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The old saying goes, “No hoof, no horse” and truer words have never been spoken. Any horse owner knows that trouble starts from the bottom up and hoof issues can put you on the sidelines for far too long. This is a problem that one of my clients is facing. Her horse is suffering from White Line Disease (WLD) in all four feet and while her farrier and local veterinarian are doing exactly the right things to get her back in the saddle, as a graduate of both the Beginner and Advanced Equine Education Courses she has a thirst for knowledge and asked me for a little more information on the process. And I thought I would share my answer with all of you.     White line disease is a problem of the equine hoof that is seen throughout the world and is still poorly understood by the veterinary and farrier community.  It is characterized by the separation of the inner zone of the hoof wall. This separation that occurs on the solar surface of the hoof can begin at the toe (which is where the old layman’s term “seedy toe” comes from) or the quarter or the heel. The area of separation is then invaded by bacteria and fungus from the environment (remember the separation starts on the bottom of the hoof, which spends most of its time in the dirt). The separation, and infection, can progress proximally up the hoof wall towards the coronary band. Interestingly, the coronary band never becomes infected, which is why the term onychomycosis (a nail bed infection in humans or dogs) is inappropriate to use when describing WLD.

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In vet school I was lucky enough to learn equine orthopedics from Dr. Dean Richardson, the surgeon who cared for Barbaro, and if there is one thing every Penn Vet grad remembers about equine orthopedics, its that you have to know your ANATOMY, ANATOMY, ANATOMY! (though all capital letters cannot truly convey the emotion, or volume, with which DWR screamed this during lectures).
So to understand WLD better, lets review the ANATOMY of the hoof as it pertains to this problem. The Solar Surface of the Hoof     The hoof wall consists of three layers; the stratum tectorium (external layer), the stratum medium (the middle layer), and the stratum lamellatum (the inner layer). The stratum tectorium is the thin layer of cells that give the wall its smooth shiny appearance. The stratum medium forms the bulk of the wall and is the densest part of the hoof wall. The stratum lamellatum arises from the laminae, is nonpigmented, and is responsible for attaching the hoof wall to the third phalanx, and is what gives us so much trouble in cases of laminitis or founder. The junction where the sole attaches to the wall of the hoof is formed by interdigitation of lamellae and horny tubular tissue. This is the area known as the White Line, though in real life it is often yellow in color.

So how does separation occur between the sole and the hoof wall? And the question most owners ask, “Why is this happening to my horse?” While there are a lot of theories out there about what causes WLD, none of them have been confirmed. It can affect horses of any age, sex or breed. It can affect one foot or a combination of all four. Horses with shoes get WLD and barefoot horses get WLD. Horses in every country can be affected and you may have one case on a farm or multiple ones. Mechanical stresses that are constantly being put on the hoof can contribute to the separation and chronic hoof problems and poor conformation may also be a cause.     Some people believe that moisture plays a role because, just like Scratches, it is so often seen in horses that spend time in wet paddocks or show horses who are bathed daily. However, it is also seen in arid climates. Moisture may soften the foot, allowing easier access for bacteria and debris, but hot, dry conditions make hooves prone to cracking, allowing the microbes to invade. And don’t try to blame the housekeeper, because WLD is seen equally in areas of poor hygiene as well as clean, well-managed stables.
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Not all horses that have WLD will become lame. It is often an incidental finding at a routine farrier appointment. However when the separation becomes so extensive that there is destabilization of the whole hoof, horses will become sore. The diagnosis is made by your vet or farrier examining the hoof and investigating if there is a gap between the hoof wall and the inner structures. Radiographs (x-rays) can be very helpful because they show the extent of the damage and if there are any other structural problems with the hoof or the coffin bone.

Treatment involves opening up the spaces by removing the overlying hoof wall (with a dremel tool). Once every cavity is exposed, topical antiseptics can be used judiciously (no more than once or twice a week) to clear up the infection. Afterwards corrective shoeing will help support the hoof while it regrows the resected portions. Acrylic can be applied to the area to prevent recontamination, or for cosmetics, but should only be used once the infection is completely resolved. 

    Because we don’t know the exact cause, it’s difficult to make recommendations on how to prevent WLD. But daily hoof care on your part and proper trimming and shoeing performed by a well-trained farrier is the first step to recognizing a problem early on. Horses that have had WLD should be monitored all the more closely as the can have spontaneous recurrence of the disease.

            So keep your eyes open and your horse’s feet well cared for and you can stay on the trail or in the ring without problems!
 

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