A slide show of affected hooves from around the world; these hooves are all on Connemara ponies, although it is not known if this particular type of wall separation is limited to that breed.
Wall separations are commonly seen in the heel area of hooves, but this is different.
At first, it was easy to dismiss the communications as white line disease or just poor hoof maintenance. But they kept coming back. Soon they had amassed evidence of Connemara ponies with this problem from places as far afield as New Zealand, Finland, and Canada.
Robert Eustace of the Laminitis Clinic in England described the problems as "coconut matting hooves". I thought that was an apt description; in some cases, the inner, exposed hoof wall looked like steel wool fibers. Many cases of this type of dorsal hoof wall separation deteriorate to a diagnosis of laminitis.
According to the owners' group, hoof samples of affected Connemara ponies referred to Eustace for treatment were analyzed by the University of Edinburgh, where they found a malfunction of lipid metabolism in the extracellular matrix of the hoof wall between the tubular structures of the hoof wall.
In simple terms: there seems to be a lack of the 'waterproof glue' or 'cement' that holds the hoof wall tubules together, but the findings have not been documented. Nothing about the condition has been documented, other than by horse owners comparing notes.
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| This image from UC Davis shows a ruler used to measure the extent of a separation lesion on a foot from a cadaver. |
They may not have reached the root but they are cracking the case. If you have a pet problem in the hoof world and you are sure that there has to be an answer, let this group of dedicated horse owners give you a model to follow.
This hasn't been easy. On November 11, 2011, I interviewed a regional president and another officer of the American Connemara Pony Society who assured me that they had never heard of the problem and it was surely just a misunderstanding. A veterinarian concurred.
In their defense, this problem is widespread geographically but still relatively uncommon. Since then, owners tell me, the Society has become aware of the problem. It is also possible that owners whose young stock exhibit this problem are not likely to bring them to shows or to comment much about the problem, in the interest of the value of their other horses.
The Connemara owners scattered around the world with lame young horses on their hands eventually found each other, thanks to the Internet. They also found someone who would listen to them. The unraveling of the horse genome has meant that equine disorders that seem to be breed-specific can be examined on the genetic level, so researchers at the Bannasch Laboratory at the University of California at Davis were able to tackle the problem from that angle. (See below for specifics of the genetic assay.)
When a case cropped up near the university and they saw the problem firsthand, they were even more interested.
Is this problem really limited to a single breed? I remember old farrier texts that complained about mice nibbling on the hooves of certain horses at night in the stable--that was a convenient explanation to owners for a problem that looked like the photos you see in the slide show.
A confounding aspect of the problem is that it occurs in radically different environments, without respect to wet or dry, hot or cold, and appears early in the pony's life.
One Connemara owner remarked, "I am seriously starting to think that this issue is probably quite widespread in the general horse population but appears so randomly that it is acknowledged just as 'bad feet with no known cause'. It is only when one has a small inbred population with the over use of certain bloodlines in an already contracted gene pool that the problem becomes more common and obvious.
"Once there is a commercial gene test available, it will be interesting to see whether there is the same or similar problem in other breeds."
Because the cases are farflung, documentation of treatment is sparse. In most cases, some combination or variation of supportive hoof orthotics, foot casts and glue-on shoes along the lines of laminitis treatment are used. Various topical treatments and nutritional supplements have been used. These efforts are under the heading of managing the condition; euthanasia is common.
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| An example of the type of hoof wall undermining labeled "Hoof Wall Separation Syndrome" by the University of California at Davis, where research is continuing into this problem. |
Updated research summary provided by the University of California at Davis School of Veterinary Medicine
Researchers at the Bannasch Laboratory at UC Davis report:
This hoof defect develops in young foals between one to six months of age. The condition results in afflicted ponies having to support weight on the sole of the hoof instead of the dorsal hoof wall.
Affected animals can become severely painful despite careful management; their quality of life can diminish and euthanasia may be necessary. Even if the condition is initially controllable, ponies may still develop laminitis over time.
HWSS is particularly troubling for the Connemara community because the parents of affected ponies are themselves completely unaffected.
Although affected individuals do share common bloodlines, it is problematic to predict whether a particular breeding will produce a foal with unhealthy hooves. Investigation into the underlying genetic cause of HWSS has the potential to inform these breeding decisions, and could also provide insight into the disease pathophysiology.
To investigate the underlying genetic cause of HWSS, a genome-wide association study was performed and a strong association between disease status and polymorphisms in a two-megabase (Mb) region of the genome was observed. Sequencing of candidate genes within this region is currently underway, and any functionally relevant genetic differences identified will be validated using a larger sample set.
Consequently, we are still collecting DNA samples from both affected and unaffected Connemara ponies. If you are interested in submitting a sample, please contact Carly Stevens (cstevens@ucdavis.edu) or Kartika Jayashankar (kjayashankar@ucdavis.edu) for more information.
Funding for this research has been provided by the Morris Animal Foundation, UC Davis Center for Equine Health, and Merial.
Information for this research summary was provided by the Bannasch Laboratory at the University of California at Davis.
Thanks to all the heartbroken Connemara pony owners who faithfully documented their horses' problems and to all the vets and farriers who have tried to help them, even if they couldn't explain the problem. Maybe someday they will.
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| Click on the ad for more information about this anatomy chart that shows the zones and structures affected by HWSS. |
To learn more:
Connemara pony research into hoof wall separation syndrome blog
California case seen by veterinarians at UC Davis
Functional design of horse hoof keratin by Bertram and Gosline
Isolation, characterization and pressure response of equine hoof keratinocytes by Alanna Chaudhry
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| Click to download full details and ordering information. |
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