White line disease is a hoof condition that can lead to pain and lameness. This condition affects the equine hoof wall in one or more hooves at a time.

White line disease originates as a separation between adjacent layers in the hoof wall starting at the toe, quarter, and/or heel, which can then become infected with bacteria and fungi.

The separation occurs between the stratum medium and stratum internum within the non-pigmented area known as the white line.

As separation progresses upwards towards the coronet, it can cause significant pain and discomfort and affect the horse’s mobility.

Common treatment involves resection of the affected tissue and appropriate farrier care to promote comfort.

Supporting hoof re-growth after resection is important for recovery from white line disease. For help with formulating a diet to support hoof health, get in touch with our nutritionists.

What is White Line Disease?

White line disease always occurs after hoof wall separation which can begin at the toe, quarter and/or heel of the hoof. This area may become infected with bacteria or fungi which break down hoof wall tissue.

Hoof wall separation is quite common in horses but does not always lead to white line disease. Farriers routinely find separations that reach 0.5 to 2 cm in depth.

Some horses with hoof wall separation may never show signs of bacterial or fungal infiltration. Instead, their separation can be removed through regular hoof care or it may remain stable over time. [1]

In horses that develop white line disease, the area is infiltrated by bacteria or fungi which produce enzymes that breakdown keratin – the main protein in the hoof wall. This can lead to further separation that progresses upwards towards the coronet.

The presence of fungi within the separation damages cells of the hoof horn which can ultimately lead to weak hoof structure, reduced performance and lameness. [2]

Seedy Toe & Onychomycosis

Other names for this condition include seedy toe, hoof wall disease, hollow hoof and onychomycosis. However, these terms are sometimes used to describe a specific type of hoof issue. [1]

For example, seedy toe is a term used when the separation occurs specifically at the toe. This is often due to poor hoof conformation including long toes or club foot which decreases blood flow to the area leading to tissue death and separation of the hoof wall.

The term Onychomycosis is sometimes used when fungal microorganisms such as Trichophyton spp and Scopulariopsis brevicaulis have been detected. [2]

However, onychomycosis specifically refers to fungal infection of the skin or nail bed. This is not where the fungal infection occurs in horses with white line disease. [3]

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Risk Factors

The exact cause(s) of hoof wall separation and white line disease are not yet known.

White line disease can affect horses of any age, gender or breed. It can occur in one or more hooves and occurs in barefoot and shoed horses.

In a 1996 survey of racehorses in Japan, 11.5% of horses were found to have white line disease. This was defined as visual assessment of damaged white line even with regular hoof care.

In this survey, older horses (4 and 5 years of age) were more affected than younger horses (2 years of age). They also observed that lesions were most likely to occur at the toe and were more common in the fore feet than the hind feet. [4]

Proposed risk factors for hoof wall separation which precedes white line disease, include: [1]

  1. Hoof conformation: Certain hoof conformations put additional strain on the hoof wall that can lead to separation, including long toe and/or underrun heel, clubfoot, sheared heels
  2. Wet, humid conditions:These conditions can soften the hoof and allow debris to enter the separation which brings bacteria and fungi into the area
  3. Hot, arid conditions: These conditions can make the hoof more brittle and prone to cracking, fissures and separation
  4. Vascular damage: Injuries or hoof conformation that impairs blood flow to the hoof wall can lead to tissue death and hoof wall separation

Reducing the Risk

Consistent hoof care involving removal of dirt from the sole is beneficial for reducing debris and pathogens that can enter hoof wall separations.

Appropriate farriery is also required to support proper hoof conformation and to minimize excessive mechanical strain that can perpetuate hoof wall separation.

Wet conditions might be difficult to avoid, but if you have a choice of pastures then keeping your horse out of damp fields can reduce the risk. Excessive washing or bathing may be detrimental to hoof health and should be avoided whenever possible.

Signs of White Line Disease

Horses often don’t show any signs of discomfort until the hoof wall separation and white line disease has progressed significantly.

Your farrier may notice hoof wall separation during routine hoof care. Depending on the depth of the separation, they can clean out the debris and reach the area of solid connection between the hoof wall and the white line.

If the separation is deep, the area may become filled with grey/white powdery hoof material indicative of damaged tissue.

Early signs of white line disease include: [1]

  • Tender soles
  • Temporary heat in the feet
  • Flattening sole in the area near the separation
  • Slow hoof wall growth
  • Hollow sound when hoof wall is tapped

In more advanced cases, noticeable changes in the shape of the hoof capsule can become apparent. The attachment between the hoof wall and the distal phalanx can be weakened which can cause rotation and changes in the hoof conformation.

When there is rotation, there can be indentation (a concavity or “dish”) in one area of the hoof and a bulge on the opposite side.

Horses that have progressed to this advanced state of hoof wall separation and white line disease will likely show lameness and discomfort.

In advanced cases, where separation has progressed significantly, the hoof capsule can become distorted and the distal phalanx may rotate within the hoof capsule. These cases require extensive rehabilitation with corrective shoeing and stall-rest.

Diagnosis

Diagnosis is typically based on observation of a hoof wall separation where the white line appears wider and softer than normal.

It may also have a waxy texture and be filled with grey/white soft horn material or have black fluid draining from the separation. [1]

If a horse is showing discomfort, local analgesic can be used to identify the precise location that is triggering a pain response.

Radiographs (x-rays) can be useful to show the extent of separation and whether there is rotation within the hoof capsule. This can help distinguish between white line disease and laminitis without hoof wall separation.

In research studies, fungi and bacteria have been isolated from samples taken from the affected hoof area. [2] However, this is not commonly used as a diagnostic technique as the sample can easily be contaminated and yield unreliable information.

Treatment and Recovery

Treatment and rehabilitation of the hoof rely on skilled farriery and resection of the affected tissue. [1]

During the early stages, with minimal hoof wall separation, your farrier may opt to fill the separation with medicated putty before shoeing.

Any underlying hoof conformation issues such as long toe and underrun heels should be addressed to decrease the mechanical strain that can perpetuate hoof wall separation.

Your farrier may need to use specific shoeing techniques to help correct hoof wall distortions. They will also support the horse’s comfort by using corrective shoeing to redistribute weight bearing off of the sole and away from the damaged area. [1]

This can help prevent further hoof wall separation and decrease the risk of distal phalanx rotation and lameness.

Hoof wall resection

In advanced cases where hoof wall separation has progressed extensively upwards, resection of the hoof wall will likely be required. This involves removing the outer hoof wall to expose the affected area.

The resection continues upwards and sideways around the area to ensure the edges of the resection are areas of solid attachment between the hoof wall and the underlying structure.

The resected area should remain exposed and dry as the hoof wall regrows. Strategies for keeping the resected area clean and dry during regrowth include: [1]

  • Using dry bedding such as sawdust or wood shavings
  • Keeping the bedding clean and dry
  • Avoiding turnout during wet conditions
  • Delaying turnout in the morning to when the grass is no longer dewy
  • Avoiding the use of hoof boots which can trap moisture

The area will need to be frequently tended by a farrier as it grows out. Farrier visits may need to occur as frequently as every 2 weeks to support proper healing.

It is advised to clean the resected area daily with a wire brush. [1]