Tag Archives | genetic testing

An important correction

CarrouselRoi1662 copy
Louis XIV as the Roman Emperor in the Carrousel du Roi, by Israel Silvestre the Younger, c.1662. The depiction of his mount, and a similar one for the Duke d’Anguein, suggest that the silver dilution might once have been present in the Spanish horse population. 

A few years ago, I reported that a Pura Raza Espanola (PRE) mare has tested positive for silver. This was significant since a previous case of what appeared to be a bay silver stallion had been called into question, regarding both a reported test and registration status. Unlike the stallion, the mare in question was not visibly silver – she was chestnut – but was said to be a carrier. Unfortunately, she has since proven to be negative for the dilution. It appears that while the owners used standard testing notation, what they were doing was what the dog geneticist, Sheila Schmutz, refers to as “guessotyping“. More often when people guess the color of a horse, they use the name of the color. This is especially true when a new and interesting color with an appealing name (champagne, pearl) comes to light. Most of the time there are other clues that the owner is guessing, though that was not true with this particular case, where the particulars were a little unusual.  With the proliferation of websites and forums dedicated to the discussion of horse color, and the more widespread use of testing notations in the descriptions of horses,  this is likely to be an increasingly common problem going forward.

From the standpoint of this blog, I have tried to keep a balance between verifying information and being unnecessarily antagonistic with owners and breeders. In the past, owners of horses with unexpected colors or test results have encountered very aggressive – and at times outright rude – questioning from color enthusiasts. What is often lost in these exchanges is an awareness that breeders do not owe enthusiasts copies of test results. Certainly a potential buyer, or a mare owner interested in breeding to a stallion, have every right to ask to see results if the true color of a horse is in question. But what we are often asking is that someone satisfy our curiosity. Owners and breeders are a valuable resource for anyone interested in horse color. Unlike the situation with the model animal for coat color, the mouse, it is not feasible to breed large, expensive animals as part of a research program. Breeders are doing the work, and paying the bills, for that. What’s more, they are in a unique position to observe nuances of color that people less directly involved with the individual animals might miss. Maintaining a positive atmosphere encourages an open exchange of information, and reduces the chance that someone with a unique horse feels burned by the research community.

That said, it is clear that testing notations cannot be assumed to represent an actual test. As much as it would be a good idea if people did not use them without test results in hand, because they are more widely understood than in the past, the temptation to use them as shorthand for a guessotype is there.

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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 (rjude-consulting@hotmail.com) 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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The W20 Project


I mentioned in the last post that the known White-spotting (W) mutations tended to fall into three basic categories, at least in terms of appearance: white, sabino, and white markings. At the moment, there is only one mutation in that last category, known as W20. The paper that documented the pattern, published just last year, had this to say about it:

We previously discovered a missense variant… but did not immediately recognize its functional role… With sequence and phenotype data of more than 200 horses, we now realized that this variant actually appears to have a subtle effect on pigmentation and consequently termed it W20. This variant is common and segregates in many horse breeds.

The paper goes on to explain that of the 145 horses tested, 52 had the W20 allele. According to the supplementary material, the breeds where it was found included:

German Riding Pony
German Warmblood
Gypsy Horse
Old Tori
Quarter Horse
Paint Horse
Paso Peruano
South German Draft
Welsh Pony

That is an impressively broad range of breeds. Along with the Thoroughbred and warmblood breeds, there is a mountain and moorland pony (Welsh), a number of drafts including one of the older ones (Noriker), a colonial Spanish breed (Paso Peruano), and even the Marwari. Taking that into account, and then looking at the known examples of W20, it is tempting to wonder if this might in fact be the mutation most often responsible for the common “flashy white” type of sabino. Those are the sabinos with blazes, stockings and perhaps some white on the belly. It is also the type of pattern thought to amplify the white in other patterns, producing what is sometimes called “sabino boost”.


When the Sabino1 test became available, there was some disappointment that most horses thought of as sabino tested negative. Unlike the Splashed White patterns, which have one common and widespread mutation (SW1), there has not yet been a widespread testable form of sabino patterning. Looking at the list of breeds above, it does seem that if W20 is not the “flashy white” sabino gene, it is at least one of them. If that is the case, garden variety sabinos like the Shire at the top of this post, or the Paint Horse above and Arabian below, might carry it.


There are still a lot of questions about W20. The original paper describes horses with the mutation as having “extended white markings”. From photographs of the known individuals with the mutation, it appears that homozygous W20 horses are more likely to have belly spots, but perhaps not much more than that. That does fit with what is known about breeding programs that center around horses with flashy white markings, and the relative rarity of loudly marked individuals in those lines. It is also clear that W20 interacts with at least one other White-spotting pattern (W5) to produce an all-white horse. What is not known is what it does with other patterns, both other White-spotting variants and unrelated white patterns. If the mutation is present in the Clydesdale, for instance, then what makes white-born foals so rare there? Does it play a role in horses with more extensive patterning or roaning? What is the maximum (and minimum) expression for W20, both when heterozygous and when homozygous?

Shew of Gold GF (W5) with her white foal Supernatural (W5 and W20)

These kinds of questions are important. For breeders, a better understanding of the way these patterns interact would make it easier to produce the “blaze and white socks” image that many find appealing, without getting excessive white on the body. Likewise a breeder of pintos might need to know how to ensure that enough white fell on the body to obtain regular papers.

That is why I am encouraging anyone interested in pinto patterning to participate in the W20 Project. The project is to raise funds as well as collect samples for a more comprehensive study of the W20 mutation. To participate, owners pay $38 – a fee lower than most commercial tests – and submit 2 samples (30 hairs each) for each horse they want tested. Participants will also need to send three pictures (both sides and a head shot showing any markings) and a copy of the horse’s pedigree. Horses with white patterning as well as those without are wanted. Results will be available in June of this year. More information, including information on where to send samples, can be found by clicking the link below, which takes you to the W20 Project page. There is, however, only a brief window for getting involved as all funds and samples must be submitted by April 15, 2014.

Instructions for Participating in the W20 Study

[Thank you, Jackie, for letting me know that the lovely heavy horse at the top of the post was actually a Shire, and not a Clydesdale!]

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