White-line disease refers to a condition where the white line crumbles and leaves an empty gap in the white line. However, many horsemen remain confused over what truly constitutes a white-line problem that requires treatment and what factors are involved as causes versus consequences.
Real White-Line Disease
When most people talk about white-line disease they’re referring to an infection in the tissues of the white line that travels up the hoof wall, toward the coronary band. However, the fact the white line appears “empty” at ground surface doesn’t necessarily mean the horse has true white-line disease. When the toe is too long, especially in unshod horses, the white line is stretched each time the horse puts his foot down because the hoof wall will expand somewhat and tug on the white line. This can cause a mechanical separation of the tissues close to ground level.
Horses kept on dry surfaces can also have some crumbling of the white line, and the combination of a too-long toe and dry conditions will likely cause crumbling and loss of the white-line tissue. If gentle probing of the hollowed-out area shows it only extends a short distance up the wall, and trimming the horse correctly reveals a healthy white line, no treatment is necessary.
A hallmark of true white-line disease is that it leaves a hollowed-out area in the hoof wall that extends up into the hoof. It may get its start from the conditions described above, or as a consequence of separations that occur along the white line when a horse has laminitis.
The second ingredient for true white-line disease is an infectious organism. Most cases involve fungus, and a variety of different fungi have been identified. Bacteria may also be involved, or a combination of the two. The path of the infection through the damaged white line can be seen as multiple small black tracts.
Keeping horses under dirty conditions (manure, urine) is never good for hoof health, but there’s no evidence just muddy ground conditions are any more of a risk factor for white-line disease than dry ground/dirt.
Successful treatment begins with identifying the factors that led to weakening of the white-line tissues in the first place. Trimming is the first step. Dr. Steven O’Grady, Northern Virginia editor of Equine Podiatry, recommends the removal of the hoof wall overlying all hollowed out areas, with the resection taken high enough to locate and expose the junction of dead, infected tissue with healthy white line. All the exposed diseased tissue is then removed. Resections should be down to the level of diseased tissue only, never into healthy tissue, which means no pain and no blood.
Simply exposing the area to sun, air and light is important. The application of methiolate, gentian violet or a weak iodine solution can be done as mild antiseptics and to help stain any infected tracts so that they can be easily seen. However, strong solutions of phenol, iodine or other chemicals should be avoided. O’Grady reports treating severe infections of the coffin bone in horses that have had these chemicals applied.
The mild disinfectants/dyes can be applied twice a week and will help identify any tracks that need further debridement. The resected areas will harden within a few days and can be kept clean by daily brushing with a wire brush.
If the resected portion of the hoof is small, the horse can be shod as normal, with care being taken to place the front of the shoe back at the correct anatomical position for breakover. When resections are more extensive, the horse may benefit from use of an egg-bar or heart-bar shoe.