silver gene, they will show no effects. Such a horse would be called "chestnut carrying silver". Some breeds use the term "Silver Chestnut" but this is highly discouraged by geneticists, because it tends to confuse people, making it sound like the chestnut horse is somehow affected by the Silver gene. In some breeds, some breeders apparently think that the Silver gene can cause a flaxen mane/tail on a chestnut horse; however, this is not true.

Foal colors

Foals often have hooves with a very strong and distinct striping pattern, and white eyelashes. These traits are helpful for identifying Silver in foals, but are gradually outgrown most of the time. Bay and brown silvers generally look chestnut as foals, and black silvers typically are a greyish color at birth. The diluted mane and tail may not come in for some time. One thing that is helpful in identifying Silver foals is the fact that they will be born with black skin (since they have an “E” gene) rather than pinkish skin which is typical on chestnut (or other “e/e”) foals at birth. Now that the gene has been isolated, of course, we can test for it and not watch and wait and wonder!

Breeding for these colors

As a simple dominant, only one gene is needed to get the color. Therefore, you have a 50/50 chance of getting it when breeding a heterozygous Silver to a nondilute.

Punnett Square example:

	Z	z
z	Z/z	z/z
z	Z/z	z/z

And when breeding two heterozygous Silvers, you will get 25% homozygous Silver, 50% heterozygous Silver, and 25% nondilute.

Punnett Square example:

	Z	z
Z	Z/Z	Z/z
z	Z/z	z/z

However, because of the pigment-specific action of this gene, when a chestnut is involved, it can mess up the percentages. A chestnut can carry the gene, but won’t express it. So if you have, say, a black silver who is “E/e”, bred to a black who is also “E/e”, rather than the straightforward 50-50 chance of black or black silver, you instead have a 25% chance of chestnut (half of which will have the Silver gene, but not show it), 37.5% chance of black, and 37.5% chance of black silver.

The Pearl Gene

Pearl is a fairly newly discovered gene in the dilution category. This gene is almost certainly a third allele at the Cream locus, but at this time the research showing that has not been published. We should assume it is, until proven otherwise, since the evidence is quite strong. U.C. Davis, who developed the test, is calling it "Prl". The test has been available since October 2006. This gene is not quite a simple recessive gene, but almost. It normally requires two copies to be visible by itself, but it also is visible when one Pearl is combined with one Cream allele.

History:

In November of 2001, the registrar of the Champagne registry (ICHR), Carolyn Shepard, received an application for a Paint horse named "Barlnk Peachs N Cream". She looked for all the world like a gold champagne, complete with golden coat, pink skin and freckles. Just one problem -- her parents were both "sorrel". It's not all that uncommon to find a gold champagne that was registered as chestnut/sorrel, likely as young foals while still in their darker baby coat, or maybe they are a particularly dark shade. But in those cases usually the horse will have a champagne parent, or other champagne offspring. This was not the case with these parents. No other explanation could be found, though, and it was before any tests for these genes were available. So the horse was given a "tentative" number (meaning she would have to prove she was truly champagne before being officially registered). But this oddity sent Carolyn Shepard on a quest, and what she found was that there were increasing incidences of "palominos" popping up from two "sorrel" parents, and double-dilute-looking foals from one non-dilute parent. What they all had in common was that they were descendants of a horse named Barlink Macho Man. She was convinced that this was a new gene. She called it the "Barlink Factor" and by July of 2002, had figured it out enough to write an article about it (which is still available on the ICHR website).

Meanwhile, some odd-colored horses were popping up occasionally in the Andalusian and Lusitano breeds. It was hoped that they might be champagne, which is what they looked like, but as with the similar Paint horses, no champagne ancestor could be found, and they didn't reproduce the color as expected. Eventually it seemed there was no other explanation than that this was a previously unknown dilution gene. By consensus of those researching it, it was called "Pearl". You can read more about the process of finding and identifying these horses at www.newdilutions.com .

The genetics researchers at U. C. Davis heard about the "Barlink Factor" and wanted to try to find the gene. Carolyn Shepard, by that time, was certain that it was an allele at the Cream locus, or perhaps a gene right next to it, because by then there were several known "Barlink Creams" which were thought to be cremello/perlino but did not produce like one -- instead of having 100% diluted foals, they were passing on only the Cream, or only the "Barlink Factor" (which caused an undiluted-looking foal) -- never both at the same time. She told the lab at U.C. Davis about her theory and told them where to look for the gene. And, sure enough, they found it in record time. (By comparison, all of the other color genes that have been isolated took several years of searching.) They announced that a test was available in October 2006. They would not call it "Barlink" since the owner of the Barlink-related Paint horses was against the idea, and also, by then it had been found to have come from the mare My Tontime (granddam of Barlink Macho Man). U.C. Davis proposed calling it "apricot", to howls of disgust from horse owners and color researchers everywhere. But a surprise was yet to come. In late October, they tested a hair sample from a "pearl" Andalusian, and it turned out to be the same exact gene! So, to the relief of all concerned, they settled on "Pearl" as the official name for the gene.

Some would say that the gene is not "official" yet because they have not yet published the study. But many horses have now been tested, and the results have all been consistent with their phenotypes and pedigrees. It's also not considered "official" that the gene is located at the Cream locus, because U.C. Davis has not yet confirmed this in writing. But those who have researched this color extensively are 100% sure that it is. There have now been a large enough number of horses with offspring to say that the Cream/Pearls have never been observed to pass on both genes, only one or the other. And no horse has ever been found to have two Cream plus one Pearl, or two Pearl plus one Cream. By now most feel the evidence is overwhelming, it just can't be stated "officially for sure" until that study is published.

So far the Pearl gene has been documented in the Paint horse (so far only in descendants of My Tontime), the Andalusian/Lusitano (in both America and Europe), the Peruvian Paso (in 2006) and the Gypsy Cob (in 2007). Undoubtedly more will follow, now that the test is available to identify carriers. We would expect to find it in breeds with Spanish influence, such as the Mustang, Appaloosa, and Quarter Horse, and possibly some of the gaited breeds. It is presumed to be a mutation of the Cream allele that happened at some time in the Iberian breeds, and from there spread to America. It does appear to be quite rare, but considering how it can be carried for many generations without being visible, it is unknown how widespread it might be.

How it works

All of the dilution genes have something that makes them unique, and Pearl is a quirky one. It does not appear to be pigment-specific like Cream and Silver, that is, it dilutes both red and black pigment equally (like Champagne and Dun). It does not leave the points dark, or put stripes on the horse, like Dun. It does dilute the skin color, like Champagne. But it only causes a visible dilution effect when there are two Pearl genes, or one Pearl and one Cream.

One Pearl gene by itself does not dilute the base color, although the horse will usually have pink speckles on the skin. These are not always present, and may come and go over time, so it's not a definitive indicator of the gene, but it is commonly seen. One Pearl gene does not appear to have any additional diluting effect on horses with another type of dilution gene. It does not create a “double diluted” look when combined with Champagne, as Cream does. There are a few documented Pearl + Champagne and Pearl + Dun horses, and they don’t look any different from ones with no Pearl.

One Pearl gene plus one Cream gene gives a horse that is usually born looking like a cremello or perlino, but looks more like a champagne-cream as it gets older. They often have light colored eyes (but not typically bright blue as adults), and they have pink skin like a champagne. These horses are easily mistaken for double-cream dilutes or champagne creams. On a red base, they look like a cremello or a gold cream. On a bay/brown/black base they look very much like a perlino or light amber cream.

Two Pearl genes will dilute both the hair and skin so that the horse looks remarkably like a champagne. Most of the ones that have been found are on a chestnut base (since that color is so common in the Paint breed) and they look like a gold champagne. They are golden, with pink skin and freckles. They have been registered as palomino. A homozygous Pearl on other base colors looks very similar to a champagne of that shade.

Breeding for these colors

When breeding two heterozygous Pearl carriers, which carry no other dilution genes, together, there is a 50% chance of getting a Pearl carrier, 25% chance of getting a visible Pearl color, and 25% chance of no Pearl gene. This unexpected result is what led to the discovery of the new gene. When people started linebreeding to the popular stallion Barlink Macho Man, these “palominos” from two apparently sorrel parents, and “cremellos” with only one dilute parent, started popping up.

When breeding a heterozygous Pearl carrier to a heterozygous Cream color, you have a 25% chance of getting both (the horse would appear cremello/perlino), a 25% chance of single Cream dilute with no Pearl, a 25% chance of a Pearl carrier with no Cream (will not be visibly diluted), and 25% chance of no dilution genes.

If that Cream + Pearl horse (which generally has the phenotype of a double Cream dilute) is bred to a nondilute, he will pass on either the Cream gene (giving a single Cream dilute phenotype) or the Pearl gene (giving a nondilute phenotype), because these genes are at the same locus, which means any horse can pass on only one to each foal.

Double Pearl on chestnut. Bother parents are normal-looking chestnuts, who carry a Pearl gene.

Another Double Pearl on chestnut, but a much lighter shade.

Close-up of skin color; very champagne-like.

Dilution Mixtures and Confusion

When a horse happens to inherit more than one type of dilution gene, the results can be highly variable. Some of them combine to give a “double dose” effect, while others have no visual effect at all. Some combinations even tend to create a darker color than either one would give alone, oddly enough.

Silver Combinations

When Silver and Cream are both present, the effects of the Silver gene tend to be less obvious, or even not really visible at all. This would seem to be counterintuitive since Cream makes the mane and tail of a palomino white, and Silver makes the mane and tail of a black silver white (or nearly white, usually), but oddly enough they seem to almost cancel each other out instead of doubling the dilution effect.

When Silver is combined with Dun, the horse will usually have about the same body shade as with Dun alone, with the darker dun-factor markings, but with a light mane and tail like a typical Silver, and the black on the legs will be somewhat diluted and often dappled or mottled. (A red dun would of course show no visible effects.)

When Silver is combined with Champagne, it gives a boost to the overall level of dilution (although not to the same extreme as combining Champagne and Cream) and dilutes the mane, tail, and legs. The examples that have been found so far are similar in shade to a smoky cream. Unless it is known for certain which dilution genes are present in the parents, only genetic testing can sort these out, since they look very similar.

Amber champagne plus Silver

Dun vs. Buckskin vs. Dunskin

Probably one of the biggest areas of confusion is in this group of colors. Throw in a few amber champagnes and it gets even worse. Part of the problem comes from the fact that, for many years (and even today in some places and some breeds) all kinds of dilutes were lumped together under the name of "dun". So when you hear someone say "I didn't know I could get a palomino foal from a dun," well, technically you can't... but since buckskins are/were commonly called dun, suddenly it makes perfect sense.

If horses followed all the "rules" it would be much easier. Things like "all champagnes have pink skin" (they do, but it can look awfully dark from a distance and in photos, especially when heavily freckled by the sun). Or "duns have dorsal stripes and buckskins do not" (not so, buckskins can have surprisingly dark dorsal stripes on occasion). Or, "it's not a dun if it doesn't have leg barring" (generally true, but sometimes those markings are obscured by pinto spots, or invisible on a really light color like cremello).

Usually looking at the pedigree can be helpful when there is doubt. Some breeds only have one or the other kind of dilution, and in others there are well-known lines of dun and cream and champagne. Assuming the pedigree is correct (no "fence jumpers"), this can often be all the info you need. Other times it's just not known which kind of dilute the ancestors were, or maybe they were both.

Duns and dunskins will have the dorsal stripe and leg barring (unless there are white markings covering those areas). A dun dorsal stripe tends to be more reddish colored, very sharp-edged (typically people say it looks "painted on" or "like it was drawn with a Sharpie"), slightly wider over the loin area, and runs right down the center of the mane and tail. A non-dun dorsal stripe tends to be black in color, be the same width throughout, be rather fuzzy-edged, and sometimes comes and goes with the seasons.

Probably the main thing to look for to identify a buckskin with a dorsal stripe is the lack of any leg barring. If there is none, that pretty much rules out dun. But if the horse has some ambiguous "mottling" on the legs, or high white that covers that area, then the only way to know for sure would be by testing. Thankfully, we now have a dun test!

Regular bay duns and dunskins can be impossible to tell apart by appearance only. Dunskins tend to be lighter in general, but there's such a wide range of shades from light to dark in both colors that they do overlap quite a bit. Sometimes the pedigree will have the answer (i.e. if one parent was a cremello or perlino, there must be a cream gene, etc.) but sometimes, testing is the only way to know for sure.

Buckskin dorsal stripe

Dun dorsal stripe

Palomino vs. Dunalino

Palominos sometimes have dorsal stripes, but it's usually the dark, sooty ones that show these, and they are not sharp-edged stripes. Dunalinos are often somewhat lighter than the average palomino (depending on the shade of chestnut that is their base color), usually with a somewhat muted “peachy” tone, have distinct red-colored dorsal stripes, and red leg barring. Some dunalinos are the same shade as a regular palomino (perhaps these would have been darker palominos if they didn't have a dun gene), and the dun-factor markings are only noticeable on closer examination. It's also worth mentioning that, in some breeds, owners of dunalinos are not willing to accept or disclose that fact, preferring to call them palomino. (There is a Palomino registry that does not accept dunalinos.) And for registration purposes, they have to choose whether to call them palomino or red dun. It is very rare for a dunalino to appear "sooty". It does happen occasionally, but usually just in foals during a shedding phase. They are also hardly ever dappled.

Dunalino dorsal stripe

Dunalino

Grulla vs. Smoky Grulla

These two colors cannot be told apart by appearance only. Smoky grullas may be somewhat lighter, but not always. Many are just as dark as regular grullas. The only way to know for sure is if one parent was a double-cream-dilute, or if the horse has produced a definite cream dilute foal, or if it has been tested.

Grulla vs. Smoky Black

These two colors in theory should be pretty easy to tell apart, but it's an unfortunate fact that many smoky blacks have been registered as grulla over the years. So, if you see "grulla" in a pedigree, it may require a little more research to be sure that it was in fact a dun-dilute and not a cream-dilute. Smoky blacks can do a very good grulla imitation at times. Especially as foals, when they may have "foal-coat markings" that often look a good deal like dun-factor markings (but they go away when the foal-coat is shed), or when they are sun-bleached. Here is a picture of three smoky blacks and one grulla. Can you tell which is which? On close inspection it's easy to tell that only one has a dorsal stripe and leg barring, but from a distance or in pictures, it's not so easy. (The second from the left is the grulla.)

Champagne Mixtures

Once you see a champagne up close in person, you will never again understand how anyone could confuse them with a cream or dun dilute. The skin color is just so totally different. But if all you have is a photo, it can be hard to tell. Pictures can be deceiving.

When champagne is combined with cream, it often produces a pretty good imitation of double-cream-dilutes. The illusion is strongest when they are foals. As they mature, the eyes will change from blue to amber, and the skin will begin to freckle. Interestingly, many champagne creams have even more and darker freckles than regular champagnes.

When champagne is combined with dun, the results are what you'd expect -- a champagne colored horse, usually lighter than normal, and with all the dun-factor markings. Where it gets interesting is when cream is added to the mix as well. It would seem logical that the champagne/dun/cream horses would be lighter than the champagne/dun ones, and sometimes they are, but it's not always the case. Some champagne/duns are in fact lighter than some champagne/cream/duns. It must be that the range in shade from light to dark of the base color causes these mixtures to have overlapping phenotypes. So, in cases where either one is possible from the pedigree, the only way to know for sure is by testing them.

Chocolate Palomino vs. Silver Dapple vs. Flaxen Liver Chestnut

These colors can look remarkably alike, for such very different things. They can readily be sorted out with genetic testing nowadays, thankfully. No more guesswork like in the past, or waiting to see what kind of foals they produce. But if you are looking at a horse where testing is not possible and you just want to make the best possible guess, here are some clues to help figure it out.

Silver dapples don't always have the dapples for which the color was named, but when they do, the dapples are quite vivid and clear, and often continue down onto the lower legs (something quite rare in any other color). Chocolate palominos are often, but not always, dappled as well, but these dapples tend to look more like "normal" dapples and often change with the seasons. Dapples seem less common on liver chestnuts. Silver dapples often have dark roots in the mane/tail hair. And the "tone" of the color will often give a clue. Silvers usually have a "cool tone" to their coats, with an almost bluish cast, with manes and tails typically described as "silvery" or "platinum" (although they can be quite dark too). Chocolate palominos usually have a yellowish tone, often with lighter golden shading on the face, with manes and tails that are white but often with varying amounts of dark sooty hairs mixed in. And liver chestnuts usually have a reddish tone to their color, and typically a more yellowish tint to the mane/tail color.

In the days before genetic testing was available, the only way to sort these out was by close examination of the individuals, their parents and siblings and offspring, and looking for patterns in their pedigrees. (For instance, silver dapples registered as chestnut can be the cause of a bay from two chestnut parents – which would be impossible if they were truly chestnut, and a “chestnut” producing a cremello must be a dark palomino.)

Which is which??

From left: silver dapple, chocolate palomino, liver chestnut

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