Horse Allergy Symptoms
The most common symptoms of horse skin allergies manifest as rashes known as hives or urticaria. Hives can occur on any part of the epidermis. Horses with urticaria frequently exhibit allergic reactions to inhaled pollens, as well as to the bites of insects, including flies (horse, stable, caddis, house and deer fly), mosquito, and the biting midge known as Culicoides.
Hives can be highly pruritic (itchy), and can last from a few hours to several days or weeks. Self-trauma lesions and secondary infections may follow. Other symptoms can include subcutaneous edema, especially around the head and eyes. (Lewis, LD. 1995)
Also known as “summer eczema,” this is an allergic reaction to the saliva of the biting midge (Culicoides). It is characterized by papules that frequently result in scabs, localized at the base of the tail, dorsum, and base of the mane and ears.
The severe itching caused by these lesions, and the subsequent rubbing to obtain relief, results in hair loss and thickened/scaly skin.
Respiratory Symptoms – Recurrent Airway Obstruction (formerly COPD)
A more complex allergy in horses is an inflammatory lung condition known as Recurrent Airway Obstruction (RAO), formerly called Chronic Obstructive Pulmonary Disease (COPD). RAO-associated inflammation in the airway causes breathing to become labored. The horse must expend a considerable amount of effort to expel air from the lungs leading to your horse coughing or dry-heaving.
RAO is the equine equivalent of human asthma. Heavy horses have an increased respiratory rate, often using the abdominal muscles to help move air which can cause them to be underweight due to the extra exertion. Molds and fungal spores found in barn dust and hay feed are the main contributors to RAO.
In temperate areas of the world where horses spend most of their time in warm pastures, a variant of RAO known as “summer pasture heaves” occurs in susceptible animals. Grass or hay pollens and molds associated with damp pasture forage are the causative allergens in this disease.
Both IgE-mediated and delayed type hypersensitivities contribute to RAO. Cellular infiltration into the lung causes increased mucus production and subsequent narrowing of the airways.
Respiratory allergies in horses can also contribute to head shaking, sneezing and chronic nasal discharge in some horses.