White Line Disease: An Infection of Opportunity in Equine Hooves

You’re picking your horse’s hoof and notice a spot near his toe where the pick goes a little deeper than it should. There’s also a wee crack on the outside of the hoof. Digging in slightly, you find crumbly, greyish-black, powdery stuff. This all could indicate white line disease, a common infection, which, if left to fester, can create a lot of trouble in the internal structures of the hoof.

The white line is the pale area on the underside of the hoof where the outside wall meets the sole. If damaged, it becomes an entry point for anaerobic (non-oxygen-loving) fungi and bacteria, which get trapped and thrive in the damp, dark inner hoof. Their presence, combined with certain mechanical factors, causes progressive separation of the hoof wall.

“It’s really an infection of opportunity,” said B.C. journeyman farrier Roger Sutcliffe. “But we’re not really 100 per cent sure what creates the opportunity.”

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As Sutcliffe suggests, white line disease, sometimes referred to as seedy toe, is somewhat of a mystery condition. For one thing, experts aren’t clear on exactly what pathogens are involved and how they initiate the biological processes that lead to deterioration of the hoof wall.

“It doesn’t make a lot of sense the way it behaves,” said Sutcliffe, who spent much of his farriery career trimming and shoeing pleasure and show horses in Chilliwack before moving to Ashcroft in the province’s interior a couple of years ago. There, he works mainly on ranch and working horses.

“You can have one foot with a really bad infection and the other three feet will be fine. It can affect horses in dry conditions that get wet for very brief periods of time, like in some parts of the southwest in the desert, they get really bad outbreaks, and you can have horses living in swamps that don’t get it,” he said. “To be quite honest, most of my issues of white line disease are with horses that are very well managed. It’s not in the nasty, stinky barns with horses that have poorly maintained feet. Some of the worst cases I’ve had are with high performance horses that are well kept in good stalls on good nutrition…and why?”

Mechanical stresses contributing to white line disease include poor hoof conformation, hoof neglect, riding on hard surfaces and other trauma, too much weight on a horse and prior conditions such as abscesses and laminitis. Sutcliffe says he has also seen some examples that could be linked to poor nutrition.

White line disease doesn’t, in fact, occur in the white line. It mainly affects the stratum medium, the non-pigmented middle layer that makes up the bulk of the hoof wall. When the hoof experiences unusual mechanical stresses, rocks, dirt, manure and other materials infiltrate the hoof. And they may contain the offending fungi and bacteria, which eat away at the stratum medium. If unthwarted, the pathogens make their way to the stratum internum, the deepest part of the wall, which joins the hoof capsule to the coffin bone.

“The infection doesn’t seem to go in the vascular area where there’s a blood supply, but that means it can literally go all the way up the front of the hoof wall to within a quarter of an inch of the hairline and now you’ve got a very unstable hoof capsule,” Sutcliffe said. At this point, coffin bone rotation can occur.

Other than the dry, crumbly cheese appearance and soft spots, an owner will likely also notice a widening of the white line, and perhaps a hollow sound when they tap on the hoof wall. Chronic cracking on the front of the hoof is another indication of infection, especially “the kind of cracks where it looks like it’s overlapping itself. Sometimes [white line disease] is what’s driving that because there’s no structural attachment,” explained Sutcliffe, who urges owners talk to their farrier about their concerns during the horse’s next trim.

He sees minor cases on a regular basis. “I hesitate to call it full-blown white line disease, but it’s probably a similar process, where you’ve got a little bit at the bottom of the hoof, you clean it out with your farrier knife, there might be a small loop or a notch visible on the outside of the hoof capsule. You discuss with the owners some basic treatment and two shoeings later, it’s gone. That’s probably the most common scenario.”

Sutcliffe is a proponent of early, aggressive treatment for bona fide cases of white line disease with significant infection extending up into the hoof toward the coronary band. “It’s not something you want to ignore. It’s definitely something that needs to be cleaned up and dealt with.”

He says treatment is usually a two-step process beginning with exposing the infected area by removing the hoof wall and then, the most important part, debriding (removing) the diseased material to prevent its spread.

In some cases, it’s necessary to include a veterinarian, especially if treatment involves getting into vascular areas. Sutcliffe’s rule of thumb: “If it’s going to bleed, you need to have a vet involved.” A vet will likely x-ray the hoof to reveal the voids left by the infection and map the potential extent of the disease process. Radiographs can also provide an important reference when monitoring the position of the coffin bone for risk of rotation. After resection and debriding, the farrier, and veterinarian if involved, will assess the stability of the hoof.

“If you remove a large percentage of the hoof, then you’re starting to look at specialty shoes,” said Sutcliffe. Traditionally, this would usually have meant using an egg-bar or heart-bar shoe to stabilize the foot by providing support to the heel and allowing weight to be transferred from the affected hoof wall to the frog. Nowadays, depending on how much hoof wall is still available after resection, a glue-on shoe is a more likely option.

Sutcliffe says it’s “very, very critical” the debrided area remain open. Covering with hoof patches or filling in with acrylics or other composite material creates a perfect environment for the anaerobic fungi and bacteria to proliferate, causing the infection to spread.

After debriding, the problem then becomes a management issue. The hoof is trimmed every four to six weeks depending on growth, with a focus on maintaining the stability of the hoof capsule. The owner will usually then be instructed by the farrier or vet to apply topical anti-fungal or anti-bacterial products such as hydrogen peroxide, iodine, copper sulfate or commercial preparations. Keeping the horse’s feet scrupulously clean and dry is also important at this time.

“What I typically do is leave the owner with a horseshoe nail so they can poke around the edges of the debrided area and make sure the infection isn’t re-establishing anywhere. If it is, they will see some cheesy stuff they can hook out with the nail between the hard wall and the laminae,” said Sutcliffe.

Depending on how much of the hoof is removed, the treatment process could range from a couple of shoeing/trimming cycles to a full year. It also involves correcting the primary cause, if this has been determined.

Although horses can develop white line disease no matter what their circumstances, some general husbandry standards certainly aren’t going to hurt efforts to prevent or minimize it.

Clean stalls and paddock regularly and provide dry bedding.
Schedule regular farriery visits to prevent strain from imbalances or too-long toes. The farrier will also be able to detect infection before it’s gone too far.
Ensure a balanced diet, and, if necessary add a commercial supplement to promote strong hooves and stimulate growth.
Provide regular exercise.
Pick hooves daily for the sake of regular hygiene and to check for early signs of white line disease.

The prognosis for resolution of the disease is good in most cases, especially with early diagnosis and diligent aftercare by the owner and consistent trimming.