Horse of a Different Color? Part I
Color can be somewhat predictable...
How easy is it to predict what color your foal will be?
Well, here we are, ready to breed our horse or horses and we want to know what color our foal will be. We saw our friend's sorrel mare with a black foal by her side when bred to a bay stallion and we saw our other friend's black paint mare with a solid sorrel foal on her side when bred to a black paint stallion. It seems so confusing and we just want to know, what color will the foal be?
Luckily, it's not as confusing as it first seems. Horses actually come in two base coat colors. We will, for simplicity's sake call the first and 'dominant' of the genes 'black' and the second, recessive gene 'red'. You are probably thinking that this makes no sense, as you know horses come in a lot more than two colors. The good news is, you're wrong. There are really only two base coat colors in horses, black and red. All the other beautiful colors we see, such as paints, roans and dilutes like buckskins are caused by 'modifying genes' that act on the two basic colors. That makes breeding a little easier to figure out, although not 100% predictable.
All color genes, like most other genes, come in pairs, so a horse has a set of two. If one is dominant there can still be a recessive gene carried that does not show up. This concept is similar to a brown eyed person having a blue-eyed child. The blue eye gene in humans is recessive and is carried 'behind' the brown eyed gene.
In horses, we represent the dominant 'black' base gene with an E and the 'red' recessive gene with an e. This means a horse can be black =E and still carry the ability to produce 'red' foals which would make their base genetic color code 'Ee'. My stallion has this basic genetic code, (he is a bay, which we will talk about in a bit, because it's a modified black, but remember, the base is only two colors, black or red.) He is bay, which is a form of black, but his sire was a sorrel, so we know that he carries the recessive 'red' gene of his sire, making his basic gentic code 'Ee'. His sire's genetic code, as he is a 'red' or sorrel horse is ee. There is no black gene present.
Breeding two 'red' horses together will always produce a 'red' base coat, however, breeding two black horses does NOT always produce a black. That is because a black based horse, such as my stallion CAN carry a recessive red gene. That's where the red foal came from when your friend bred their two black paints together. Both horses were Ee gened and the foal turned out to be ee, or sorrel.
Horses can be homozygous or 'dominant' for the black gene also, which means they would have a genetic code of EE and would not be able to produce 'red' offspring. This can be a desireable trait when breeding, but there are other factors to consider if one wants to get black, rather than 'black gened' horses. As black can be modified, we have to look at some of the common modifiers to decide how best to predict our foal's coat color.
The most comon modifier of black is the 'agouti' or 'bay' gene. This gene pushes the black to the 'points' (legs, ears, mane, tail) of the horse's body and dilutes the body to a shade of brown. This is a common gene and so many horses who carry the black base either Ee or EE also carry the agouti. We use the symbol A if agouti is present and a if it is not. Like most genes, again, agouti is a pair, so a horse can either not carry agouti= aa or have one agouti gene= Aa which would push their black to the points, but they could still produce pure black foals, or AA which would mean that all of their foals would have some form of agouti dilution. This is a frustrating trait for those wishing to breed for black horses. However, pure black horses cannot carry agouti, or they would not be black as it pushes black to the points, so the best way to breed for black horses is to breed black to black. However, a black horse can carry a recessive red gene, so you may be surprised by a breeding to two blacks together to see a little sorrel foal appear in the pasture!
There are some other important modifying genes on horses that can all appear together or can be seperate from one another. The cream gene creates palomino on sorrels, buckskins on bays and a smoky black on a black horse, which is not always identifyable visually. The cream gene can be represented by Cr and N when not present, and like most genes, they come in pairs, so a horse with two cream genes is a 'double dilute' and will have blue eyes (but will not pass them on unless the foal receives two cream genes also) and pale skin. A double dilute will be represented as CrCr. These horses are often considered valuable breeding stock because they will ALWAYS produce dilute foals.
The dun gene is a modifier that produces beautiful and popular coat colors. It can be represented with D when present and N when not present. Horses with a pure black base coat will turn 'grullo' or 'grulla' which is a mousy grey or almost slate blue color with a distinctive dark 'dorsal stripe' and sometimes leg stripes, called 'leg barring' and stripes on the forehead (called spider webbing) and stripes over the withers as well. The more 'dun factor' a horse carries the more he or she will express the traits. A bay horse with dun factor will turn 'zebra dun' or 'bay dun' or some people also say 'yellow dun'. The horse will be a tan color with a dark dorsal stripe and the other charactaristics of the dun, usually with a black mane and tail. The 'red dun' is a sorrel horse with dun factor. This horse will be light orange to 'pinkish' in color with a darker dorsal stripe and the other charactaristics of the dun factor. Horses can be dominant for dun factor meaning they will only produce offspring with the traits as described above. Their genetic code would be represented as DD.
Another common modifying gene is the roan gene. The roan gene causes a mix of white hairs with the base coat color to make it look 'blue' on black horses or 'pink' on sorrels. These horses usually have darker heads and legs and normal colored manes and tails. The roan gene can be represented with R and N when it is not present. It used to be believed that all double dominant or homozygous roan horses died before birth, but now we know that this was just an old wive's tale. There are many RR horses alive and well, and they make valuable breeding stock because they will always produce roan foals!
A gene that is sometimes confused with the roan gene is the grey gene. This gene, Gr or N when not present modifys the horse's coat in a slightly different way to that of the roan gene, but can look similar at certain stages of the process. A grey horse's coat goes from a solid coat color (such as black) to a slowly all-over fading to grey and eventually white, sometimes with small spots which is referred to as 'flea bitten'. One way to tell the difference between a grey and a roan foal is that the grey foal will usually start to grey and lighten around it's eyes and the roan foal's head will stay dark but the body will lighten, especially around the flanks. It is not an exact science but along with the sire and dam's coat color it can usually be figured out. There are also homozygous grey horses who always produce grey offspring, this is represented as GrGr or GG.
There are also some rare coat color modifiers, such as the champagne gene. This gene works in a similar way to the cream gene, but is not the same gene. Horses often have hazel or greenish eyes, pale freckled skin, especially around the muzzle, eyes and genitals and a unique, metallic sheen. This can be a homozygous trait, but as the horses are fairly rare, and the trait descends from a few individuals in most breeds where it is known to exist, it's hard to find 'double dominant' examples, though there are a few.
There some other 'modifying' genes that occasionally occur in American Quarter Horses and American Paint Horses. However, due to them being extremely rare in the two breeds I will not discuss them in this short article. If you are interested in all the variations in coat color or in trying to predict what color your foal will be from a specific mating I suggest this website: http://www.animalgenetics.us/CCalculator1.asp which seems to be an excellent and well-reserached tool.
Horses can carry all or some of these color traits together, and for some breeders, the more unique color modifying traits a horse has, the more valuable he or she is as breeding stock because the horse is more likely to produce some kind of unique color that varies from the base coat colors. In my opinion, although all of the color traits are interesting and beautiful, the most important thing to focus on in any breeding program is quality, talent and personality and the color is secondary. If you can produce everything together then it's a bonus!
Part II will deal with paint color coat genetics.
Some examples of coat color modifiers
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