The easiest way to think of allergies is as an immune reaction that gets carried away. The immune system is programmed to react to every foreign substance that enters the body. Invading bacteria, viruses and fungi are top targets, but drugs, pollens and even food can trigger a reaction.
If an individual is unlucky enough to be exposed to a sufficient amount of an allergen while recovering from a respiratory infection that weakened respiratory-tract mucosal linings, that allergen has the opening to contact local tissues and produce an immune/allergic reaction. Similarly, if complex foods are given to a young animal before the gut has developed sufficiently to handle it — or to an animal of any age that has inflammation/irritation of the intestinal tract — the stage is set for a food allergy.
The body reacts to allergens similarly to the way it reacts to infectious organisms — with an immediate response and a delayed antibody response. The immediate reaction is characterized by a dramatic response within 15 minutes of exposure. Things like wheezing, acute bronchospasm, heat and swelling/edema of the skin, swelling of the eyes, mouth, lips and tongue are immediate allergic reactions. Hives, skin breakdown, COPD/heaves, intestinal symptoms of food allergies are more likely to be delayed reactions.
Perhaps the most well-known example of allergic disease in horses is COPD or “heaves.” In advanced stages, the lungs are severely damaged and normal air exchange no longer possible. The horse breathes abnormally all the time and develops that classic “heave line” along the curve of the ribs from working so hard to breathe. At this point the disease is most similar to human emphysema. However, early equine COPD parallels asthma or reactive airway disease in people.
Heaves has components of both immediate hypersensitivity — triggers that will make the horse’s lungs “shut down” within minutes of breathing them in — and delayed hypersensitivity, which is responsible for the damage to the lung tissue.
Allergic symptoms in the upper-respiratory tract may manifest themselves as sneezing/snorting, increased amounts of clear to faintly white and frothy nasal discharge and cough. Exercise typically makes the symptoms worse as heavy breathing further irritates inflamed tissues. Not surprisingly, these horses are among the most sensitive to nonspecific irritants such as dust, ammonia and chemical sprays.
Unfortunately, low-grade, clear-to-frothy nasal discharges, either with or without exercise, are so common in stabled horses they may be considered “normal.” This early symptom of upper-airway irritation/allergy often worsens in the winter when the horses are outside less and barns are closed up tighter. While this discharge alone isn’t a significant problem, it can indicate that the same low-grade inflammatory reaction is in the lungs. The sooner you control it, the better chance of avoiding permanent lung damage.
Start with a well-ventilated barn. Cross ventilation through windows or via fans placed above the level of the horses’ heads can be maintained year round without direct drafts on the animals. If this isn’t possible, at least crack doors to encourage air movement and always remove the horses from the stalls, if not the barn, while cleaning and shaking out new bedding. Avoid straw bedding by switching to shavings or one of the new alternative beddings (see August 2001). Molds, dusts and microorganisms in bedding are offenders.
Dunk hay in a bucket of water before feeding or shake it out thoroughly, a small amount at a time, to remove as much dust as possible. You can also switch to hay cubes, soaking them, too, if necessary although cubes have a lower level of dust and molds.
Pay careful attention to nutrition, especially levels of key trace anti-oxidant minerals and magnesium (see minerals September 2001). The horse should receive adequate levels of vitamins E and C.
Supplements such as grape-seed extract (Uckele Health and Nutrition 800/366-8986 or www.uckele.com and MedVet 800/328-6652 or www.unitedvetequine.com) and citrus bioflavinoids (Hesperidin Complex from Uckele or HemoCease from Peak Performance 800/944-1984 or www.peakperformancenutrients.com) also help control allergic inflammatory responses. Herbal immune-stimulating or modulating supplements also help many of these horses and assist with the elimination of either chronic or secondary bacterial and viral infections.
Allergy testing and a desensitization injection series (“allergy shots”) would work for these early allergy cases, as is used in people to control allergic upper-airway problems. However, it may not be worth the bother and expense for minor problems. We would definitely consider it if the horse develops a cough or any evidence of an abnormally elevated respiratory rate during work or poor recovery to normal respirations after work.
A horse that has obvious COPD/heaves is definitely a candidate for allergy testing and desensitization. Although the effectiveness of this approach is limited by the nature of allergy tests themselves, for most horses it offers the best results in terms of long-term control and avoids the need for regular medications.
Antihistamines are often prescribed somewhere along the line. While they may help, we think they’re a better preventative than a treatment, and even then, many horses will have acute flare-ups anyway.
Any horse suffering an acute worsening of COPD warrants a call to the vet. If you know your horse has this problem, discuss with your vet the advisability of keeping medications on hand for emergency use (e.g. epinephrine, steroids or inhaled medications if you have the necessary equipment).
Always remove the horse from the environment he was in when the attack was triggered. If he was outside, bring him into the barn and put him into an area that has been lightly misted with water to settle any fine dust particles. If he was in the barn, move him outside to a quiet location.
Clean out his nostrils with a damp cloth so that breathing is unimpaired and to remove any dirt/dust. It also helps to apply a layer of camphorated rub, such as Vicks or a generic equivalent, around the nostrils (not in them). These vapors will immediately begin to thin mucus secretions so that they can be more easily moved.
Give any emergency meds you have on hand as per your veterinarian’s instructions, but don’t use any human products without getting clearance and dosage instructions from the veterinarian.
Sometimes called sweet itch or sweet bumps, the basic symptom is hives. This reaction is often blamed on sweet feed. While food-related allergies can indeed produce hives (and itching), the usual cause is hypersensitivity to biting insects. It’s no coincidence that sweet itch almost exclusively occurs in the summer months, when those flies and “no-see-ums” are at their worst. A food-related allergy is rarely seasonal.
Stress also seems to be a risk factor for sweet itch, whether food or insect-bite related. Persistent hives of this sort are most commonly reported in high-performance horses. This may be due to a need for increased levels of specific antioxidant minerals/vitamins in stressed horses, especially in cases that become chronic and poorly responsive to treatment (see hives case history at end of story).
Although hives look terrible, in and of themselves they aren’t an emergency. However, the horse must be watched closely for abnormal breathing as a consequence of the allergic reaction. Horses that are itchy need quick relief to prevent them from damaging their skin by rubbing. A long, cool bath, preferably with a tea-tree-oil-based shampoo (we like Animal Legends Leuca Lather 800/399-7387), will soothe the skin and remove any irritants.
The horse should be stabled until the hives subside to prevent any further insect bites, by far the most common cause of hives. Insect repellents should be used religiously on these horses. Application of human 1% cortisone creams or Gold Balm cream (both available in drug-store chains) helps control inflammation and itching. When there is open skin, or the hives don’t improve, you should contact your veterinarian.
The possibility of food allergies has never been investigated in any depth in horses, although it almost certainly exists. Food allergy in people and small animals most commonly takes the form of itching or other skin symptoms, such as eczema or, possibly, hives. The range of potential food-allergy-related reactions also includes lung/breathing symptoms (rare, unless it is with an immediate anaphylactic reaction) and gastrointestinal symptoms.
Gastrointestinal symptoms in humans and small animals include cramping, increased gas production and diarrhea. Diarrhea is less likely in the horse since the large intestine is more developed and can remove excess water from the stool more efficiently. However, mild cramping, bloating and increased intestinal gas are likely to occur.
It can be difficult to distinguish between a true allergy, an intolerance and simply poor breakdown of specific foods due to their being introduced too rapidly and the microorganisms in the gut not having sufficient time to adapt. Symptoms would be the same in all cases.
Feed ingredients commonly associated with allergy-like/intolerance symptoms in horses include yeast, alfalfa, soy, grains of all types, molds and unaccustomed protein sources such as blood meal, fish meal or seed meals. Concentrate mixes that aren’t fixed-formula — meaning the same ingredients are used in every batch — are often prime offenders as they tend to often change protein sources.
When feed-related allergies are suspected, diagnosis poses a real challenge. Responses to skin-testing methods and results of RAST testing aren’t terribly reliable (see sidebar on allergy testing at end of story) because food allergies may be of the delayed-hypersensitivity type rather than immediate reactions.
The best diagnostic methods are elimination diets and test meals. In elimination diets, the animal is put on a simplified diet that doesn’t include any of the ingredients thought to be possible causes. If symptoms go away, a food-related problem is suspected.
The next step is to “challenge” by adding back in the possible offending ingredients one at a time, to see if one triggers a reaction.
When food allergies are suspected because of bloating, changes in manure and increased gas, it’s often worth a try to rule out poor digestion as a cause rather than actual allergy/sensitivity. We suggest high-dose Ration Plus (800/728-4667), 10 cc twice a day for four days, then once a day for four days to see if this takes care of the problem.
If this doesn’t work, or if the symptom is skin bumps, proceed to an elimination diet. Since most of the likely offenders will be found in the grain mix, this is usually the first thing to be cut. Allow four to seven days off the grain for symptoms to resolve. If they do, start refeeding with plain grains, usually beginning with oats, and adding one at a time at four- to seven-day intervals to make sure these are not a problem.
If well tolerated, you can switch to a commercial mix that uses different processing methods for soy (check the ingredients label, it will state if the soy was cooked, roasted, dehulled, etc.) and/or avoids ingredients like brewer’s byproducts. Check with the manufacturer to be sure the grain mix is fixed-formula.
If the problem persists on hay only, the horse may be sensitive to that type of hay, contaminating pesticide or herbicide or to one of several molds that may be growing in it — not necessarily in amounts that you could detect. Changing your feed supplier may help.
Finding a steady source of organically grown hay, consistently cut at the same growth stage, is also an option but may be difficult to do. Ontario Dehy (877/289-3349 or www.ontariodehy.com) sells a certified organic, consistent-quality, alfalfa or timothy and has a good U.S. distributor network. You could also try a trial of hay cubes from a reputable major supplier to your area, such as Montana Pride, Triple Crown, Agway or Southern States. We find the bagged, chopped forage products from Triple Crown (800/451-9916 or www.triplecrownfeed.com) also work well.
The first step in treatment of an allergy is to minimize exposure to the allergen. Since complete avoidance of many common allergens is virtually impossible, desensitization injections are often recommended and are extremely helpful to most horses. Effectiveness, of course, largely depends on how carefully the triggering allergens are identified.
For flare-ups, corticosteroids are the drug of choice when rapid control is needed. Antihistamines work best as preventatives rather than a therapy, although they may be suggested. Specific bronchodilator drugs and various inhaled medications are often used for horses with COPD. For skin-related flare-ups, bathe the horse and work to be sure he is comfortable and avoids rubbing.
Also With This Article
Click here to view ”Is Your Horse Allergic'”
Click here to view ”Allergy Investigation: Case Histories.”
Click here to view ”Determining The Cause.”
Click here to view ”Nutritional Rescues.”