Description

White line disease, also addressed as a condition rather than a disease by some veterinarians, is caused by an infection resulting from bacteria, yeast, or fungus that causes the loss of horn at the juncture between the laminae and the inner hoof wall in the horse's hoof.

As the horn disintegrates, it creates a hollow space or cavity that contains a mealy or "seedy" substance. As the breakdown continues, the mechanical loss of the attachment between the laminae and the inner hoof wall may result in displacement of the coffin bone, at which point the horse begins to show discomfort and may become lame.

Often in cases of white line disease, the only noticeable change on the surface of the foot is a small powdery area located near the hoof wall/sole junction. White line disease is most commonly noted as an unexpected hoof wall separation discovered by the farrier during routine hoof care.

White line disease may show up in only one foot or in all four. It begins with a separation that occurs between the wall of the hoof and the sole and it may happen in either the toe area, the quarter of the foot, or the heel.

The breakdown occurs in the part of the hoof that is meant to protect the foot, opening the door to bacteria and fungi which are found in every environment. Once the white line has been damaged, these pathogens enter and deterioration of the inner wall of the hoof occurs.

Symptoms

• A small powdery area along the hoof wall/sole junction usually noticed by the farrier
• Tender soles when checked with hoof testers
• Warmth in the foot
• Slowed hoof wall growth
• Bulge above affected area at the coronary band
• Discomfort when horse puts weight on hoof

Causes

White line disease seldom occurs in horses that are unshod and on pasture. Instead, it occurs most often in horses that are shod, given limited daily exercise, kept in damp stalls, and are exposed to frequent wet-to-dry situations, such as walks in wet grass.

When the bacteria, yeast, or fungus invades the hoof wall, the infection begins at ground level and works its way up the white line to the coronary band.

Excessive toe length, poor hoof conformation, clubfoot, and damage to the hoof wall may be contributing factors.

Vascular damage associated with chronic laminitis, and trauma from a localized blow to the hoof causing vascular damage will also lead to separation of sole and hoof wall leading to possible abscesses and other infections that result in white line disease.

Prevention

Prevention of seedy toe is difficult because the exact cause is unknown, although providing a dry environment for the horse's feet is considered important by many veterinarians and farriers. 

In addition, having a farrier examine each foot when the horse is shod is important. Small, abnormal areas where the sole/wall junction occurs should be carefully examined and debrided down to solid horn. The cavity can be filled with medicated putty before the shoe is attached. Proper trimming and shoeing offers some protection.

Monitoring horses that have previously had the disease is important because white line disease may suddenly reappear.

Treatment

Correcting the primary cause of the hoof wall separation is the first step in treatment. Any hoof capsule distortion that may contribute to hoof-wall separation needs to be corrected. If necessary, the hoof capsule that overlays the affected area needs to be resectioned. Supporting the foot with therapeutic shoeing is important if the hoof wall is extensively damaged.

In some cases, removal of the outer hoof wall to expose the diseased area may be necessary. Debridement of the infected areas should take place over a period of time. The resectioned area should be cleaned daily.

If lameness is present, a thorough lameness examination should be performed to localize the suspected area. Radiology is a useful tool  in assessing the condition. With extensive hoof-wall damage, white line disease accompanied by pain can mimic laminitis both clinically and radiographically, so careful analysis is necessary for a successful diagnosis.

A change in the horse's environment may be necessary. The feet should be kept as dry as possible, with clean, dry bedding and without turnouts in rainy or wet weather.

A well-balanced diet with the addition of biotin and methionine can be helpful. The shoeing schedule should be maintained at four week intervals until all signs of the disease have been eliminated and the hoof wall grows out. The veterinarian or farrier can give advice on exercise and work schedules depending on the condition of the horse.