Horse Color Genetics: Seal Bay

Okay, I'm not going to do a review of all the letter sequences again, I'm guessing you will know what I mean if I refer to them.

One question that seems to come up a lot on a certain Facebook page for Equine genetics is, 'What is brown? Does it actually exist? And how do I define it as a color? How does it work genetically?'

First, let's talk about what brown actually is. When you think of brown, you may think of the color dubbed 'liver chestnut'.

This horse is pretty brown, right? There almost isn't another word for it. However, 'liver chestnuts' are genetically the same as a normal chestnut.

Kind of weird, I know, but true. So, back to the brown question. Does it actually exist? In a sense, yes. Well, the correct term for it is seal brown. What causes brown, and what does it look like?

While you may be confused, because this horse certainly doesn't look brown, that is only the name for it. It is also called seal bay, which is more correct.

Genetically, a seal bay (that is what I prefer to call them) horse has almost the same genome sequence as a normal bay. How do they look so different?

There is actually a different case between these than the first two chestnut horses. While they were very similar in genetic makeup and it was only due to how much black was incorporated in their coat, the bay's are different.

The difference is that the seal bay horse is the result of a different kind of agouti locus, abbreviated by At (actually, the t is supposed to be smaller). It isn't exactly a mutation, because many horse's have it, it is just a different kind of agouti gene. To non-genetic junkies such as myself, it is usually called dark bay.

One very confusing thing about seal bays is that they easily confused with black horses. Here are a couple pictures of both mixed together so you can see the confusion.

Just to help you lost folk out there, the first and third one's are black. They are, what you might call, 'fading black'. My own horse is a fading black, most black horse's are. Some happen to fade more than others. But can you see the difference? Most seal bays are lighter in areas such as the muzzle and flank area, while real black horse's tend to fade all along the belly and the muzzle will stay dark.

Just to put a smile on your face, here is a super cool Shire that is seal bay.