Investigation highlights just how little we know about allergies in horses


Evidence of adverse food reactions in horses is largely anecdotal, a wide-ranging position paper has found.

Foods found to be associated with adverse food reactions in horses anecdotally include potatoes, malt, beet pulp, buckwheat, fish meal, wheat, alfalfa, red clover, white clover, St John’s wort, chicory, barley, and oats.

The Messerli Research Institute, a joint venture between the University of Veterinary Medicine Vienna and the Medical University of Vienna, has condensed the knowledge about human and animal food allergies and intolerances into a just-published European position paper.

The paper, published in the journal Allergy, highlights the strong similarities between animal and human symptoms and the triggers for adverse food reactions.

It sums up food intolerances and allergies in both animals and humans, laying bare major knowledge gaps.

The authors stressed the need for more comparative studies on the mechanisms and the diagnosis of food intolerance, and on formulating adequate measures.

It found that people were not the only animals suffering from the symptoms and problems of food intolerance and allergies. Other mammals, such as cats, dogs and horses, are affected as well.

“Not only humans but basically all mammals are susceptible to developing allergies, as their immune system is capable of producing immunoglobulin E,” lead author Isabella Pali-Schöll said.

Normally, these special antibodies help defend against parasites or viruses. At the same time, they are also responsible for some allergy symptoms, which include hay fever, allergic asthma and anaphylactic shock.

In the field of nutrition, there are also very common non-immunologic forms of food intolerance.

The position paper, primarily penned by Pali-Schöll and her Messerli colleague Erika Jensen-Jarolim, shows that the symptoms of food intolerance are similar in both animals and humans.

However, in the case of horses, dogs, or cats, adverse reactions mostly affect the skin, followed by the gastrointestinal tract.

“Asthma or severe shock reactions have rarely been observed in animals,” notes Pali-Schöll, who is a nutrition scientist.

There are even overlaps among the triggers of immune response to certain foods and ingredients. Pets may suffer from both lactose intolerance and outright milk protein allergies. Some mammals are also liable to suffer allergic reactions from certain proteins in wheat, soy, peanuts, tree nuts, fish, eggs and meat.

Diagnostics limited

The paper noted that molecular-based allergy diagnostics for animals remained underdeveloped. Many mechanisms and triggers for animals have not been sufficiently researched, in part because some test samples or substances were not even available.

Avoiding allergens was the best that animals and people could do for now, Pali-Schöll and her colleagues found.

A so-called elimination diet is the prerequisite for correctly diagnosing animals and humans. This involves removing all sources of protein from an animal’s diet.

“During this period of diagnosis, the animal will be fed homemade food or diet food prescribed by a veterinarian. Only then, and if there have not been any dangerous allergic reactions before, can ‘normal’ food be gradually reintroduced,” Pali-Schöll says.

This diagnostic procedure allows the allergen-free diet to be tailored to the respective food intolerance, while avoiding unnecessary restrictions.

A thorough comparison of adverse food reactions in humans and animals offers insight into the risk factors for the development of the condition, and can thus lead to improved recommendations for the prevention and treatment of adverse food reactions in animals and humans.

At the moment there are no therapies for humans and animals, but many new variants of immunotherapy have entered trial phase.

The authors said the true prevalence of food allergy in dogs, cats, and horses was unknown.

In dogs with clinical signs suggestive of allergic dermatitis, the prevalence of adverse food reactions was reported in research to range between 7.6% and 25%. In another study, it was diagnosed in 1.69% of the total dog population presented to a veterinary teaching hospital over 12 months.

The prevalence in cats ranged from 0.22% to 6% of animals with skin signs and from 17% to 22% with gastrointestinal tract signs.

“In horses, there is only anecdotal evidence with few cases documented in peer-reviewed literature,” they said. “Possibly, the condition is underdiagnosed or corrected by owners prior to seeking veterinary attention.”

The researchers further noted that the mechanism of food allergy was unknown in the horse. Skin-related reactions had been noted in horses, as had respiratory signs.

“Food-specific immunoglobulin E (IgE) has been found in horses with allergic skin disease, and positive intradermal testing (IDT) reactions to food occur in allergic horses.

“However, both IDT and serum IgE frequently give false-positive reactions in clinically healthy horses and do not correlate well with symptoms. Thus, a definitive diagnosis of food allergy in horses can only be confirmed by elimination trial,” they wrote.

Allergy is the European journal of allergy and clinical immunology.

Comparing immediate-type food allergy in humans and companion animals — revealing unmet needs
I. Pali-Scholl, M. De Lucia, H. Jackson, J. Janda, R. S. Mueller, E. Jensen-Jarolim.
DOI: 10.1111/all.13179

The paper, published under a Creative Commons License, can be read here



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