A healthy hoof is usually a trustworthy indicator of a healthy horse – smooth, well-trimmed, and well-kept hooves offer support and protection against some ground hazards. However, even under the most watchful of equine handlers, issues can still arise that attack and damage the structure of the hoof from within, progressing insidiously over time. A common hoof problem, white line disease in horses, can start unbeknownst to both horse and handler and has no distinct cause, making it an ever-looming threat to equine health. Left untreated, it can and will progress to the point that affects the gait, comfort, and even overall health of the horse. The disease’s opportunistic bacteria and fungi move deeper into the hoof structure. 

Contrary to what the name may indicate, there are rarely any initial outward signs of white line disease, or WLD, on the shiny outer wall of the hoof itself. Instead, the separation of the hoof wall from the “white zone” just behind it, and the lamella layer on the underside, will be where the disease is primarily noticed and diagnosed. 

White line disease may also be called by a few other names, depending on the handler or medical professional discussing it; the disorder is also known as seedy toe (referring to debris forced into the hoof), hollow wall (indicating the symptom effects), and onychomycosis (from the Latin word for “fungal nail infection”). However, no matter what name it goes by, there is one universal truth in the equine world: it spells trouble. 

How Is White Line Disease In Horses Diagnosed?

A farrier (a person who shoes horses) will usually be the horse’s first line of defense where white line disease is concerned, as they’re far more likely than a handler to notice subtle foot structure changes on the underside of the hoof. Several “lookalike” conditions may mimic the signs of WLD, so you may need specific tests for the horse to rule them out. A misdiagnosis – and consequent incorrect treatment – could have negative long-term effects on lameness, gait, and comfort of an affected horse.

Before picking up a hoof and fearing the worst, remember that, like most diseases, it takes a professional to see the truth. There are two main “lookalikes” for the symptoms of white line disease in horses:

• White Line Disease vs. Laminitis: The inflammation-heralded laminitis is a familiar foe to most horse handlers; it can show up as an acute occurrence (triggered by a specific event), recurrent (cyclical appearances after an acute appearance), or chronic (gradual reappearance triggered by other health concerns, such as diet.) The primary difference between WLD and laminitis is how the coffin bone – a structure in the core of the hoof – is compromised. While WLD-affected X-rays may still show the unwanted rotation of this structure, mimicking laminitis, an equine vet should be able to discern, via severity and placement, which disorder is at play.

• White Line Disease vs. Thrush: More than the ailment that’s notorious for making infants uncomfortable, equine thrush is an infection caused primarily by bacteria but may also be triggered by certain strains of fungus. In horse hooves, thrush will affect the frog or rear of the hoof rather than the front wall, where WLD will usually manifest. True thrush will also produce a tarry black substance when a hoof pick is employed and accompanied by a foul smell.

Ruling these in or out will require an in-depth examination of the horse and potentially an x-ray to check the position of the coffin bone. 

Is White Line Disease Contagious?

With such a serious illness attacking one of the most vulnerable parts of a horse’s anatomy, it’s only natural that a handler’s worries would drift to the rest of their animals. Thankfully, white line disease is not contagious – rather than being its own entity, it’s more of an overarching term that covers opportunistic infections of the hoof. White line disease is also not zoonotic, meaning a horse cannot “pass it on” to his human handler. 

While areas of environment and care can contribute to a white line disease appearance, they usually don’t point to risk for other nearby horses. Just the same as one horse might not tolerate a certain food while another digests it without issue, much of the susceptibility factor rests on the health of an individual horse. That said, a diagnosis of WLD in one paddock animal should indicate a cautionary assessment of diet and environmental conditions for the rest. Also, out of an abundance of caution, handlers should not use the same tools (e.g., hoof picks) on both affected and healthy horses.  

As the disease is opportunistic and bacteria and fungi thrive in wet conditions, you should change stall bedding and hay frequently. Whenever possible, landscaping or finishing a paddock to prevent standing water or marshy ground will help lower infection risks. 

Treatment For White Line Disease In Horses

This familiar yet concerning equine hoof disorder lodges and spreads because it “burrows” in, thriving beneath the protective layer of the outer hoof wall and the inner lamella. This positioning prevents it from being dislodged through movement or washed away with rain or damp terrain. The more debris, moisture, and dirt that is packed into a separated or compromised hoof wall through movement, the more chance WLD has to thrive and grow. Therefore, a horse’s handler should focus on preventing further impaction – e.g., trimming, filling, or covering damaged parts of the hoof if necessary – and sterilizing any affected areas with appropriate medication as prescribed by a vet.

Treatment for white line disease in horses, once diagnosed, follows these paths closely. A handler may need to apply a daily coating of iodine to the hoof, for example, or compel the horse to stand in a vet-approved chlorine solution, the latter also being a go-to approach to killing off thrush in the hoof. 

In advanced cases of WLD, meaning those that are “caught” in advanced stages on those that have been allowed to do damage, corrective bars or horseshoes may be needed. They may be used in conjunction with other methods, such as restorative putty, to help balance the foot and protect the hoof interior. The goal in any white line disease treatment for horses is to protect the integrity of the foot to ensure an awkward gait or hoof trauma doesn’t permanently affect comfortable walking and trotting ability. 

Suppose the diet is determined to be a factor in white line disease flare-ups. In that case, an equine veterinarian may recommend a change in food or hay, adjustment of feeding schedules, new shoeing practices, or even an environment change. In most cases, a vet already familiar with the horse can make these decisions and offer guidance. A discussion with a horse’s regular farrier can also ensure that any physical correctional requirements go as smoothly as possible.

Treating White Line Disease Symptoms In Horses

Understandably, the separation and infection of an inner layer of the hoof can manifest as anything from a mild irritant to a sharp pain that directly causes lameness. Keeping a horse feeling healthy and walking correctly is essential to avoid long-term adverse effects when dealing with white line disease. This is the primary reason that both steroid and non-steroidal treatments are usually administered to affected horses, helping them keep painful inflammation to a minimum. Without treatment to reduce pain and discomfort, WLD can quickly become a vicious loop: an affected horse walks tenderly or lamely, increasing pressure and pain in an improperly-seated hoof stance, which in turn lowers their resistance – both immunity-wise and in the physical growth of the hoof – to fight off the effects of WLD.

In conclusion, handlers should keep track of any days they notice a horse or horses performing at less than their best: even if WLD isn’t immediately visually apparent, horses’ behavior can hint at discomfort well before the physical symptoms are visible. This may be as simple as sluggish performance or hesitation on a trail ride, or it may take the form of more casual observation of horse movements while out grazing or exploring. This track record will also help an equine vet-farrier-handler team determine the best ways to heal and eliminate the presence of white line disease. If a horse is suffering from WLD, he should not be shown or required to do intense work until a vet gives him a passing grade for hoof health. If pushed, strenuous activity may trigger a surge of the disease; therefore, thoughtful care and mindful treatment are required.

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Sources Cited:

1)  Loving, Nancy S. “The Frustrations of White Line Disease.” The Horse (thehorse.com), August 6, 2019, https://thehorse.com/113282/the-frustrations-of-white-line-disease/. Accessed April 15, 2021.

2)   Oakford, Glenye. “Hoof Help: White Line Disease.” US Equestrian (usef.org), December 19, 2017, https://www.usef.org/media/equestrian-weekly/hoof-help-white-line-disease. Accessed April 15, 2021.

3)   “White Line Disease: Identifying, Treating and Preventing.” AQHA | American Quarter Horse Association (aqha.com), November 12, 2020, https://www.aqha.com/-/white-line-disease. Accessed April 15, 2021.

4)   Belknap, James K., DVM, PhD, DACVS, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University. “Disease in Horses.” Merck Manual Veterinary Manual (merckvetmanual.com), October 2015, https://www.merckvetmanual.com/musculoskeletal-system/lameness-in-horses/white-line-disease-in-horses. Accessed April 15, 2021.

5)  “The Facts About Chronic Laminitis.” EQUUS (equusmagazine.com), March 10, 2017, https://equusmagazine.com/diseases/chroniclaminitis_032006. Accessed April 15, 2021.