Spring allergies tend to strike horses as soon as the weather begins to warm. With any allergy, a horse becomes sensitized to the offender - usually a protein of some sort. While initial contact may not cause any obvious problem, repeated exposures lead to reactions that can be most easily described as "over-reaction" by the immune system with release of histamines.
Spring allergies tend to strike horses as soon as the weather begins to warm resulting in the immune system releasing histamines that lead to rashs, hives, and sores.
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Horses with skin allergies will itch, bite, rub, and roll to relieve the irritated area. Common causes of skin allergies in horse are insect bites. The Culicoides species of biting midges, or "no seeums," are first on the list of irritating insects, but horses can be allergic to virtually any biting insect.
Insect saliva sets off an immune reaction and your horse may develop hives or weeping sores, especially on the midline of his stomach. Rubbing and rolling irritate the areas even more.
You may hear the terms "summer itch," "sweet itch," or "Queensland itch" used to refer to allergic reaction to Culicoides species' saliva. This is not just an Australian phenomenon, but can occur in horses in almost any geographic area.
Parts of the body most affected tend to be around the mane, tail, and the top of the back. Some horses also show signs of pruritus near the head and ears.
According to Lydia F. Gray, DVM MA, writing for SmartPak, "Several research studies have shown that supplementing horses with omega-3 fatty acids—such as those found in flax seed, chia seed and fish oil—actually reduces inflammation in the body. One study specifically looked at horses with “sweet itch” and found a significant decrease in allergic skin response when they were fed flax seed."
Dr. Gray also suggests, "While the benefits of omega-3 fatty acids are many and definitely include supporting skin health, MSM is another supplement you may want to consider for your horse. This potent antioxidant also has research supporting its use in allergic conditions, specifically recurrent airway obstruction or “heaves.” It is also reported to support the immune system as well as resilient skin, coat and hooves."