Reminder – deadline for W20 samples


I wanted to post a quick reminder that the deadline for having your horse included in the upcoming W20 study is this Tuesday, April 15, 2014. As mentioned in the previous post, the W20 mutation is one of the newly identified White-spotting (W) patterns. The majority of these patterns have been new mutations that originated in specific families of horses within the last few decades. The W20 mutation is different in that it has been found in a number of unrelated breeds (a current list can be found here), which suggests that the pattern is old. That means it may be widespread in the equine population.

Unlike the other patterns in the W series, this one does not put a lot of white on the horse – at least not unless it is paired with another pattern. The exact range of expression is not known, however, nor is it clear how it interacts with some of the other forms of white patterning. To better understand that, one of the research groups in Germany is offering the W20 test for a brief time. The idea is to both collect a range of samples and raise the funds necessary to do the work. (Horses, unfortunately, do not tend to attract third party research grants, so the biggest impediment to progress is lack of funding.)


Dr. Rony Jude, one of the scientists involved in this project, has indicated that the horses submitted need not be pintos, or even have obviously flashy markings. Horses like the two included in this post would be helpful. I have submitted my own Appaloosa mare, who has only a moderate blaze and a white hind pastern. Groups of related horses are also helpful. Other good candidates are horses that have known, tested patterns but that have more white than might be expected.

The (English-language) form needed to have your horse included is located here. Owners in the United States will need to send their samples in now in order to meet the deadline. For those that have not done genetic testing before, collecting samples involves pulling 30 tail hairs (the root bulb must be visible). For this study, each horse needs two samples: two ziplock bags of 30 hairs. I would also recommend sending the materials in a padded envelope – not a package – to avoid delays in customs. The form indicates that you need to submit three photos (both sides and a face shot showing markings) and a pedigree. Pedigrees are useful for finding possible sources for the mutation, but they are not required for inclusion in the study; you can submit unregistered horses. Dr. Jude has also set up a PayPal account ( for participants in the United States, where foreign bank transfers tend to be costly. The necessary photos and the form can also be sent to that address, which is a good idea since we are so close to the deadline.

I hope that Dr. Jude and her team get a good turnout for the study. With luck, W20 could prove to be one of the bigger pieces of the puzzle when it comes to understanding how white markings and white patterns work in horses.


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A heritable form of brindle discovered in horses

Figure 1

Most brindle horses are chimeras, formed when fraternal twins fuse early in development. As the fused fetus develops, the pigment of the two individuals migrate along the Lines of Blashko. If the two individuals were destined to have different colors, then those lines take on the two-toned pattern associated with brindle. The results can be very striking, but because the color comes from an accident of development rather than the DNA itself, chimeric brindles cannot reproduce their color.

Breeders interested in brindle have long sought a true-breeding brindle. This past winter, the first heritable form of brindling was identified in a single family of horses. Incontinentia Pigmenti (IP) causes areas of darker pigmentation that follow the Lines of Blaschko, producing a pattern much like that of the chimeras. The mutation is dominant and sex-linked, so all the living examples are female descendants of the founder. Females that inherit the mutation are born brindle, while the males die in utero.

Unfortunately while Incontinentia Pigmenti (IP) is heritable, it is not something any breeder would actually want. A close look at the mare above shows that the affected horses have areas of hairlessness as well as hypopigmentation. The disease – and that is what this is – causes lesions in the skin, and sometimes the hair does not return after the area heals. A comparable disease in human beings causes problems with teeth, nails and eyes. According to the researchers, the affected mares also had abnormalities of the teeth, hooves and eyes. Obviously this is not the hoped-for true breeding brindle.

So like the recently identified Lavender Foal Syndrome, this is not really something that would be classified as a color. It is a genetic disease where the altered color is one of the symptoms. Breeders looking for a genetic form of brindling will have to continue looking.

The above photo is of a third-generation mare from this line, taken from the original paper. That paper is available by open access at PLOS One. The breed of the test family was not given.

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A teaser image from the book


I have been working this past week to finalize the photos for the upcoming book, Equine Tapestry: An Introduction to Colors and Patterns, and I thought it would fun to share a teaser image. The above picture shows how the dappling pattern – including the distinctive ‘spider vein’ pattern on the gaskin – on a champagne is a near-perfect reverse of the dappling pattern on a sooty palomino. I met this mare at a local Appaloosa show, and took numerous photos of her striking coloring.

The reversed veins are visible here on her forearms as well as her gaskins

I have been very fortunate that so many people from around the world have been willing to share images of their horses. Looking through the draft of the book, it pleases me to see so many different breeds, and so many different countries, represented. Three years ago, when I began work on the previous book, one of my biggest worries was whether or not I would be able to get the photos I needed to tell the stories of those breeds. This time around, my biggest challenge is fitting in all the images I would like to use!

Because there are still quite a few steps to go before the book is finalized, I do not yet have a publication date. If there is one thing that I learned from the last time, it is that there are always new ways for a book to be delayed! I will keep blog readers posted as things progress, though.


I plan to post a few more teaser images as I get time in the upcoming weeks, including some additional photos of Vasco Piskui, the manchado Polo Pony from the cover. I was recently contacted by his current owner with some additional images of him that show more of this rare pattern. So keep checking back – or better yet, enter your address to the right (“Subscribe to blog via email”) and have the blog posts delivered to your inbox.

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