White Line Disease of the hoof.

Hoof Disease Threat Grows
By: Stephen E. O'Grady, D.V.M.

Farriers and veterinarians are noticing a growing problem in horses' hooves called White Line Disease. It appears to be more prevalent in hot, humid areas but has been occurring in all parts of the United States with increasing frequency. It doesn't seem to be an issue of poor hygiene, as the problem is seen in well-managed stables. Yet it's difficult to prevent because veterinarians and farriers are unsure of its cause.

Just what is White Line Disease? Simply put, it is deterioration of the inner part of the hoof wall. The "white line" refers to the distinct non-pigmented inner layer of the hoof wall. On the ground surface of the foot, it lies next to where the hoof wall joins the sole.

In the disease's early stages, the only noticeable change on the ground surface of the foot is a small powdery area located along the hoof wall/sole junction. This may remain localized, or it may progress to a larger area of the hoof wall.

White Line Disease may be found in one foot or all four and is found among all breeds of horses. It begins with a separation between the hoof wall and the sole. This can occur in several places-the toe area, the toe and quarter of the foot, or the heel. This separation removes the protective part of the hoof wall/sole junction and allows bacteria and fungi-pathogens readily found in the environment-to enter. These organisms mayalso gain entry through cracks in the feet, nail holes or fissures at the white line.

The destructive effects of these pathogens lead to progressive deterioration of the inner hoof wall.

The term is also used to describe seedy toe in its early stages-a small, circular powdery area in the hoof wall at the center of the toe in many horses.

Factors contributing to separation at the hoof wall/sole junction are excessive moisture; unbalanced feet; improper trimming, an acute hoof angle such as that seen with long toe-under run conformation; flexure deformities (contracted tendons); clubfoot and concurrent hoof problems such as hoof cracks; chronic infection (abscesses or gravel); or direct trauma with subsequent bleeding.

White Line Disease can also occur secondarily to chronic laminitis where the laminae and associated hoof wall are compromised.

White Line Disease poses no threat to the animal's soundness until extensive damage is done. The horse will only appear lame after the disease has caused the laminae and the hoof wall to separate, resulting in the rotation of the coffin bone.

Early warning signs of the disease may be tender soles as seen with hoof testers; occasional heat; the sole becoming flat; a dish forming along one side of the hoof, with a bulge on the opposite side directly above the affected area; slow hoof wall growth; poor consistency of hoof wall; and a hollow sound when the outer hoof wall is tapped with a hammer. On the ground surface of the foot, the white line becomes wider and softer and has a chalky texture.

In the early stages, keen observation by your farrier is necessary to detect subtle changes in the ground surface of the foot. More often, the disease goes undetected until the horse begins to show discomfort. At this point, the affected area can be readily found on examination of the foot, and the extent of the hoof wall loss can be determined with X-rays. With extensive hoof wall damage, the painful stage can mimic laminitis both clinically and in x-rays.

Treatment of White Line Disease is directed at the affected area of the foot and supporting the foot with therapeutic shoeing if hoof wall damage is extensive. Regardless of the extent of damage, the affected area must be treated through resection-removal of the outer hoof wall to expose the diseased area-and debridement-removal of damaged tissue.

The exposed area is debrided every two weeks until there is a solid junction between the inner hoof wall and the lamina. At this point, the area can be left to grow out with periodic
debridement, or the defect can be repaired with an acrylic substance.

Alternatively, various medications such as merthiolate, betadine ointment or two percent iodine can be applied to the debrided area. All of these preparations are used to treat infections and have a drying effect. These medications are applied to the affected area, and the area is packed with gauze and held in place with duct tape.

Another method is to use a piece of sheet metal cut and molded to fit over the defect on the outer hoof wall and attached with screws. This keeps the area clean and allows the packing to be changed at regular intervals. Whatever the treatment, it must be combined with thorough debridement.

The type of shoe needed depends on the extent of the damaged hoof wall. If the defect is small, the hoof is balanced and the foot shod normally. If the resection is extensive, a full-support shoe (heart bar or egg bar-heart bar combination) is used. The shoe must allow any diseased area of the hoof wall from the toe to the heels to be resected and treated while providing adequate support. The full-support shoe supports the heel and allows some weight-bearing to be transferred from the hoof wall to the frog.

The extent of the damage determines the amount of time required to treat the disease, as the affected area has to grow out. For example, if the affected area extended up near the coronary band in the toe area, it will take about 10 months for the defect to fully grow out. However, it is not usually necessary for the horse to be out of work this entire time. The amount of exercise permissible while treating White Line Disease depends on the severity of the damage.

Discussing the problem with your farrier and having him examine each foot when the horse is shod is extremely important. Any small abnormal area should be explored and treated. Proper trimming, balancing of the foot and correct shoeing are also vital to maintaining a healthy foot.

Stephen E. O'Grady, D.V.M., operates Northern Virginia Equine
Podiatry Center near Marshall, Va.