GORDON’S FEED
HORSE SUNBURN
Prevention
and Treatment
S
ome horses are vulnerable to sun damage—even more so after
ingesting or touching certain plants. Here’s what to watch for and how
to protect against it.
Chrome. It enchants horse owners and judges alike, turning heads in the
barn and in the competition arena. Many horsemen covet and some even
breed for eye-catching white legs and facial markings, and fans ooh and
ahh about it from the stands. The flip side to flashy, however, is that the
underlying unpigmented skin is vulnerable to the sun’s ultraviolet (UV)
rays—and burn it does, becoming red, sensitive, and peeling. But these
horses’ reactions can become even more serious than sunburn, involving
localized swelling, crusty scabs, oozing blisters, and areas of severe
inflammation. These are all signs of photosensitivity, which can be brought
on by a variety of exposures.
Primary Photosensitivity
Some plants (St. John’s Wort, buckwheat, perennial ryegrass, whiteheads)
can cause skin problems when horses ingest or even touch them.
Photosensitivity is a severe dermatitis (skin inflammation) that occurs
when certain plant pigments damage nonpigmented skin cells with sun
exposure. The pigments get absorbed in the gut before passing to the skin
via the circulatory system.
Stephen White, DVM, Dipl. ACVD, professor and chief of service
in dermatology at the University of California’s School of Veterinary
Medicine, in Davis, explains that “photosensitivity in the horse is usually
caused by a photodynamic (inducing or intensifying a toxic reaction
to light) agent … in or on the skin that absorbs energy from light and
transfers it to skin cells, which ultimately destroys them.” This is known as
photosensitivity Type I, sometimes called primary -photosensitivity.
“The activating light is generally in the ultraviolet A range (320-400
nanometers),” he continues. “Melanin (pigment) in the skin screens
ultraviolet light, thereby limiting photosensitivity reactions to white and
light-colored areas of the horse’s body.”
Indeed, hair and melanin tend to block passage of light, and hairless
areas of skin, in particular those around the muzzle, ears, eyes, face,
udder, beneath the tail, and on white legs and the coronary band are most
susceptible to UV exposure. “Photosensitization in pigmented skin,” White
reports, “is not usually the case unless there is a ‘lap-over’ effect from a
nearby un- or lightly pigmented area.”
As one might expect with horses’ grazing habits, the inciting cause of
skin damage in most photosensitization cases is plant consumption.
However, “there is thought that certain plants such as clover may cause
photosensitization by contact if they are moist, as might occur in a rainy
season,” says White.
“Burning Up” continues in the June 2016 issue of The Horse: Your Guide To Equine Health
Care with detailed information on secondary photosensitization and sunburn. Subscribe
now and get a free download of this issue. Source: horsefamilymagazine.com
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