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More mimicry

June 8, 2021 0 Comments

This post first appeared on July 10, 2011
Horses like this one often get labeled as sabino-rabicanos. The high stockings with their irregular edges and the wide blaze that travels under the jaw are typical of horses with the sabino pattern. The reason many people add rabicano to the description is the roaning on the flank and the white on the tailhead.  Here is a better angle to see that trait.

The trait is sometimes called “coon tail” because the roaning can take on a banded appearance. This horse has banding that is a little more pronounced than the first horse. (It can be even more noticeable on some horses.)

Here is a sabino with roaning right in the area rabicano tends to concentrate. A close up of this horse appears at the top of this post.

The problem with this is that a lot of sabinos have these traits, too. Both flank roaning and white at the tailhead do not appear to be exclusive to the rabicano pattern. There is overlap between the characteristics of the two patterns.  We can assume that because were all the horses with roaning on the flanks and white tailheads carrying two separate genes, one for rabicano and one for sabino, then the two patterns should segregate in a certain percentage of the offspring. That is, in addition to producing sabino-rabicanos, they should also have some pure sabinos and some pure rabicanos.

Consider the well-known frame overo Saddlebred, Beau Decision. He has a very typical expression of the frame and the sabino pattern together. Not surprisingly, those two genes segregate in some of his offspring.  Here are a few of the sabinos, and here is a pure frame. Another frame, though probably not the only pattern, is here.  (Beau Decision sadly passed away last year.)

That is why many of the horses being called sabino-rabicano probably aren’t carrying two separate patterns; the two patterns are not segregating in the offspring. They should, if the horse really has two separate pattern genes, especially when crossed with non-sabino mates. That would suggest that in some cases, the roaning and the coon tails are part of the sabino pattern. Sabino can mimic them, just as it did with the white sclera in the previous post.

She did not have any noticeable white on her tailhead.  But this sabino roan does, completely with the banding. (For those familiar with Paint Horse bloodlines, this particular horse had the kind of sabino roan-splash pattern often seen in the Sullivans Heathen horses.)

This horse had an almost entirely white tail, and white at the tailhead that looked more like specks than individual hairs. (Unfortunately I did not get any good close-us of it.)

This is the same mare from the side.

All of these horses have the kinds of patterns that are routinely described as sabino-rabicano, and yet these same types of patterns occur in breeding groups where the two traits – flank roaning and coon tails – are almost invariably found together with sabino-type markings.  Given how common the traits are, one would expect it to be easier to find true, pure rabicanos. That is, if rabicano causes flank roaning and white tailheads, but not leg or face markings, why are horses like this relatively rare? And why aren’t horses like these producing them?

I suspect it is because those traits are not exclusive to rabicano, and that the pattern is being over-identified.

One of the most frequent questions I get asked about the breed color charts is why so many horses have rabicano listed as “not determined”. That is because sabino is believed to mimic those two traits, so the only way to be sure the horse has rabicano is to see a horse with flank roaning and a white tailhead without white markings – or at the very least without obvious sabino markings. Those are harder to find than one might think!

By lkathman

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