When equine skin gets itchy, it can be puzzling to figure out what’s causing it, much less how to treat it.
Glen Hecox didn’t know what was going on with his red roan yearling gelding, Pepper. Hecox first noticed the young Quarter Horse—out on pasture with the broodmares—scratching his back on a low tree branch, but as spring came on the itching seemed to suddenly escalate.
“He started rubbing his shoulders, his tail, his neck, whatever he could reach,” Hecox recalls. “He rubbed until the hair was gone.”
On first examination, Sonny Seale, DVM, of Garner Equine in Weatherford, Texas, suspected one thing behind Pepper’s problem: atopic dermatitis, also known as “atopy,” or skin allergies.
Allergies in horses can show up as a variety of responses, from an anaphylactic reaction—such as an allergic reaction to an injection of penicillin or another drug—to respiratory problems like heaves. But one of the most common responses is through the skin.
“Humans demonstrate most of their allergies through their mucous membranes,” Seale explains. “So when you are allergic, your nose runs and your eyes itch and swell. But horses typically demonstrate allergies through their skin.”
The horse comes into contact with an environmental allergen—such as a pollen, dust or mold—and the skin reacts, causing the horse to itch. And then itch more.
“There is a pattern to it,” Seale says. “The atopy tends to be focused initially in the mane and on the tail head. You’ll get roughening, breakage and hair loss. As the condition worsens, it’ll progress to the face, shoulders and across the body. Patches of the skin will get a roughened, grayish, elephant-hide appearance.”
Secondary irritations can result from open sores and abrasions, he says, caused by self-trauma from scratching, and those can become infected, as well.
“[In North America] the condition typically shows up April through November, and progresses through those months,” he says. “Some years will be worse than others depending on variations in the pollen count, weather conditions and the [individual] horse. Usually you’ll see the mild itching first, and then hair loss and abrasions. That [progression] can happen in days or weeks, or over many months.
“It’s extremely variable. Every horse responds differently and conditions can change from season to season and year to year.”
Atopy can show up in horses of all ages, Seale says, and he has seen it run in families, indicating a genetic predisposition. Left untreated, it only gets worse as the horse ages.
Luckily, Pepper didn’t progress to secondary skin lesions. Hecox later noticed the itching eased off when the winter months rolled back around, and the hair grew back on the gelding’s mane, tail head and shoulders.
Even though Pepper’s condition followed the atopy pattern, Seale took steps to rule out other potential causes of his itchiness.
“A lot of skin conditions can look alike,” Seale warns, “so you have to do your due diligence in a physical exam and history, and rule out parasites or irritants that could be behind it.
“We also did a thyroid test on this horse, because hypothyroidism can contribute to skin conditions, but his was functioning correctly.”
There are two ways to test for allergies, Seale says: an intradermal allergy test, also called a skin sensitivity “scratch” test, or a serum allergy test via blood sample.
“Skin sensitivity testing is probably the ‘gold standard’ test for allergens, because it’s more specific,” he says. “You shave the skin on the side of the neck and inject small quantities of different antigens [allergic reaction-causing agents] and measure the reaction, or wheal, each causes on the skin.”
However, it’s not a practical way to test for the hundreds of allergens that could be in a horse’s environment.
“I’ve gravitated to and had better luck with the blood test, because of the number of allergens I could test for,” he says. “There are companies that offer regional blood testing with different allergen panels. So, for Texas and the Southwest, the panel would test for what grows here—grasses, weeds, molds, and specific insect sensitivities—and for what is typically blown in here according to our wind patterns.”
Every panel also tests for allergens found in every horse’s environment, he adds, such as foods, insecticides, or mouse and cat skin cells.
Pepper tested allergic to 30 different allergens that included regional trees such as mesquite, cedar and oak, nine different grasses, as well as various weeds, insects and molds. His one food allergy was molasses.
Treating to Cure
Environmental and medical treatment strategies for allergies vary from horse to horse. An insect allergy can be helped with fly sheets, repellents and fly mitigation in the barn. Shampoos and conditioners that contain antihistamines, as well as topical corticosteroid ointments, can ease itchy skin. A diet can be altered to accommodate a feed allergy, and an environmental change—such as feeding hay on the ground versus in a confined trough—can reduce a horse’s inhalation of dust allergens.
In Pepper’s case, Seale recommended allergen-specific immunotherapy through hyposensitization injections. The goal is to gradually induce the horse’s system to become immune or no longer responsive to the allergens.
Once a horse’s individual allergen panel is established, the hyposensitization injections can be ordered to match it.
“Treatment consists of injecting increasing concentrations of these antigens over time,” Seale explains. “Initially, you inject a couple of times a week, then you go to once a week, then every other week and then once a month.”
When it works, it’s a cure. But it can take a long time. In Pepper’s case, it took four years of monthly hyposensitization injections to cure his allergies.
“It’s an anecdotal estimate, but I’d say we’ve gotten an 85 percent success rate in curing allergies by treating with these hyposensitization shots alone,” Seale says. “The shots can take horses from constantly needing to be on steroids or antihistamines to relieve the allergy to just giving them one steroid shot a year if they are also receiving immunotherapy.
“In my experience, the ones we’ve had a lack of or limited success with have had a shifting allergy profile,” he adds. “We might get a year or two of control of the atopy, and then owners will report that [the immunotherapy] is not working any longer. We’ll test them again and find that the allergens that they were originally sensitive to are now negative. We’ve cured those allergies but they have seven new allergens they’re positive to that they weren’t before.”
Hecox eventually sold Pepper to a team roper, with full disclosure of his allergies and his medical history. At that time he no longer needed the hyposensitization shots. As far as Hecox knows, the horse is doing fine.
“I’m pretty sure it was genetic, and his mother passed it on to him,” Hecox says.
Of the mare’s four foals, only Pepper and a half-sibling by a different sire had the allergies show up when they were yearlings. Oddly enough, Pepper’s full sibling never showed signs of having allergies.
“The mare has since died,” Hecox says. “I kept her fourth foal, a filly, that had never showed signs of the condition. But I don’t think I’d have bred that mare again.”
This article was originally published in May 2017 issue of Western Horseman.