One condition that is often
overlooked in healthcare for your paint horse is photo-sensitization. Photo-sensitization
is a common problem in horses with pink or non -pigmented skin, such as paint
horses, but can occur in any horse. The horse’s skin reacts to natural sunlight
when photodynamic substances have accumulated in and traveled through the
bloodstream. These hotodynamic substances are activated via ultraviolet light
exposure and cause the horse to exhibit a severe hyper-allergenic immune
reaction.
Certain plants, such as alsike
clover, ragwort, St. John's
Wort and buckwheat contain chemicals that contribute to photosensitization.
Therefore, horses eating these forages may experience minor reactions. Horses
with liver disease cannot adequately filter chlorophyll; therefore, this group
may also be more susceptible to photo-sensitization reactions.
Obvious signs of photo-sensitization
are usually ob-served on areas with little or no pigmentation (white legs and
muzzles). In minor conditions, these areas will be slightly swollen with urticaria
(hives) and may be pruritic (itching). It is important to note that true photo-sensitization
is more severe than general sunburns. A horse with sunburn would have minor
reddening of the skin and some scabbing. A horse experiencing photo-sensitization
will have more severe dermatitis characterized by scabbing, ulcerative sores
and dermal vasculitis. In more severe cases extreme cyanosis (blue or purple
coloration of the skin) is followed by swelling, blistering, and skin cracking
appears to resemble a chemical burn. Skin will appear to “leak” serum, or a
yellowish fluid.
The most effective prevention
against photo-sensitization is to keep susceptible horses away from high-legume
pastures in fall and spring. Other prevention measures include keeping horses
out of natural sunlight and in dark areas until any pharmaceuticals have been
eliminated from their system. Treatments include administration of
corticosteroids, pharmaceutical pain management, and topical applications.
Topically, areas of affected skin can be treated with sun block products, and/or
cooling salves such as diaper rash ointment (used for humans) which is comprised
predominantly of zinc oxide.
Thank you to Dr. Kimberly
I. Tumlin for this article.
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