White line disease (WLD) 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.

Causes

• 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 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
• WLD is seen equally in areas of poor hygiene as well as clean, well-managed stables

Signs

• A small white/yellow “powdery” area located anywhere along the hoof wall/sole junction
• Horses may become tender on their soles when squeezed with hoof testers and the soles will become flattened
• Occasionally there is heat in the feet
• There will be slow and poor growth of the hoof wall and a hollow sound can be heard when the hoof is tapped with a hammer
• Lameness only occurs when the disease is severe enough to allow detachment between the laminae and the inner hoof wall resulting in rotation of the coffin bone

Diagnosis

The diagnosis is made by a veterinarian 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

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.

Prognosis

With proper treatment WLD can be corrected and the hoof return to normal. Because we don’t know the exact cause, it’s difficult to make recommendations on how to prevent WLD. 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 they can have spontaneous recurrence of the disease.