Vitiligo in horses is a disorder that causes patches of skin and hair to lose their normal colour or pigmentation. This condition is not contagious, painful, or life-threatening, but it can be disconcerting to see your horse’s skin or hair lose it natural colour.

The progression of vitiligo is different in every horse. Patches of colour loss can increase or decrease over time, and in rare cases the skin completely regains its normal pigmentation. However, in most cases, patches of vitiligo spread and never regain their initial colour.

The exact cause of vitiligo remains unknown, but this condition is believed to involve an autoimmune response. Some horses may have a genetic predisposition to vitiligo and environmental triggers, such as sunburn or other skin traumas, might exacerbate the condition.

There is no definitive cure for vitiligo in horses, although topical creams and sun protection may be used to treat the condition. Some nutritional interventions have been reported to improve vitiligo in horses, but there is limited evidence to determine efficacy.

This article examines vitiligo in horses, highlighting its causes, prevalence, progression, diagnosis, available treatments, and nutritional interventions.

Vitiligo in Horses

Vitiligo is an autoimmune condition where the body’s immune system mistakenly targets and destroys melanocytes, the cells responsible for producing melanin. Melanin is the natural skin pigment that gives your horse’s skin and hair coat its colour.

When melanocytes die or are damaged, they stop producing melanin, leading to a gradual fading of colour in skin and hair. The result is the appearance of white or light patches on the skin, which can vary in size and location.

While other conditions, such as ringworm or injuries, can cause white patches on the skin, only the decline of melanin production classifies the condition as vitiligo.

A diagnosis of vitiligo is only made in the absence of injuries, inflammation, or other skin conditions that could explain the loss of colour.

Mad About Horses
Join Dr. Chris Mortensen, PhD on an exciting adventure into the story of the horse and learn how we can make the world a better place for all equines.
Apple Podcasts Spotify Youtube
Mad Barn - Equine Nutrition Consultants | Mad Barn USA

Prevalence

All horses can develop vitiligo, but this condition is much more common in grey horses. 26 – 67% of grey horses develop vitiligo, compared to only 0.8 – 3.5% of non-grey horses. [1][2]

Consequently, breeds with a significant proportion of grey horses tend to exhibit a higher incidence of vitiligo. These breeds include:

Arabian horses are also predisposed to this condition, which was once called Arabian Fading Syndrome. [3] Some consider Arabian Fading Syndrome (also called “Pinky Syndrome”) a sub-type of vitiligo that develops primarily in younger Arabians between the ages of 1 and 2. [3]

The onset of vitiligo is associated with advancing age, as older horses display both a higher occurrence of the condition and more extensive pigment loss. [1]

Vitiligo has moderate to medium heritability, meaning there is a genetic component that that can be passed down through generations. [1]. If your horse’s sire or dam is affected, your horse may have a higher risk of developing vitiligo.

Some researchers believe that rates of vitiligo in horses could be higher than those reported. Since the disease only impacts the horse’s cosmetic appearance and is not painful or contagious, owners may not seek veterinary care or report the condition.

Common Sites for Vitiligo

Vitiligo most commonly occurs around the mucocutaneous junctions on the horse’s body. Mucocutaneous junctions are the areas where the mucosa transitions into the skin.

The areas most frequently affected by vitiligo include:

  • Lips
  • Nostrils
  • Eyelids
  • Anus
  • Vulva
  • Sheath

Vitiligo typically first manifests in the facial region, especially around the lips, muzzle, and eyelids. The anus and vulva are less frequently affected.

In some instances, hooves might also experience a loss of color. Sometimes, the hair can lose its colour while the skin retains normal pigmentation.

Examples of Vitiligo in Horses | Mad Barn USAEquine Vitiligo by Tham et al. is licensed under CC BY 4.0

Disease Progression

The progression of vitiligo varies among horses. Typically, it begins as small patches of pigment loss that expand over time. Occasionally, these patches might diminish in size.

A case study involving an 18-year-old roan gelding noted some patches of pigment loss regressed while new ones formed, or existing ones grew. [4] The image below illustrates the progression of vitiligo in this gelding from 2014 to 2018.

Gelding With Vitilgo on Lips | Mad Barn USAA 4-year case study of vitiligo in a roan horse by Fonteque et al. is licensed under CC BY 4.0

Causes of Vitiligo

Vitiligo is considered to be an idiopathic condition, indicating that it develops spontaneously with no known cause. [1]

The most widely accepted theory is that vitiligo arises due to an autoimmune disorder. This means that the body’s own immune system attacks and damages the melanocytes responsible for producing skin and hair pigments.

Antibodies

In horses with vitiligo, blood tests reveal the presence of antibodies targeting the horses’ own melanocytes. [5] These antibodies are notably absent in horses without the condition.

Antibodies are proteins that play an important role in the immune system, marking cells for elimination. Typically, they flag invaders like bacteria and viruses or malfunctioning cells, signaling that they should be destroyed by the immune system.

When these antibodies mistakenly mark the body’s healthy cells for destruction, it indicates an autoimmune disorder. The presence of antibodies against a horse’s melanocytes supports the theory that vitiligo is caused by an autoimmune response.

Genetic and Other Factors

There’s growing evidence suggesting a genetic predisposition to vitiligo. In grey horses, certain genes have been identified as correlates to the onset of vitiligo. [1]

In humans, the development of vitiligo is often attributed to a combination of immune factors, genetics, environmental triggers, and defects of the melanocytes. [1] Similarly, vitiligo in horses is likely caused by the confluence of several different factors.

Associated Risks

In grey horses, vitiligo is also associated with an increased incidence of melanoma (skin cancer). The link between vitiligo and melanomas is observed in other animals, including Sinclair Swine. [5]

If your grey horse has vitiligo, regularly inspect their skin for melanomas. These typically manifest as black growths, often found under the tail, near the anus, or on the sheath of geldings.

Melanin also plays a role in protecting your horse’s skin from UV rays, and areas of de-pigmentation are more susceptible to sunburns.

To prevent sunburn, apply sunscreen to the affected regions. Using fly masks with nose flaps or UV sheets can further protect these vulnerable spots from UV exposure.

Diagnosis

Diagnosing vitiligo in horses primarily relies on clinical examination and observation of characteristic depigmented or hypopigmented patches on the skin. These patches often appear symmetrically and may gradually expand.

While vitiligo itself doesn’t cause discomfort or itching, the change in skin pigmentation is quite noticeable, especially in darker-skinned horses.

Skin biopsies or scrapings might also be taken to rule out other skin conditions or diseases and to confirm the diagnosis of vitiligo.

The sampled skin will be stained and viewed under a microscope to determine if the melanocytes are damaged or missing. This also helps rule out other potential causes of pigment loss.

Differential Diagnosis

It’s essential to differentiate vitiligo from other conditions that can cause skin depigmentation in horses, such as fungal infections, scars from previous injuries, or other dermatological conditions.

The following factors can also lead to the appearance of white patches on the skin:

Healed Wounds:

  • Wounds resulting from tack damage, pressure sores, freezing, or sunburns often lead to hair depigmentation upon healing.
  • White patches emerging from areas with prior lesions or injuries typically aren’t linked to vitiligo.

Leukoderma Lupus Erythematosus [6]:

  • A rare condition, it causes depigmentation in areas similar to common vitiligo sites like the muzzle and eyes.
  • Affected horses also show hair loss in depigmented areas, accompanied by symptoms like redness, irritation, swelling, or visible skin lesions.

Spotted Leukotrichia:

  • Characterized by small circular white patches (1-3 cm in diameter) on the neck, trunk, and rump with otherwise normal skin.
  • Details about this condition are limited, and it might be a variant of vitiligo [7].

Treatment

Treatment for vitiligo is not medically necessary, since this is a cosmetic syndrome that does not cause the horse pain or harm.

However, some owners opt for treatment to improve their horse’s aesthetic appearance, especially in show horses. It is advised to carefully consider the risks and side effects of treatments, as the benefits are mainly cosmetic. [7]

For humans with facial vitiligo, the typical treatment involves topical glucocorticoids, such as betamethasone or clobetasol. Glucocorticoids are steroid hormones that modulate immune responses.

When using glucocorticoids on horses, it is recommended to use them sparingly and at the minimal effective dose. [7] Potential side effects include dilated and ruptured blood vessels (spider veins) as well as skin infections or necrosis at the application sites.

Moreover, the efficacy of topical glucocorticoids may be limited in horses because their hairs can prevent the penetration of the medication into the skin.

Phototherapy, involving therapeutic exposure to UV light, is commonly used in human patients with vitiligo, but there are no clinical trials using phototherapy on horses.

Treatments involving systemic drugs are not recommended because the side effects outweigh potential benefits for improving the horse’s cosmetic appearance. [7]

Case Studies

In rare cases, horses with vitiligo have experienced clinical improvement or resolution of symptoms following nutritional interventions. These case reports are described below.

However, each case is different with a unique intervention, making it difficult to draw broad conclusions from these isolated reports.

Quarter Horse Filly

A 2-year-old bay Quarter Horse filly rapidly developed white patches around her muzzle and eye, which were increasing in size and quantity.

After her diet was supplemented with vitamins A, D, and E as well as B-complex vitamins, the white patches gradually disappeared over a four-month period. [8]

The filly’s original diet was not reported, so it is unclear if her diet was previously deficient in vitamins.

Young Arabian Horse

A young Arabian horse experienced rapid loss of skin pigmentation around the eyes and muzzles. Copper deficiency was suspected, and the horse was treated with an organic copper supplement.

Within 30 days of copper supplementation, the white patches started returning to their normal colour and eventually disappeared.

The copper supplement was discontinued over the winter, but the white patches recurred the following spring. Copper was subsequently reintroduced to the diet, yielding the same positive results. [9]

Andalusian Studs

An Andalusian stud farm reported vitiligo in 9 grey horses between the ages of 2 – 2.5 years. The horses experienced color loss in the skin and hair around the eyes, muzzle, and for one horse, in the scrotum and umbilical region.

The owner of the stud farm reported full re-pigmentation after feeding carrots at the rate of 4 – 5 kg a day. [10]

The owner also reported that before the skin issues emerged, all the animals had been given a thyro-protein-based product for 2-3 months, possibly at doses exceeding the manufacturer’s recommendation.

Excessive administration of thyroprotein-based products could have caused a vitamin A deficiency and depigmentation. [7]

Summary of Cases

For all the cases reported above, it was theorized that a nutrient deficiency contributed to the original pigment loss. This may be a distinct condition from vitiligo stemming from an autoimmune disorder or from genetic mutations.

Should your horse display white patches, always consult with your veterinarian for a proper diagnosis. Review your horse’s diet to ensure that it is properly balanced and that there are no nutritional deficiencies that could contribute to skin issues.

Nutritional Interventions

Several nutritional interventions have been investigated to treat vitiligo in humans. However, there is limited research on the effects of these interventions on horses or other animals.

Vitamin D

In humans, low levels of vitamin D have been associated with autoimmune disorders, such as vitiligo. [11][12] Additionally, vitamin D helps reduce the build-up of toxic compounds and reduces cell death in melanocytes that are exposed to stressors. [13]

In children, combining vitamin D supplementation with a topical drug is more effective at restoring skin pigmentation than topical treatment alone. [14]

In one study involving skin-whitening cosmetic products, adult females taking vitamin D supplements had higher rates of re-pigmentation compared to those who did not take vitamin D supplements. [15]

However, there are no studies that examine the use of vitamin D on its own as a treatment for vitiligo.

Vitamin E

Vitamin E is a potent antioxidant that is often supplemented for immune-related disorders. In addition to its ability to neutralize toxic compounds, vitamin E may support patients with vitiligo by absorbing certain wavelengths of light to prevent skin damage. [16]

In one study of humans with vitiligo, a combination of vitamin E with phototherapy treatment led to higher rates of re-pigmentation than the phototherapy treatment alone. [17]

However, another study found that while Vitamin E reduced oxidative stress during UV treatments, it did not improve the appearance of the vitiligo. [18]

B-vitamins

Since humans with vitiligo are frequently deficient in folic acid and vitamin B-12, these vitamins are often supplemented as part of a treatment plan. [19][20]

In a human study involving 100 patients with vitiligo, participants were asked to record their sun exposure and intake of vitamin B supplements.

A combination of sun exposure and vitamin B12 and folic acid supplements was more effective at restoring pigmentation than sun exposure or vitamin supplementation alone. [21]

Phenylalanine

Phenylalanine is an essential amino acid that plays a role in melanin formation. Humans with vitiligo have impaired phenylalanine uptake in their skin cells. [22]

In humans, a combination of phenylalanine supplements with light treatment was more effective at stimulating re-pigmentation than light treatment alone. However, no benefits were noted when phenylalanine was supplemented without light treatment. [23]

Zinc

Zinc is a trace mineral that plays important roles in the development of melanin. It is also an important antioxidant for skin cells.

There is limited research on the use of zinc supplements in vitiligo patients. However, one study reported a small improvement in vitiligo when topical steroid treatments were combined with zinc. [24]

Herbs & Antioxidants

A number of herbal supplements and antioxidants have been explored as treatments for vitiligo. However, the evidence for these supplements is mixed and they often lack clinical data to support their claims.

Summary

  • Vitiligo is a cosmetic syndrome caused by an autoimmune disorder that is not contagious
  • In horses affected by vitiligo, destruction of melanocytes results in white patches on the skin and hair
  • In most cases of vitiligo, the loss of pigmentation is permanent, and colour does not return to the affected area
  • Generally, treatment is not required since the condition is superficial and does not affect the health or function of the horse
  • Sun protection or topical creams have been used, but are not a cure for the condition
  • Some cases of vitiligo are thought to be linked to a nutritional disorder, so ensuring your horse’s diet is properly balanced is recommended

Is Your Horse's Diet Missing Anything?

Identify gaps in your horse's nutrition program to optimize their well-being.

References

  1. Druml T. et al., Equine Vitiligo-like Depigmentation in Grey Horses Is Related to Genes Involved in Immune Response and Tumor Metastasis. BMC Vet Res. 2021. View Summary
  2. Sánchez-Guerrero M.J. et al., Genetic and Environmental Risk Factors for Vitiligo and Melanoma in Pura Raza Español Horses. Equine Vet J. 2019. View Summary
  3. Wilson D.A., Depigmentation Disorders (Vitiligo). In: Clinical Veterinary Advisor. W.B. Saunders. 2012.
  4. Fonteque J.H. et al., Vitiligo in Equine: A Four-Year Case Study of a Roan Horse ˗ Case Report. Arq. Bras. Med. Vet. Zootec. 2021.
  5. Essien K.I. and Harris J.E., Animal Models of Vitiligo: Matching the Model to the Question. Dermatologica Sinica. 2014.
  6. Day M.J., Chapter 25 – Systemic Lupus Erythematosus in Domestic Animals. In: Systemic Lupus Erythematosus (Fifth Edition). Academic Press. 2011.
  7. Tham H.L. et al., Autoimmune Diseases Affecting Skin Melanocytes in Dogs, Cats and Horses: Vitiligo and the Uveodermatological Syndrome: A Comprehensive Review. BMC Vet Res.View Summary
  8. Montes L.F. et al., Vitiligo in a Quarter Horse Filly: Clinicopathologic, Ultrastructural, and Nutritional Study. J Equine Vet Sci. 2008.
  9. McLean L.M. and Jones W.E., Depigmentation — Copper Supplement Therapy a Case Report. J Equine Vet Sci. 1983.
  10. Mozos E. et al., Focal Hypopigmentation in Horses Resembling Arabian Fading Syndrome. Equine Vet Edu. 1991.
  11. Saleh H.M.A. et al., Evaluation of Serum 25-Hydroxyvitamin D Levels in Vitiligo Patients with and without Autoimmune Diseases. Photodermatol Photoimmunol Photomed. 2013.
  12. Mahmmod Z. and Ismael D.K., Vitamin D Deficiency in Patients With Vitiligo: A Cross-Sectional Study From Basrah, Iraq. Cureus
  13. Tang L. et al., Vitamin D Protects Human Melanocytes against Oxidative Damage by Activation of Wnt/β-Catenin Signaling. Lab Invest. 2018.
  14. Karagüzel G. et al., Vitamin D Status and the Effects of Oral Vitamin D Treatment in Children with Vitiligo: A Prospective Study. Clinical Nutrition ESPEN. 2016.
  15. Watabe A. et al., Efficacy of Oral Cholecalciferol on Rhododendrol-Induced Vitiligo: A Blinded Randomized Clinical Trial. J Dermatol. 2018.
  16. Podhaisky H.-P. and Wohlrab W., Is the Photoprotective Effect of Vitamin E Based on Its Antioxidative Capacity?. J Dermatol Sci. 2002.
  17. Elgoweini M. and Nour El Din N., Response of Vitiligo to Narrowband Ultraviolet B and Oral Antioxidants. J Clin Pharmacol. 2009.
  18. Akyol M. et al., The Effects of Vitamin E on the Skin Lipid Peroxidation and the Clinical Improvement in Vitiligo Patients Treated with PUVA. Eur J Dermatol. 2002.
  19. Memon H.S. et al., Effect of Vitamin B12 and Folic Acid in Vitiligo Patients. P J M H S. 2021
  20. Tsai T.-Y. et al., Serum Homocysteine, Folate, and Vitamin B12 Levels in Patients with Vitiligo and Their Potential Roles as Disease Activity Biomarkers: A Systematic Review and Meta-Analysis. J Am Acad Dermatol. 2019.
  21. Juhlin L. and Olsson M.J., Improvement of Vitiligo after Oral Treatment with Vitamin B12 and Folic Acid and the Importance of Sun Exposure. Acta Derm Venereol. 1997.
  22. Schallreuter K.U. et al., Decreased Phenylalanine Uptake and Turnover in Patients with Vitiligo. Mol Genet Metab. 2005.
  23. Cormane R.H. et al., Phenylalanine and UVA Light for the Treatment of Vitiligo. Arch Dermatol Res. 1985.
  24. Yaghoobi R. et al., Comparison of Therapeutic Efficacy of Topical Corticosteroid and Oral Zinc Sulfate-Topical Corticosteroid Combination in the Treatment of Vitiligo Patients: A Clinical Trial. BMC Dermatol. 2011.