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. 
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. 
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. 
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. 
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. 
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. 
Proposed risk factors for hoof wall separation which precedes white line disease, include: 
- 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
- Wet, humid conditions:These conditions can soften the hoof and allow debris to enter the separation which brings bacteria and fungi into the area
- Hot, arid conditions: These conditions can make the hoof more brittle and prone to cracking, fissures and separation
- 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: 
- 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 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. 
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.  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. 
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. 
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: 
- 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. 
After complete recovery when the resected area has fully grown out, the sole / hoof wall junction should be thoroughly assessed by the farrier on a regular 4-5 week re-shoeing schedule.
If frequent and appropriate farriery is used, most cases will show healthy regrowth and complete recovery.
In an anecdotal report by farriers who have dealt with over 100 cases of white line disease, 70% of cases showed complete resolution. 
The remaining 30% were either lost to follow-up or the owners did not adequately comply with regular farriery.
Horses who have resolved cases of white line disease are at higher risk of developing hoof wall separation again. These horses should be monitored carefully during routine hoof care to identify hoof wall separation early and provide appropriate hoof care.
Whenever possible any area of hoof wall separation should be removed down to the area of solid attachment.
The exact cause(s) of hoof wall separation and subsequent white line disease are not well-defined. Precise guidelines for prevention have not been established.
However, basic principles for supporting hoof health and growth should be followed for all horses.
Proper Hoof Care
Prevention and maintaining hoof health includes routine hoof care. The horse’s hooves should be regularly cleaned to remove dirt and debris from the soles to decrease the chance of microbes infiltrating any cracks or fissures.
Proper farriery to maintain a strong hoof wall/sole junction and with plans to correct issues such as long toes or underrun heels should be prioritized.
This is beneficial for supporting distribution of weight-bearing in the hoof and potentially decreasing the mechanical strain that can exacerbate hoof wall separation.
Excess moisture also plays a role in softening the hoof and making it more susceptible to breakdown and microbial infection. Moisture makes the hoof wall swell and expand.
As much as possible, remove your horse from the source of moisture by stabling at night or keeping them out on a sandy dry lot. In moist conditions, consider adding 2-3 tablespoons of salt to their hoof oil/conditioner and using this daily.
Salt naturally draws moisture; by applying salt to the exterior hoof wall you can help pull moisture out. 
Feeding Plans for Hoof Health
The hoof wall is a slow-growing, dense tissue that is abundant in the protein keratin.
- Biotin: This B-vitamin is an important co-factor for several enzymes and contributes sulfur which is required for making keratin
- Zinc and copper: A proper balance of the microminerals zinc and copper supports keratin synthesis and provides antioxidant protection
- Amino acids: Keratin, like all proteins, is made of amino acids
The link between biotin and hoof health is well-established. It is important to ensure your horse is getting at least 20 mg of biotin in their ration per day to support hoof growth and recovery from white line disease.
Several studies have found that 15 – 20 mg per day of biotin is beneficial for improving hoof hardness and supporting faster growth. Larger breeds or those with a heavy work load may benefit from up to 30 mg per day. 
Copper and Zinc
In one study, a lower incidence of hoof wall separation and white line disease was observed in horses that were meeting their zinc and copper requirements.
Feeding the right amount of copper and zinc is important, but it is also important to supply the correct balanced ratio and delivery form of these minerals. 
Zinc, copper and iron compete for the same absorption pathways in the gut.  High levels of iron in the diet can interfere with zinc and copper absorption and contribute to issues with hoof health.
Equine nutritionists generally target an iron to zinc to copper ratio of 4:3:1. This supports optimal absorption of zinc and copper with minimal interference by iron.
Iron is commonly high in forages and water. Equine diets typically exceed iron requirements, which can contribute to poor hoof health.
It is strongly advised to avoid feeds that contain added iron. These are often listed in the ingredients section as ferrous sulphate, iron oxide, or iron amino acid complex, among others.
Also check to make sure your horse’s mineral and vitamin supplement provides copper and zinc in their organic form as opposed to inorganic forms. Organic trace minerals are better absorbed and utilized by the body.
Examples of organic minerals include zinc and copper proteinates which provide the mineral bound to amino acids. This allows the minerals to be absorbed in the gut in the same manner as amino acids, bypassing the copper/zinc/iron channels and avoiding interference by iron.
Keratin protein in hooves is made up of a string of amino acids bound to each other and folded into the correct structure. This requires several essential amino acids that must be provided in the horse’s diet, including lysine, methionine and threonine.
Diets that are low in protein might be lacking these amino acids. Protein sources such as soybean meal or alfalfa hay are good options for boosting the protein and amino acid supply of the diet.
Supplements for Hoof Growth
Mad Barn’s vitamin and mineral supplement AminoTrace+ provides 20 mg of biotin per serving, along with organic zinc and copper in the proper ratio.
This supplement also contain added amino acids to help meet the requirements for optimal protein synthesis in the body. AminoTrace+ also supplies complete B-vitamin fortification, natural vitamin E, magnesium and a full complex of additional nutrients that horses need in their diets.
Horses with long-standing hoof health issues such as hoof wall separation, white line disease or with high iron intake, should be supplemented with AminoTrace+ to support strong, healthy hoof growth.
For help with formulating a diet to support hoof health or address poor hoof condition, submit your horse’s diet online for a free evaluation.
Is Your Horse's Diet Missing Anything?
Identify gaps in your horse's nutrition program to optimize their well-being.
- O’Grady, S. and Burns, T.D. White line disease: A review (1998-2018). Equine Vet Edu. 2019.
- Apprich, V. et al. Scanning electron microscopy and fungal culture of hoof horn from horses suffering from onychomycosis. Vet Dermatol. 2010.
- O’Grady, S. A fresh look at white line disease. Equine Vet Edu. 2011.
- Kuwano, A. et al. A survey of white line disease in Japanese racehorses. Equine Vet J. 1999.
- Celeste, C.J and Szoke, M.O. Management of equine hoof injuries. Veterinary Clinics: Equine Pract. 2005.
- Comben, N. et al. Clinical observations on the response of equine hoof defects to dietary supplementation with biotin. Vet Rec. 1984.
- Josseck, H. et al. Hoof horn abnormalities in Lipizzaner horses and the effect of dietary on macroscopic aspects of hoof horn quality. Equine Vet J. 1995.
- Geyer, H. and Schulze, J. The long-term influence of biotin supplementation on hoof horn quality in horses. Schweizer Archiv fur Tierheilkunde. 1993.
- Reilly, J.D., et al. Effect of supplementary dietary biotin on hoof growth and hoof growth rate in ponies: a controlled trial. Equine Vet J. 2010.
- Buffa, Eugene et al. Effect of dietary biotin supplement on equine hoof horn growth rate and hardness. Equine Vet J. 1992.
- Higami, A. Occurence of white line disease in performance horses fed on low-zinc and low-copper diets. J Equine Sci. 1999.
- Mills, CF. Dietary interactions involving the trace elements. Annu Rev Nutr. 1985.