Every summer the time comes again when many horses rub their tails and manes. But not only summer eczema, in which horses are allergic to the saliva of the Culicoides mosquito, is a major problem, but also allergies in which the triggers are found throughout the year, such as mold in the hay ("hay allergy") or pollen.
With the allergies mentioned it concerns a so-called type I allergy, d.h. at some point the first contact occurred, which was still asymptomatic, and then the body forms so-called IgE antibodies. These recognize in the consequence then always an penetration of these allergens into the body and it comes to an activation of the mast cells and basophil granulocytes. During this reaction, various chemical messengers such as histamine are released, which promote an inflammatory reaction and subsequently cause itching, watery eyes, coughing or hives, i.e. the typical symptoms of an allergy.
In contrast to pollen allergy sufferers, for whom the grazing season is the more difficult season, horses with an allergy to molds from hay are usually symptom-free in the grazing season and suffer more in winter. However, not all horses that cough necessarily have an allergy behind it.
RAO or COPD is often not an allergic disease
Often horses with RAO (Recurrent Airway Syndrome) or COPD (Chronic Obstructive Bronchitis), as the condition is also called, are labeled as having hay allergies. These horses react to the dust in the hay with irritated airways, coughing and sometimes respiratory distress. In the literature, cases are described in which IgE antibodies against mites could be detected, also allergies against mold spores have been shown, but not against dust. There is no such thing as a "hay allergy", horses can only be allergic to mites or molds contained in the hay. Hay dust in itself can trigger a (non-allergic) irritable cough in horses with inflamed airways.
Ultimately, several factors can lead to COPD, starting with chronic suppuration of the paranasal sinuses, through inappropriate husbandry (for example, closed stalls with poor breathing air), to feeding errors such as moldy hay. COPD can be allergic (molds, mites, pollen, animal dander…), but it does not have to be. Here, it must first be clarified what exactly triggers the symptoms in order to be able to help the horse in a targeted manner. A diary can help to narrow down the possible causes more precisely if the occurrence and severity of the symptoms are compared, for example, with the time of year, pollen calendar, changes in posture or feed quality.
Nose nets and adapted feeding
For pollen allergy sufferers who often react with headshaking, nose scratching or nasal discharge, nasal nets have often proved useful. In addition, free access to the barn during the day is beneficial so that the horses can retreat. They are often exposed to less pollen in the stable than in the pasture or outdoors.
The situation is quite different in the case of mold allergy sufferers: these tend to benefit more from grazing in summer and avoiding exposure to molds, such as.B. Shavings bedding. Warm air dried hay. Every slightly moldy bale of hay, which is still "put away" by healthy horses, can trigger the next allergy attack, which can range from coughing to severe respiratory episodes.
For summer eczema sufferers, an eczema blanket is usually indicated, unless you live in coastal regions or at altitudes where the allergy-causing mosquitoes are not present. In the case of sweet itch, the presence of KPU should also be clarified and the feeding adapted. The more sugar these horses are fed, the more attractive they are to mosquitoes. Therefore, feeding can have a considerable influence on the occurrence and severity of the allergy.
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Congenital allergy in horses
Especially with Icelandic horses, it is often discussed whether their allergy to the saliva of the Culicoides mosquito could also be congenital and therefore a certain genetic predisposition could be found within the lines or the breed. Pedigree could be detected. Unfortunately, however, no definite "sweet itch gene" has been found to date.
In addition, environmental factors play just as large a role in allergies as genetics.
As far as is known today from studies on various animal species, several genes are usually involved in the development of allergies, so that identification is not so easy and affected animals cannot simply be excluded from breeding. In addition, as already mentioned above, epigenetics also plays a very important role in allergies, because not always when z.B. a certain mutation in a gene is present, it also means that this must lead to clinical symptoms.
Even if one day there should be a "gene test" for sweet itch, this does not say 100% whether the horse will also suffer from it. For the time being, such genes only speak for a predisposition, i.e. a predisposition for a certain disease or sensitivity. Whether this disease will break out and become clinically relevant or not, depends among other things on the living conditions such as feeding, husbandry, medication, stress level etc.. from. For the allergy-plagued horse, this is of little use at first. The exact cause is much more helpful, because then you know which allergens you should avoid.
Allergy tests for horses
In the meantime, there are several allergy tests for horses. In most commonly used so-called ELISAs (Enzyme Linked Immuno Absorbance Assay), the IgE antibodies are detected in the serum. However, these are not yet sensitive enough to be able to make a reliable statement. Here false negative as well as false positive results can occur. This means that substances can be recognized as problematic allergens without the horse showing symptoms (false positive) or that substances are not recognized as allergens although the horse reacts to them with allergic symptoms (false negative).
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Assays that measure the leukotriene content of basophil granulocytes (CAST- cellular antigen stimulation test) or the histamine content (FIT- functional in vitro test) are more suitable. The greatest difficulty is always to identify the exact allergen.
If this were to be successful and the triggering factors were known, then desensitization via immunotherapy in horses would also be more successful. At present, however, the success of desensitization in horses is very limited. A good management of the allergic horse has usually more effects on the quality of life than such treatments.
Immunotherapy in horses
Currently, the greatest hope in the treatment of allergies in horses is placed in immunotherapy. Here, however, research is still in its infancy. Most publications report an improvement of the symptoms in the first two years, which then decreases again. More reliable tests that identify the exact antigen and a targeted immunotherapy based on this would be desirable, but are (unfortunately) still dreams of the future. Until then, the only thing left to do is to manage the horse with appropriate husbandry and feeding measures so that it can cope with it as well as possible.
Allergy prevention and management
The less stress a horse is under and the fewer feeding mistakes are made, the lower the risk that an allergy will develop in the first place. If the intestine is not in order, the allergy susceptibility increases significantly, since about 70% of the horse's immune system is located in the intestine. Inflammation of the intestinal mucosa and the associated "leaky gut syndrome" cause an overload of the immune system located in the intestinal wall. Even if the horse does not (yet) show any symptoms of an allergy, it is possible to preventively avoid feeds that promote the development of an allergy, e.g.B. Haylage.
But stress can also lead to chronic inflammatory reactions in the gut, only it is often very difficult to detect in horses. Here, for example, chronic pain or unsuitable housing conditions can be the trigger. Not every horse is suitable for group housing, especially old or low-ranking horses are often under constant stress in large groups or in herds with frequent changes. Chronic pain, for example, from arthritis, subclinical laminitis, or because horses have to stand on hard ground all day in turnout, for example, can also be problematic. In the long term, they not only cause stomach ulcers, but also intestinal mucosa inflammations, which in turn increase the susceptibility to allergies.
Of course, all these factors are also valid if the horse already suffers from an allergy. Through stress reduction. Avoidance of feeding errors or.