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.
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:
- Lipizzaner
- Andalusian
- Gelderlands
- Shires [3]
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.
Equine 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.
A 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 hors