Tag Archives | wild bay

Bay is not a modifier

OrdinaryBay

When talking about a topic as complex as equine coat color, simplifying concepts is essential. This is particularly true when speaking to a non-technical audience. The trick is to avoid more detail than is necessary without reducing the topic to the point where the information is misleading or inaccurate. Ideally any simplified explanation is compatible with a more nuanced understanding, since it needs to provide a solid foundation for those listeners who want a more in-depth understanding of the subject.

One of the common conventions used to explain horse color is that of basic colors and modifiers. By structuring the explanation this way, it is easier to make sense of the wide variety of colors and patterns. When each color is understood to have three (or four) versions—chestnut, bay/brown, and black—it is easier to see the relationships between colors that are not visually similar. The other advantage to this system is that, because the basic colors are a given, you get to skip (or at least gloss over) the mechanics of basic coloration in horses. That is useful because the basic colors require a more complicated explanation than most of the dilutions and white patterns.

In an attempt to simplify basic colors, one approach that has become increasingly common in internet discussions is to move bay into the “modifier” category, and assert that horses are basically red and black. Bay, by this convention, becomes a modifier of black. In the “absence of agouti”, the explanation goes, a horse is black. This approach is problematic on a number of levels, not the least of which is that it obscures the fact that “agouti” (as it is used in horses) is a genetic locus. It is a place in the genetic code, and not the name of a specific color. (The term is used for specific colors in other species.) There is no “absence”, because all horses have Agouti (ASIP). Some of them have the allele at Agouti for bay (A).

Tahki1
A study of ancient remains showed that bay was the original color of horses. At the time it was not possible to test for dun, but based on the pervasiveness of dun in wild equids—like this Przewalski’s Horse—it is assumed that they were likely bay dun.

It also takes a concept that is really about pigment, and applies it to the horse. Pigment in mammals is understood to be basically red (or yellow) and black. At the animal level, though, animals are understood to have a wild color that is typically some combination of those two pigments. In horses, that wild color is not red (chestnut) or black, but bay. Bay—or more likely bay dun—was the original color for the species. Animals that are all-red, or all-black, are usually the result of mutations to (modifications of) the species’ original color. Presenting bay, the wild color for horses, as a modification of black gets this backwards. Black is not the default color, but a mutation to the Agouti (ASIP) locus that could have occurred as early as 5200 BCE. Samples from 9210 BCE and earlier were uniformly bay.

It requires more explanation than the “all horses are red or black” approach, but the basic colors are governed by a category of genes that control pigment-type switching. That is because pigment cells have the ability to produce both types of pigment (red or black), and these genes are what control the switch between the two possibilities. One of the clearest explanations of pigment-type switching can be found in The Colors of Mice: A Model Genetic Network:

Pigment-type switching describes the ability of pigment cells to switch between the production of eumelanin [black] and pheomelanin [red], under the control of the Agouti and Extension loci and modifying genes.

In horses, Extension is sometimes called “the black gene” because its dominant allele (E) is responsible for the colors often referred to as “black-based” (bay, brown and black). That term is somewhat misleading, however, because it does not mean the horses with that allele are “basically black”, but rather than the resulting colors have some portion of black in the coat. It is a category based on the presence of black, not on modification from an all-over black color. Despite its popular name, the dominant form of Extension (E) does not just produce black pigment, but rather black and red pigment. (Remember that pigment cells already have the ability to produce either type.)

For those horses that can have both red and black pigment (E), the alleles at Agouti control which parts of the horse will be black. Agouti does not “add red” or “dilute black to red”, which are the two common assumptions made when Extension is presented as giving either a black (E) or a red (e) horse. There is a recessive mutation to Agouti (a) that distributes black over the entire horse, effectively eliminating the red pigment, but Extension itself does not limit cells to producing only black pigment.

I understand the appeal of simplifying the situation with black and red pigment, but I do think that the distinction between basic pigment colors and basic horse colors is an important one. Because there are some unknowns in this area of color genetics, and because there have been surprises in other species, it is probably helpful to lay the foundation for pigment-type switches as a general category. That means being clear about the situation with Extension and Agouti, even if it takes a little more effort to explain.

WildBay4
This variant of bay, known as wild bay, involves a reduction of black pigment at the points, particularly the legs. It is presently assumed to be an allele at Agouti, but that has not yet been proven.

Note: I would like to talk about some of the pigment-type switching “surprises”, because there have been some fun discoveries in that area in recent years, but that will require wandering a little further afield so I’ll save that for a future post.

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Frosted Buckskins

FrostMan

I am still sorting through some of the old photos I have, trying to remember what has been posted (as opposed to “meant to post but never did”). If I repeat something, please forgive me - though I would imagine that if after three years I cannot remember posting about a subject, maybe readers have forgotten it, too!

Recent conversations about flaxen-maned bays reminded me that I had meant to post these pictures of buckskins with frosted manes and tails. As the photo above shows, the hairs are pale flaxen or white. It is harder to tell because the pulled mane on this Paint gelding is so short, but most of the time the pale hairs are short, which gives the mane a frosted look. Pale hairs are also seen at the tailhead. This next picture shows the distinctive “V” shape that is typical of the frosting on a buckskin’s tail. This shot also shows more clearly how the white on the mane is concentrated at the base of the neck.

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The frosting on the tail looks quite different from that kind often seen on duns. With a dun, the paler hairs are usually found on the sides of the tailhead, in part because the dark pigment of the dorsal usually runs down the core of the tail.

DunTail

Both frosting on buckskins and on duns looks a bit different from the white “coon tail” seen on some of the white ticking and sabino patterns. With this picture you can see both the paler hairs to the sides of the tail (relative to the deep red dorsal stripe) and the white hairs that are part of the patterning.

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Frosting is more common in duns than in buckskins, but it is not always pronounced. This dun mare has very little contrast – just a few paler hairs – between the core of her tail and the sides.

DunTailhead

So what causes frosting on a buckskin? Most likely it is the Cream (Cr) gene turning what would be paler red guard hairs to a pale flaxen or white. This photo shows the similarity between the arrangement of the pale hairs on a light bay and those on a frosted buckskin.

CreamFrost

Here is the same bay Paint Horse mare that is pictured above. She has the reduced intensity at the points that is often seen on bays with paler hairs at the base of the mane and tail. If you look closely, you can see the lighter hairs at the base of her mane, too. (Unfortunately she was always on the wrong side for the sun, so none of the photos taken from her other side turned out.)

GuardHairs

I suspect that selecting for this kind of clear bay with reduced black points would increase the contrast on the frosting of both buckskins and duns. That is probably why frosting is so typical of the Fjord. That breed appears to carry almost every factor that might reduce black points.

The downside of frosting on buckskins is that is does not appear to be permanent. As the horses age, they seem to lose the contrast until their manes and tails are black. At least, that has been my observation based a limited number of individuals. Certainly if a reader has an older buckskin that still has pronounced frosting, I would love to hear from them!

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More flaxen-maned bays

ShquestaStand

Although silver tails – Gulastra’s Plume from the previous post – are perhaps better known, bay Arabians appear to have a range of flaxen or silver mixtures in their manes or tails. This Arabian mare, Shquesta, has another combination that I have seen in at least one other Arabian. Her mane has a mixture of silver hairs. From the distance in this photo, it might be mistaken for sun-fading. Up close it is more obvious that a small percentage of her mane grows in silver.

Shquesta4

Although her tail is normal, the white hairs are not limited to her mane. They are also present on her pasterns. The hairs are more pronounced on the hind feet than the front, though they are present on all four legs. The photo to the left was taken in the late fall, and the one to the right was taken in the summer. She has no other white markings.

Shquesta is in her teens. In the six years I have known her, the portion of white hairs have not changed by any noticeable amount.

Shquesta5

The other Arabian I had seen with this same kind of mane silvering was the Courthouse Stud stallion Benjamin (by Champurrado). I had only seen him in old black and white photos, but the silvering was always visible. What I had not noticed, until I met Shquesta and pulled out those old pictures, was that he also appears to have silver pasterns on his unmarked forelegs.

Shquesta and Benjamin are pretty subtle. There have been bay Arabians with silver manes and tails that are far more pronounced. Most recently these have included the mare MP Festival. Her sire Stival has a flaxen mane, though it is less pronounced than here. She is probably the most dramatic of the flaxen bay Arabians.

MP Festival is what most people would call a wild bay. That is, a bay with very reduced black at the points. In the last post the question was raised whether or not the pony with the silver tail was just a wild bay. That is a very good question. Just what is the relationship between these flaxen points and wild bay? Certainly if silver is ruled out, flaxen manes on bays are much more common in breeds where wild bay is seen. Yet some horses like Shquesta do not really look like obvious wild bays. And there are also bays with reduced black on the legs that have a fully black mane and tail. Shquesta does not have deeply pigmented black legs of the kind that some bay horses have, but they are more filled in than what most would call wild bay. But where does the line get drawn?

Is this elderly Arabian, Omi, a wild bay?

Omi1

Notice that his lower legs turn silvery at the heels in the back, and just above the fetlocks in the front, much like many wild bays do. Yet his mane and tail are completely, deeply black. (All the white hairs on his face and neck are from age – he is in his mid-to-late twenties here.)

Omi3

Compare the points on Omi to those of the Miniature Horse, Thumper. He is an appaloosa, so the silvering on Thumper is unrelated to his shade of bay, but Thumper is an excellent example of what the points on an unquestionable wild bay look like.

ThumperWild

Here is a close-up of his legs that show the limited nature of the black on his legs.

ThumperWild2

So the question is, “What is the full range of black points on a wild bay? What is the upper limit for the black on the points?” Of course, it would be helpful if there was a test for wild bay, as there is for brown. Being able to rule wild bay in or out would be helpful in assessing the relationship between it and flaxen manes and tails.

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