Allergies such as sweet itch, recurrent airway obstruction, urticaria and atopy are not uncommon in horses but they are frequently difficult to diagnose and can be frustrating to treat.
The horse’s immune system is highly complicated and normally very effective at eliminating potentially dangerous threats, such as viruses, bacteria or parasites. An allergy is an adverse or strongly exaggerated reaction of the immune system to something (an allergen) that is usually harmless, resulting in adverse effects that are not of any benefit to the animal. The reaction may be local (confined to one area) or systemic, which means the changes can be seen across various body systems.
Horses can suffer an allergic reaction at any age and can develop an allergy at any time. Allergies may be triggered by a biological substance with a protein that can be recognized by the immune system. This typically includes substances such as pollens, moulds, spores, insect bites, certain foods and drugs. There are different forms of allergy and different symptoms that are well recognised. However, some are less easy to diagnose, especially when the symptoms are subtle, intermittent or atypical.
Some allergic reactions are acute in onset, while others develop over a period of months or years. Either way, your vet can talk you through the most important steps to settle the changes you are seeing and advise whether an urgent visit is necessary. If your horse does require veterinary attention, the first step will be to try to accurately identify the true causative allergen. Depending on the signs and symptoms, the nature of the problem may be fairly apparent or may require further diagnostic testing.