Bit & Bridle

Equine White Line Disease (Seedy Toe)

Other Names

  • White Line Disease
  • Seedy Toe
  • Keratinolytic Disease of the Zona Alba (KDZA)
  • Hollow Wall

What is White Line Disease in Horses?

White Line Disease, commonly called Seedy Toe, is a progressive hoof condition characterised by separation and deterioration of the inner hoof wall. The condition begins at the white line — the junction between the hoof wall and the sole — where opportunistic bacteria and fungi exploit any weakness in the structure to colonise and break down hoof tissue.

As the infection takes hold, the affected area becomes soft, chalky, and crumbly, often with a foul smell. The cavity can extend upward through the hoof wall, sometimes reaching as high as the coronary band if left untreated. In severe cases, the structural integrity of the hoof is compromised, placing additional stress on the sensitive laminae beneath and potentially triggering secondary complications including laminitis.

White Line Disease can affect horses of any breed, age, or discipline, though horses kept in chronically wet or dirty environments are at considerably higher risk. The condition is rarely painful in its early stages, which means it can progress significantly before an owner notices anything amiss.

Causes of White Line Disease

The exact causative agents are not fully established, but both anaerobic bacteria (particularly Clostridium species) and keratinolytic fungi are consistently implicated. These organisms are opportunistic — they do not cause disease in a healthy, intact hoof wall, but exploit existing weaknesses:

  • Poor hoof wall quality or conformation, leading to uneven load distribution
  • Prolonged exposure to moisture, mud, or urine-soaked bedding, softening the hoof wall
  • Prolonged dry conditions causing hoof wall cracks and fissures
  • Long intervals between farrier visits, allowing the hoof to distort
  • Chronic laminitis, which disrupts the lamellar bond and creates separation at the white line
  • Previous hoof injuries, nail holes, or poor shoeing technique
  • Dietary imbalances affecting hoof wall quality, including biotin or zinc deficiency

Symptoms and Signs

White Line Disease often presents with subtle signs in the early stages. As an owner, look for:

  • A crumbly, chalky or soft area at the white line, particularly around the toe or quarters
  • A hollow sound when tapping the hoof wall with a hammer
  • Visible separation between the hoof wall and sole
  • Dark, grey, or black discolouration in the white line region
  • Unpleasant odour from the affected area
  • Lameness (usually only in advanced cases or when secondary laminitis develops)
  • Widening or distortion of the white line on hoof pick inspection

In mild cases, the horse may show no signs of discomfort at all. This is why regular farrier visits and attentive hoof care are so important for early detection.

Diagnosis

Diagnosis is primarily clinical. Your farrier or vet will:

  • Inspect the hoof wall and white line visually and with hoof testers
  • Use a hoof knife or probe to assess the extent of separation and cavity depth
  • Tap the wall with a hammer to identify hollow areas
  • In advanced cases, radiographs (X-rays) may be taken to assess whether the pedal bone has rotated or the infection has tracked upward toward sensitive structures

Distinguishing White Line Disease from other hoof wall separations, such as those caused by laminitis alone, can require careful examination. Your vet and farrier should ideally assess the case together.

Treatment

Treatment depends on the severity of the disease but follows the same core principle: remove all infected tissue, expose the cavity to air, and keep it clean.

  1. Debridement: The farrier removes the overlying hoof wall using nippers, a hoof knife, or a Dremel burr. All infected, crumbly material must be removed until only clean, solid hoof tissue remains. This can look alarming, but exposing the cavity is necessary — the organisms thrive in the airless environment beneath the wall.
  2. Topical treatment: The exposed area is treated with topical antifungal or antibacterial agents. Common choices include iodine solution (applied daily until the tissue is dry and clean), copper sulphate, or commercially available hoof treatments. Your vet may prescribe a specific topical in severe cases.
  3. Therapeutic shoeing: The farrier may apply a heart-bar shoe, wide-webbed shoe, or a glue-on shoe to redistribute weight-bearing forces away from the damaged area and protect the thinned wall during regrowth.
  4. Environmental management: The horse must be kept in a clean, dry environment. Standing in mud or wet bedding will re-infect the cavity and prolong recovery.
  5. Ongoing monitoring: Regular farrier visits are essential during recovery — typically every 4–6 weeks — to ensure the hoof wall is growing back cleanly and no infection remains.

Prevention

Prevention is straightforward but requires consistency:

  • Regular farrier visits every 6–8 weeks — never let the hooves grow beyond reasonable length
  • Daily hoof picking and inspection
  • Keep stables clean, dry, and well-bedded
  • Avoid prolonged standing in mud or wet paddocks — consider sacrificial areas or pea gravel for high-traffic zones
  • Maintain a balanced diet; consult your vet about biotin, zinc, and methionine supplementation if hoof quality is consistently poor
  • Address any underlying laminitis promptly and work with your farrier on therapeutic management

Prognosis

The prognosis for White Line Disease is generally good when caught early and treated promptly. Mild to moderate cases resolve fully with debridement, topical treatment, and improved management, though hoof regrowth takes time — the hoof wall grows at approximately 8–10 mm per month, so a severe case requiring removal of a large section may take 9–12 months to fully grow out.

Advanced cases with significant wall destruction, secondary laminitis, or infection tracking to the coronary band carry a more guarded prognosis, particularly if pedal bone damage has occurred.

When to Call the Vet

Contact your vet if:

  • The horse is noticeably lame alongside hoof wall changes
  • The separation extends high toward the coronary band
  • You suspect concurrent laminitis
  • Topical treatment and debridement are not resolving the cavity within 4–6 weeks
  • There is swelling, heat, or discharge at the coronary band
  • The horse is reluctant to bear weight on the affected limb

For most straightforward cases, your farrier will be the primary person managing White Line Disease in partnership with your vet. Early intervention is always best.

Frequently Asked Questions

Can White Line Disease spread to other horses?

White Line Disease is not contagious between horses. The bacteria and fungi that cause it are environmental organisms present in most stables and paddocks. However, if one horse is developing it in a particular environment, other horses in the same conditions are also at elevated risk — so review your management practices if you see it in your herd.

How long does it take for the hoof to recover from White Line Disease?

This depends heavily on severity. Minor cases with small cavities may resolve and grow out within 3–4 months. Severe cases with extensive wall removal can take 9–12 months for full hoof wall regrowth. Throughout recovery, regular farrier visits are essential to monitor progress and maintain correct trimming.

Is White Line Disease the same as thrush?

No. Thrush is a bacterial infection of the frog and sulci (the grooves alongside the frog), while White Line Disease affects the hoof wall and white line. Both thrive in dirty, moist environments and can occur simultaneously, but they are distinct conditions requiring different treatments. Thrush is typically more obvious from the smell and frog texture, while White Line Disease shows as separation or crumbling at the wall.

Can a horse with White Line Disease continue working?

In mild cases where there is no lameness, many horses continue light work during treatment. Your farrier and vet should advise based on the extent of the disease, the quality of the remaining hoof wall, and whether the horse is shod therapeutically. Avoid hard or stony ground during treatment. Horses with concurrent lameness should be rested until cleared by your vet.