The most likely cause of sunburn in horses is known as photosensi t ization. Photosensitization means hypersensitivity or allergy of the skin to sunlight. With photosensitization, non-pigmented skin is at risk whenever substances in the diet and sunlight reach a certain combination level.
Unfortunately horses with sunburn are often discovered after the damage is done. Like humans, the sunburnt skin will initially appear red, and as the condition becomes more progressive and/or severe, the reddened areas blister, becoming dry and cracked. Typically the horse’s muzzle is the first to show signs of sunburn. As the sunburn progresses, other white regions on the horse’s face, legs or body become involved.
Sunburn can be extremely painful and uncomfortable which may result in horses becoming head shy.
Darker-haired horses generally do not experience sunburn. It is the fair-coloured horses, such as Appaloosas, paints, pintos, cremellos and palominos, with their pink skin and lack of pigment, whom are most affected.
Photosensitization results in sunburnt, crusty, peeling skin that dies and sloughs. It occurs when photodynamic substances circulate in the bloodstream and become deposited in the skin. Once these substances are exposed to UV light, they fluoresce, and cause oxidative damage to the cells of the skin creating the burn.
PLANT AND DRUG TRIGGERS
Tetracycline, an antibiotic, and Atravet, a tranquilizer, are two medicines known to cause photosensitization. There are also a number of plants that contain photodynamic agents responsible for photosensitization; of these plants alsike clover is the most recognized.
Rich alfalfa, red and white clover, and various weeds are also possible sources. Horses that are at the greatest risk for plant-induced photosensitivity are those that are grazing poor pastures that contain clovers and weeds. Some horses can develop a preference for a particular plant, such as these clovers and weeds, which furthers their risk for photosensitization.
Since it is not always possible to identify the offending plant responsible for the problem, owners are advised to remove the horse from the pasture, providing them with plenty of roughage and water.
Depending on the severity of the sunburn it may also be advisable to avoid exposure to intense sun, pasturing affected horses from dusk to dawn. Timely attention is necessary to minimize permanent scarring and disfigurement that can occur with serious sunburn.
Removal from sunlight will prevent further damage, after which the skin must be given time to heal. Topical products such as apple cider vinegar, aloe vera, and vitamin E gels lessen the discomfort of the sunburn and aid recovery of the skin. Susceptible horses may also benefit from the application of sunscreens as well as wearing a full-face fly mask or body sheet.
It is also important to observe sunburnt horses for signs of trouble that extend beyond the skin itself. These signs may include weight loss, appetite loss, mild colic, and diarrhea and are likely indicative of liver distress. Alsike clovers cause liver problems unique to horses. Horses with a taxed liver are particularly vulnerable to photosensitization. Additional diagnostics may be necessary to rule out liver complications.
The skin of some horses may be particularly sensitive to the chemicals found in insect repellents, grooming aids, and certain plants such as buttercup. Combined with sun exposure these substances can result in a reaction that may appear like a sunburn.
As with most conditions, early recognition and timely intervention are key to managing susceptible horses.
Carol Shwetz is a veterinarian specializing in equine practice at Westlock, Alberta.