Opening a can of worms

blazedtobiano2

I intended to post another example of reverse dapple roaning, but an interesting development in an obscure pony breed – and an unrelated discussion on an online forum – convinced me it was probably time to air this topic.

For some time I have flirted with an idea that is quite simply heretical in horse color circles. Something so far out there, that only the most uniformed horseman might entertain such a notion. But evidence is evidence. If the evidence does not fit universally held beliefs, then it is time to examine those beliefs even if it does give some people heartburn.

So what is so beyond the pale in the horse color world? What have some researchers noticed, but feared to mention?

The tobiano pattern is sometimes associated with white markings on the face. 

There. I have said it. I have noticed it for some time, as have others that were looking at some of the same breeds, or closely related breeds.

This was not something I was looking to find. What I was looking for was clues that some of the old Nordic or Celtic pony breeds still had splashed white. Most of these are breeds that either did not originally have “ordinary” markings, or where white markings – but not pinto patterns – were systematically bred out of the population. Quite a few of those breeds have classic splashed white (SW1), so it was reasonable to suspect that the horses with white on the face were heterozygotes (Sw1/n). Furthermore, it seemed likely that such a pattern could “hide” in the tobiano populations of the breeds where that was allowed, since few people minded if there were markings on a horse that already had a pinto pattern. The problem was that the expected SW1/SW1 homozygotes – the splashes with the classic pattern – never seemed to materialize. What’s more, when these ponies were crossed on solid mates, the face markings rarely appeared unless the tobiano pattern was also there. Even more tantalizing to someone looking for splash, these same ponies threw occasional blue eyes as well as the face white and the tobiano pattern. (I guess that counts as my second heresy in one post…)

I should clarify that I was looking at pretty unusual breeds. In the United States, it is quite difficult to find a popular breed without white markings of some kind. Most New World breeds not only have white markings, but many have what could be called sabino markings. In these breeds, like the Paint Horse pictured at the top, it is quite reasonable to assume that sabino (or splash or frame) are involved when a tobiano has a lot of white on the face. The question really is whether it is possible to get white on the face of a tobiano without these, or without the basic genes for white markings.

And now that question is being asked quite openly in a controversy surrounding the ancient Hucul Pony.

huculy-gladyszow1

The Hucul is a primitive pony breed from the Carpathian Mountains. Most are dun, but tobiano is also a traditional color within the breed. Earlier this year, the parent stud book in Poland proposed separating out the tobiano Hucul population into a separate stud book. The reason? Because the tobiano ponies often have white on the face. It was feared that with the growing popularity of the tobiano pattern, the solids were in danger of having markings.

[Polish and Hungarian officials] claimed that piebald Huzuls transmit markings in a greater extent and these markings were undesired. Both recommend that piebald stallions may not cover plain mares. It is proposed to administrate piebald Huzul horses in a separate studbook.

There has been an outcry among breeders of tobiano Hucul Ponies that this fear is baseless because the leg markings on a tobiano are part of the pattern, which is permitted. The face markings, it has been noted, do not seem to pass along to the solids. This has lead to a discussion about the connection between face markings (and blue eyes) and the tobiano pattern. Some of the excerpts from this discussion are interesting:

This is from the paper “Odmiany a srokatosc” (Markings and Piebald) by Anna Stachurska. The emphasis is mine.

Piebald Huzuls have the Tobiano gene, plain coloured Huzuls have not, even if they have piebald parents. Piebald Huzuls may have more markings because the Tobiano gene is located near one important gene for markings and the properties of genes in neighbourhood usually show up together. But this does not matter as piebald Huzuls have white spots anyway. In plain coloured Huzuls, even if they have piebald parents, an absent Tobiano gen cannot influence the appearence of a gene for markings. This means that plain coloured Huzuls with piebald parents need not to have more markings than Huzuls at all.

In clarifying her paper, she also writes this.

I would not write that tobianos have non-piebald head. In American publications tobianos are described as “conservatively” marked on the head or “with minimal extent of markings” on the head. However, in Poland tobiano halfbred horses (e.g. Wielkopolski, Małopolski) have rather big markings on the head, even with a glass-eye, though the markings are not bigger than “normal” (usual).

There has been some research on the subject of markings in recent years, notably one of the Franches-Montagne. From these discussions, it appears that there is more research being done. It is certainly too early at this point to say why tobianos in otherwise solid, unmarked breeds have a higher incidence of white on the face, but it does look like the subject has attracted some attention. Resolving the conflict between the different Hucul stud books may help provide some incentive to research this situation in more detail.

(Huzul group picture from Wikimedia Commons.)

, ,

19 Responses to Opening a can of worms

  1. Kristin Berkery September 5, 2012 at 9:15 pm #

    Omigosh my head is swimming… I need to process this info for awhile!

  2. Joanne Abramson September 5, 2012 at 9:41 pm #

    There are so many different types of “blue eyes”. From dark blue to light sky blue. The darker blue eyes seem to be associated with horses that appear and test positive for tobiano; and do not test positive for LWO, Splash, or Sabino. Tobiano plus another pinto gene are more likely to have medium blue eyes or a single blue / brown eye. The lightest blue eyes are associated with the dilution gene and seen on cremellos, palominos, etc. I am curious which “Blue” color these tobiano horses have?

    • The Equine Tapestry September 7, 2012 at 4:39 am #

      Unfortunately the ones that I have seen have not been in person. I find eye color to be one of those things where shade is much more reliable if you can see the actual horse.

  3. Marika September 6, 2012 at 4:11 am #

    Yay, for Nordic breeds!
    I’ve seen plenty of tobiano Iceladics with white marking(s) on their face, mostly in a form of a star and/or snip. Couple blazes as well, but those horses are usually mostly white, like the horse shown on this post and some even more white. So I have been wondering if they had a splash gene as well, since sabino is something they don’t have. So I’ve always believed that tobianos with head markings were normal, until someone told me tobianos usually don’t have head markings…

  4. Shanti September 6, 2012 at 7:46 am #

    I’m in love with that pretty tobiano!! Do you have a picture of his other side too? Maybe? Please? ;-))

    • The Equine Tapestry September 7, 2012 at 4:42 am #

      I have a lot of pictures of both sides, since he was being set up in the one part of the horse park that has really good lighting. I will be away for a week in Boise, but I will post more when I return.

      • Shanti September 7, 2012 at 1:13 pm #

        Great, thank you!! :)

  5. Keren Gilfoyle September 6, 2012 at 8:12 am #

    Given that tobianos in the UK almost invariably have white face markings, I’ve always been nonplussed by US researchers insistence that tobiano *doesn’t* cause white on the face….

  6. Gael O'Brien September 6, 2012 at 8:47 pm #

    The tobiano in the top picture obviously has splash as well. I think the problem isn’t that tobiano causes white markings, but other white patterns that happen with tobiano are not correctly identified.

    • The Equine Tapestry September 7, 2012 at 5:08 am #

      Yes, the horse in the picture is an American Paint Horse and is almost certainly carrying another pattern in addition to tobiano. I did not get his name, so I cannot look up his pedigree to see what those other pattern possibilities might be. (I am pretty conservative when it comes to labeling face markings as “obvious” when it comes to pattern, though.)

      He is not an example of a suspected pure tobiano, though. He is an example of why the situation is muddied if what you are looking at are tobianos in breeds that have both ordinary markings and other white patterns like sabino. In the United States, that’s pretty much true of most tobianos. But there are a few breeding populations – primarily primitive pony breeds – where ordinary markings are absent (or in some cases, really rare). It is the situation regarding face markings on tobianos in those breeds that has raised the questions.

      I would also add that the people who have noted this, myself included, were all researching the splashed pattern (SW1). Obviously anyone can incorrectly identify a pattern, especially when there are still so many patterns without actual tests. But in each case, the research lead to independent conclusions that SW1 was incompletely dominant, which is now supported by test results. We each also noted this situation with the tobianos. Like I said in the post, this was not a theory I held at the start (“tobianos sometimes have white on the face”), but a theory that came up short (“these tobianos with white on the face are splashes).

  7. dakota328 September 7, 2012 at 8:29 pm #

    It is interesting, the 3 Tobianos (all paint crosses) at the barn I board at all have face markings: A large star, a blaze and a wide snip type thing. I assumed some sort of Sabino for each of them, perhaps it is just because of Tobiano itself.

  8. Threnody September 8, 2012 at 1:59 am #

    I think there is also a chance of some lines of tobiano having mutations of sabino or other KIT cause facial markings linked together. That way tobiano and the face markings would pass on together nearly every time. Especially since KIT is so notorious for pattern mutations.

  9. accphotography (Audrey Crosby McLellan) September 11, 2012 at 7:10 pm #

    I just wanted to say I agree with this. Researchers have been saying it for years but die harders have refused to believe it. I was a die harder at one time but over the last couple of years have really come to believe it does happen. According to the researcher who found the tobiano inversion it does cause face white (and she even says blue eyes, but this was prior to splash test availability) and the white (and eyes) appears to be more significant in homozygotes.

    • The Equine Tapestry September 21, 2012 at 7:13 am #

      That is certainly consistent with what I have observed in homozygous tobianos.

    • Joanne Abramson September 21, 2012 at 9:57 am #

      We have a number of blue eyed homozygous tobianos that have tested negative for the other pinto genes. They may have a gene we cannot test for at this time, or we will have to conclude that tobianos can have facial white and / or blue eyes.

  10. Caitlin September 24, 2012 at 1:31 pm #

    I’m not sure that I buy it. The Polish writer is suggesting that in the Huzul pony, there is a chunk of DNA in the genepool that has both the tobiano inversion of KIT PLUS a SNP (presumably) permitting white markings, and that due to their proximity on the chromosome (both involving KIT!), they are passed on together or not at all. I would suggest that it is very likely that due to the proximity of the tobiano inversion of KIT and the KIT gene itself, there would be families that were known for tobiano + white markings and families known for tobiano – white markings. This “gene linkage” is very basic genetics, and has been taught in high school biology classes for more than 15 years. So in the case of the Huzul pony, I would say that tobiano and white markings are associated with each other, not that tobiano is overtly causing the white markings.

    For that matter, I don’t buy that “the gene” for white markings is some single, identifiable recessive allele. The migration of melanoblasts is a complex process; there are many ways to delay it enough to cause white markings. I expect that we will learn that any number of small SNPs of KIT and other related genes can cause white markings alone or in concert with one another. That latter point would account for an apparently “recessive” mode of inheritance.

    • The Equine Tapestry September 27, 2012 at 7:15 am #

      The papers that I have read on markings do not seem to assert that it is a single gene, but do suggest that there is a large effect gene as well as small effect genes involved. I would be very interested to hear your take on the Franches-Montagne paper, since it is the most current on that topic.

      And I would love for someone to do the research to see if what myself and others have observed with some tobianos is due to linkage or tobiano itself. As much as I might like to know which it is, for the purposes of most breeders, if that linkage is strong then the end result is the same no matter the molecular cause: tobianos may or may not have white on the face, and that white is unlikely to appear on their solid offspring. It also would mean that automatically assuming white on the face of a tobiano means another pattern (sabino, frame or splash) is present would be mistaken. I know that molecular findings often have broader implications, but that is the practical application for horse people.

      • Caitlin November 15, 2012 at 9:26 am #

        Let me pose the tobiano question this way. Which follows?
        a. Some horses with tobiano have white face markings, therefore white face markings are a characteristic of tobiano, or…
        b. Some horses with tobiano do not have white face markings, therefore white face markings are not a characteristic of tobiano.

        I agree that the practical applications for horse people often differ from what we’d just like to know because we’re curious. However, in this case, the important take-away for the breeder is that in individual horses, the presence or absence of white face markings (and the presence or absence of black in the coat, for that matter!) and the tobiano pattern are linked, but that linkage is important on an INDIVIDUAL basis and one cannot extrapolate outside of the individual or at least his family. For example, if we have a black heterozygous tobiano with a recessive red allele at the extension locus, it is important for breeders to know whether his tobiano allele is on the same chromosome as the red allele or the non-red allele. We can look to Art Deco in this case, whose tobiano allele was on the same chromosome as his dominant non-red allele, and thus sired black-based tobianos and solid chestnuts, and only one or two chestnut tobianos, who had tobiano mothers.

        As far as studies of the Franches Montagnes horses with white-causing KIT mutations goes. My take on “Haematological parameters are normal in dominant white Franches–Montagnes horses carrying a KIT mutation” is that this is important information, and I’m glad they studied it. It does not mean that any novel mutation of KIT may be considered “safe”, but it may turn out that horses do not use KIT in the development of their blood cells.

        My take on “Allelic Heterogeneity at the Equine KIT Locus in Dominant White (W) Horses” is that this is also important information, but that because of where genetics education stops in public schools, it is less accessible to the average horse person. This allelic heterogeneity is important in the study and treatment of cystic fibrosis in humans. Actually, I’m sure it’s important in many genetic diseases, but CF is what I think of. Our understanding of how a mutation affects phenotype can only go as far as our understanding of how the body uses the protein that is encoded by the gene. I don’t think I can do the topic justice here, but maybe you can.