By Nancy Castle

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This article appeared in the Summer, 2004 issue of The Rainbow Morgan Horse newsletter,
and a partial printing of this article was published in the April, 2005 issue of The Morgan Horse Magazine.

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WHAT'S DUN IS DUN

By Nancy Castle ~ Dun Central Station
(Copyright 2004)

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Colorful Morgans are gaining popularity by leaps and bounds. And who can blame a person for admiring and appreciating a quality Morgan horse of a different color? It is a good time for the colorful Morgan, with several colors being saved from the brink of extinction, including gray, dun, and silver dapple. It is also a confusing time.

Colors can be very confusing since the genetics of various colors have long been misunderstood, and look-a-like colors add to that confusion. Unfortunately, the internet is full of information that is not necessarily correct, and most of the equine color books currently on the market are outdated, or fail to be written in a way that the average person can even begin to comprehend. It can take a lot of studying, research, and sifting through outdated and incorrect information, and not just a little bit of hair pulling, to figure out how some of these colors work, and which are look-a-likes.

One of the most daunting tasks is the proper identification of color. Even within the "normal" colors, one can find chestnuts that are so dark they appear to be black, for example. It is no wonder that we are finding a number of Morgans mistakenly identified as an incorrect, and often impossible color given their parentage. This certainly applies to the dun colors. This article should help remove at least some of the mystery and hopefully aid in avoiding future errors.

The dun colors are the result of the dun dilution gene's unique affect on the basic base coat colors. The four basic base coat colors that we will be talking about are black, brown, bay, and chestnut. Traditionally, only three base colors are recognized; black, bay, and chestnut. However, the results of research done by a group of French researchers has shown that there is a slight, but important, genetic difference between bay and brown, as well as the visual differences, so for the purposes of this article, we will separate these into two base colors.

The genes that create bay and brown are called agouti genes. The agouti genes are modifiers that restrict black pigment on a horse whose base color is black. Chestnut horses, and colors derived from chestnut (such as palomino and red dun, for example), are not visibly affected, as they have no black pigment to be restricted. Chestnut base colored horses can, however, have agouti genes and pass them on to their offspring. While both bay and brown caused by agouti genes restricting black, there are two separate forms of the agouti gene. In a nutshell, the difference between bay and brown is that the specific form of the agouti gene that causes bay has a "stronger" effect than does the form of the agouti gene that causes brown. This simply means that the bay form of agouti is "stronger", so it restricts the black more completely from the body, while the brown form of agouti is "weaker", thus only restricts the black from limited areas, such as the muzzle/nose, flanks, elbow area, and the insides of the upper legs sometimes. As anecdotal evidence has shown, these two different forms of the agouti gene do inherit separately from each other, so they are not simply the exact same gene randomly expressing differently from one black based horse to the next. More detailed information about the genetics of these two forms of the agouti gene would be better left for another article, though.

Now, back to the dun (dilution) gene. The dun gene is not related to the cream gene at all. The cream dilution gene gives us smoky blacks, brown (or seal) buckskins, buckskins, and palominos, as well as the double cream dilute colors of smoky cream, perlino, and cremello. You cannot produce a dun colored horse from horses that are one of the cream dilute colors just mentioned. However, it is possible to have horses with both cream dilute and dun dilute genes, if one of the parents was a dun, or a dun plus cream dilute color. For example, a buckskin that also has a dun gene is most often called a dunskin, and a palomino with a dun gene is generally called a dunalino. But like the cream gene, the dun gene is dominant. This means that for any horse to have a dun gene, at least one of its parents must also have a dun gene. It also means that if a horse has a dun gene, the gene will be expressed, and the horse will be one of the dun, or dun plus cream, colors.

So how can you tell if your horse has the dun gene or not? That's the tricky part! It's rather tricky because there are markings that mimic the markings required of dun colored horses. These are usually referred to as counter shading markings. But first, we should focus on exactly how the dun gene affects each base coat color, and defining the various colors of dun.

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