A friend recently shared a picture of this Clydesdale mare, Olde Tyme I. M. Nina ("Nina"). Her trainer, Jen Hemphill of Rolling Thunder Farm, was kind enough to let me share pictures of her on the blog. White spotting in Clydesdales is a fascinating topic all on its own. Still, I wanted to share Nina because she is such a good illustration of the limits of visual identification. All patterns (and colors, for that matter) have outliers—examples significantly different from what is typical. Often, those outliers overlap what is typical in another pattern.
All Clydesdales are sabino patterned, and modern Clydesdales tend to have a fair bit of white on the body. However, for the breed, this pattern is an outlier in the percentage of the coat that is clear, pink-skin-underneath white. Beyond just the amount of white, what makes Nina's pattern so interesting is just how closely the placement of the white mimics frame overo. When paired with a sabino pattern, frame overo looks like this. Notice how she has a roany band of color down her topline, ending in deeper (less roany) color on her rump. She has color around her eyes and over her ears and poll. And finally, she has a "shield" on her chest and roany "rosettes" on her flanks.
For comparison, here is a Paint Horse with a visually similar pattern.
Frame overo is limited to breeds developed in the Americas. Nina is a registered Clydesdale, so the expectation is that she would test negative for frame overo. There are also a few subtle differences that read as sabino rather than frame, like how the color on her neck extends down further along the sides.
Another difference between Nina's pattern and frame overo is how the white crosses the highest point of her hips, splitting the color on her rump from the color down her back. That's relatively common in extensively white Clydesdales but not in sabino-frame combinations.
This gives a distinctive "spot around the tail" effect visible on Nina's pattern. She is pictured on the left, and the Clydesdale pictured above is on the right.
Outliers are always interesting because they raise questions like "What is boosting the white?" or "What is causing the position of the pattern to shift?" They point toward things science hasn't discovered—or at least where the answers aren't yet complete. There are some exciting developments regarding sabino phenotypes that I plan to look at once I finish the posts on greys. In the meantime, I'll share a few more pictures of Nina because she is a very cool horse. (She's also looking for a new home if someone wants a talented and colorful young mare!)
