White Line Disease: Identifying, Treating and Preventing

To understand the basics of white line disease, it’s helpful to know a bit about equine anatomy.

• The hoof wall – the outermost surface of the hoof – has three layers.
• The external layer consists of the smooth, shiny covering that most of us think of when we think “hoof.”
• It’s within the next two layers of hoof wall that white line disease usually occurs, making the name a misnomer. The white line lies just inside the hoof wall and is not affected by its eponymous disease.

What is white line disease?

White line disease, or WLD, is characterized by an invasion of bacteria and fungi that destroy hoof-wall tissue. But first, there has to be an opening for these organisms to get in, says Dr. Stephen E. O’Grady, who is both a veterinarian and a farrier. A crack or separation in the hoof wall – which can be caused by mechanical factors such as long toes or a club foot – has to open the way for an opportunistic infection.

White Line Disease vs. Thrush

White line disease shouldn't be confused with thrush. Thrush is a bacterial and fungal infection of the frog. You can spot it by its foul smell and black tar-like discharge, which often ends up on the end of your hoof pick. Learn more about thrush in horse hooves.

What causes white line disease? 

Unfortunately, the cause of white line disease not always that open-and-shut. Many horses have a separation in their hoof wall and do not develop WLD. So it’s hard to say what causes the disease to develop. Wet living conditions may play a role, although WLD can also occur in horses in arid conditions.

• Some kind of hoof capsule distortion will usually be found with WLD, such as a long toe, under-run heels, a club foot or sheared heels.
• A swampy area with excess moisture could soften the foot, and mud and debris could pack into any separations that occur. (Here's how to fix muddy paddocks.)
• A horse in a too-dry environment may experience hoof cracks because of the lack of moisture, and in that case, he’d need moisture added.

Signs of White Line Disease

• Horses can develop WLD in one foot, or in all four.
• Your farrier will usually notice a powdery hoof wall where there should be a solid junction.
• The farrier might also notice a hollow sound when he taps the outside of the hoof wall with a hammer.

Is white line disease painful? What does WLD do?

In milder forms, WLD does not cause lameness or any outward signs. But the infection can progress upward, climbing from the bottom surface of the hoof toward the coronary band. As more of the hoof wall is damaged, the laminae that attach the coffin bone may also be compromised, allowing the bone to sink or rotate, causing a painful laminitis.

If a horse with WLD, or even hoof-wall separation, shows lameness, that’s when a veterinarian should be called in, Dr. O’Grady says. X-rays can divulge how serious the problem is and will help in formulating a treatment protocol.

How to Treat White Line Disease

White line disease can be cured. Here's how a farrier does it.

• First off, abnormalities in the hoof need to be addressed.
• The mainstay of white line disease treatment is hoof-wall resection, where a skilled farrier cuts away all three layers of the hoof wall to remove the infected material. A hoof knife or Dremel tool can clear out the powdery hoof wall.
• Once the farrier has gotten to healthy tissue, he or she can take a drum sander and smooth up the area under the resection. The hoof will grow out better if it’s a nice, clean, solid area.
• The resection might look dramatic to horse owners, but keep in mind that these are not sensitive tissues, and a resection doesn’t hurt the horse.
• The resected hoof may need to be supported with a special type of shoe, such as a glue-on or bar shoe. When you resect the hoof, the horse needs the continuity restored in the form of a shoe.
• Owners can use a wire brush daily to keep the area clean.
• The horse’s hooves should be kept as dry and clean as possible.
• Every two weeks a farrier – or horse owner, if he or she is confident with a hoof knife – should debride the area with a hoof knife. Clean up any area that isn’t looking good, clearing it down to solid tissue.
• During the debridement, a dye marker such as merthiolate is used to stain the tracts of infected material. That tells the farrier how far to keep carving.
• If you keep the hoof clean and debrided, it should grow back healthy, but don’t let your guard down, because the infection can recycle and even reappear in previously affected horses with strong hoof walls that have no sign of separation.

Growing a New Hoof

If more than one-third of the hoof wall (going from the hair line to ground) is removed in a resection, the horse should be taken out of work, Dr. O’Grady says. With one-third or less of the hoof wall removed, the horse can be worked normally.

How long does it take for a resected hoof to grow back? A horse’s hoof, in the toe area, will completely re-grow from hairline to the ground in 10 to 12 months, Dr. O’Grady says. The quarters (sides) of the hoof will grow out in six to eight months. And the heel will grow out in three or four months. So if, for example, a horse has half the length of his toe resected, it will take five to six months to re-grow. Feeding for healthy hooves can help speed up the process.