English
![White Line Disease in Horses [Causes, Symptoms, Treatment & Recovery]](/wp-content/uploads/2021/09/White-Line-Disease-in-Horses-Causes-and-Recovery.jpg)
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 (WLD) 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. The characteristic of white line disease is separation that extends above the level of the live sole plane.
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 break down 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. However, seedy toe involves the sole-wall junction, not the inner layer of the sole. It never progresses into live tissue but may result in cracks. [3]
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 in humans and dogs, producing abnormal, thickened nail tissue. This is not where the fungal infection occurs in horses with white line disease. In WLD, damage is restricted to destruction of the soft junction between the unpigmented stratum internum and the pigmented outer layer of stratum medium. [3]
What's your top priority with your horse's health?
What's your top priority with your horse's health?
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]
- 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. The hoof below the live sole plane is dead, like our fingernails. The white line can dry out and crumble.
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 have 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 of the coffin bone and flaring of the hoof wall.
When there is rotation, there can be indentation (a concavity or “dish”) on the dorsal hoof wall along with a bulging sole.
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]
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.
Prognosis
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. [1]
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.
Prevention
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.
Feeding Plans for Hoof Health
The hoof wall is a slow-growing, dense tissue that is abundant in the protein keratin.
Optimal keratin synthesis to promote strong hoof growth requires several key nutrients. This includes biotin, zinc, copper and amino acids.
- 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. [5][6][7][8][9]
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. [10]
Zinc, copper and iron compete for the same absorption pathways in the gut. [11] 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.
Amino Acids
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, ground flax seed, or alfalfa hay are good options for boosting the protein and amino acid supply of the diet, but may be low in methionine.
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 contains 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.
Frequently Asked Questions
Here are some frequently asked questions about White Line Disease in horses:
White Line Disease is a hoof condition that develops when separation occurs between layers of the hoof wall and becomes infiltrated by bacteria or fungi. The separation typically begins at the toe, quarter, or heel and may progress upward toward the coronet if left untreated. As the hoof wall weakens, affected horses may develop pain, reduced performance, lameness, and structural instability in the hoof capsule. [1][2]
White Line Disease affects the non-pigmented junction between the stratum medium and stratum internum of the hoof wall. This area is commonly referred to as the white line, although the disease actually damages the soft connection between the inner and outer hoof wall layers. When this junction breaks down, the hoof wall can separate and create a pocket where debris and microbes accumulate. [1][3]
White Line Disease and seedy toe are related terms, but they are not always used in exactly the same way. Seedy toe usually refers to separation at the toe involving the sole-wall junction, while White Line Disease can occur at the toe, quarter, or heel and may extend higher within the hoof wall. [1][3] Other names sometimes used include hoof wall disease, hollow hoof, and onychomycosis.
White Line Disease occurs after hoof wall separation, but the exact cause of that separation is not fully understood. Once a separation forms, opportunistic bacteria or fungi can enter and produce enzymes that break down keratin, the main protein in the hoof wall. [2] This weakens the hoof horn and allows the separation to progress farther upward.
White Line Disease can affect horses of any age, breed, or sex, and it can occur in barefoot or shod horses. Risk factors include hoof conformation problems such as long toes, underrun heels, club feet, or sheared heels, because these increase mechanical strain on the hoof wall. [1] Wet or humid conditions can soften the hoof and allow debris to enter separations, while hot, dry conditions can make the hoof more brittle and prone to cracking. [4]
Early signs of White Line Disease can be subtle, and many horses do not show obvious discomfort until the condition is more advanced. A farrier may first notice hoof wall separation, a widened or softer white line, grey or white powdery material, a hollow sound when the hoof wall is tapped, tender soles, temporary heat in the feet, slow hoof growth, or flattening of the sole near the separation. [1]
Advanced White Line Disease in horses can cause visible distortion of the hoof capsule, flaring of the hoof wall, lameness, and discomfort. If the attachment between the hoof wall and coffin bone weakens significantly, the distal phalanx can rotate within the hoof capsule. This may create a concave or dished appearance on the dorsal hoof wall, a bulging sole, and a need for extensive rehabilitation with corrective shoeing and stall rest.
White Line Disease is typically diagnosed by observing hoof wall separation where the white line appears wider, softer, waxy, or filled with grey-white crumbly horn material. [1] Radiographs may be recommended to determine how far the separation extends and whether there is rotation within the hoof capsule. X-rays can also help distinguish White Line Disease from laminitis when hoof wall separation is present.
Treatment for White Line Disease focuses on removing diseased hoof tissue, correcting mechanical strain, and supporting healthy hoof regrowth. Mild cases may be cleaned out and filled with medicated putty before shoeing, while more advanced cases often require hoof wall resection to expose and remove affected tissue. [1] Corrective trimming and shoeing may also be needed to redistribute weight away from the damaged area and prevent further separation.
Hoof wall resection is a treatment used when White Line Disease has progressed extensively upward within the hoof wall. It involves removing the outer hoof wall over the affected area until the farrier reaches solid attachment around the edges of the separation. [1] The exposed area is then kept clean, dry, and open while the hoof wall gradually regrows.
How quickly a horse recovers from White Line Disease depends on how much of the hoof wall is affected and how long it takes healthy horn to grow back. The resected area often needs frequent farrier care, sometimes as often as every two weeks during regrowth. [1] After full recovery, horses should remain on a regular four- to five-week hoof care schedule so any new separations can be identified and addressed early.
The prognosis for White Line Disease is generally good when horses receive appropriate and consistent farrier care. In one anecdotal report from farriers who managed more than 100 cases, 70% of horses had complete resolution. [1] Horses that have recovered remain at higher risk of future hoof wall separation, so ongoing monitoring is important.
Preventing White Line Disease involves reducing hoof wall separation and limiting exposure to moisture, debris, and microorganisms. Regular hoof cleaning, routine farrier care, correcting long toes or underrun heels, and avoiding excessive mechanical strain can all help support a stronger hoof wall-sole junction. Keeping horses out of damp fields when possible, avoiding excessive bathing, and using clean, dry bedding can also reduce risk.
Nutrition can support hoof regrowth after White Line Disease by providing the nutrients required for keratin synthesis. Important nutrients include biotin, zinc, copper, and amino acids such as lysine, methionine, and threonine. Horses recovering from hoof wall separation or poor hoof quality should receive a balanced diet that supports strong hoof growth and avoids deficiencies that may slow recovery.
Zinc and copper support keratin synthesis, antioxidant protection, and strong hoof horn formation. Horses meeting their zinc and copper requirements have been observed to have a lower incidence of hoof wall separation and White Line Disease. [10] Because iron can interfere with zinc and copper absorption, many hoof-focused diets aim for an iron-to-zinc-to-copper ratio of approximately 4:3:1 and avoid feeds with added iron. [11]
Summary
White line disease (WLD) is a hoof-wall separation that begins at the white line (between the stratum medium and stratum internum) and can become infected with bacteria and fungi, causing pain and lameness.
- Separation often starts at the toe, quarters, or heels and, if it progresses upward toward the coronet, can distort the hoof capsule and compromise mobility.
- Risk rises with mechanical stress and environment—long toe/underrun heels, clubfoot or sheared heels, and wet or very dry conditions that soften or brittle the wall and allow debris and microbes to invade.
- Early signs include tender soles, heat, a hollow sound on tapping, powdery degraded horn in the gap, and a widened, waxy white line; radiographs help gauge extent and rule out laminitis/rotation.
- Primary treatment is skilled farriery with debridement/resection of undermined wall, correction of hoof balance, protection to redistribute load, and meticulous management to keep the resected area clean and dry.
- Prevention and recovery hinge on regular hoof care and a hoof-strengthening diet with adequate biotin (≈20–30 mg/day as needed), organic zinc and copper in balanced ratios, and essential amino acids, while avoiding excess dietary iron.
References
- 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. View Summary
- 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. View Summary
- Comben, N. et al. Clinical observations on the response of equine hoof defects to dietary supplementation with biotin. Vet Rec. 1984. View Summary
- 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. View Summary
- 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.
