What are these lumps?

Equine Allergies

Has your horse ever suddenly developed fluid-filled lumps all over their body? If they have, you may know that this is called ‘Urticaria’ or ‘Hives’ and that it is an allergic response to allergens.
An allergy is simply an exaggerated response from the immune system to a substance in the environment. Allergic reactions are extremely common in horses, whose immune systems can overreact or become hypersensitive to things they touch, inhale, eat, or that are injected into them.
The two most common allergic conditions that we see in horses are related to the skin; urticaria, and the respiratory system; Equine Asthma.
Allergies in horses are thought to be cumulative, meaning a horse can be allergic to several things but it is the combination of separate allergies finally reaching the individual’s limit or threshold that causes outward signs to appear.

How do I know if my horse has allergies?

Hives (urticaria) and intense itching (pruritus) of the skin, and/or coughing and nasal discharge, are the most frequent symptoms of allergies in horses. Hives are fluid-filled, raised swellings or wheals on the skin, which can appear minutes to days after exposure, may or may not be itchy, and can show up nearly anywhere on a horse’s body. When itching, scratching, and rubbing are the main signs of a skin allergy, the pattern of distribution on the body, time of year, and geographic location are helpful clues as to the underlying cause.
Respiratory allergies in horses can present in several ways. The first is known as allergic rhinitis or rhinoconjunctivitis. Horses with this condition will present with a runny nose as well as red, swollen, and watery eyes. The other is the more complex condition is known as ‘Equine Asthma’, previously known as Inflammatory Airway Disease (IAD). Equine asthma is often caused by substances that trigger an allergic response. Coughing, nasal discharge, and increased breathing efforts are common signs of this condition.

Common Causes

The most common cause of urticaria is thought to be insect hypersensitivity as well as the most common reason for horses to itch. While horses can be allergic to many different insects, such as march flies and stable flies, the biting midge (Culicoides) appears to be one of the main culprits for causing an allergic response.
Horses housed in conventional stables with high levels of airborne particles (dust, pollen, fungi, moulds, ultrafine particles, and noxious gases such as ammonia (from urine) are more at risk of developing equine asthma. Dust from feed is also a major source of allergens. Having said this, horses that live in outdoor areas can also suffer from this condition, depending on their level of sensitivity.
The list of known allergens for horses is exhaustive, and may include insect and mite debris, fungi, molds, vegetative material such as pollens, and noxious gases like ammonia. Dry hay and dusty bedding are responsible for most of the particulate matter getting into the horse’s airway.

Diagnosis

Like most conditions, allergies are diagnosed by a combination of history, signalment and clinical signs. Further tests such as skin scrapings and cultures may be used to rule out infections or ectoparasitic infections. With respiratory cases, endoscopic examination and a Bronchoalveolar Lavage (BAL) may be conducted.
Once the evidence points to allergies as the culprit, medication can be commenced. Dexamethasone, or prednisolone are commonly used anti-inflammatory drugs as they are very good at suppressing the immune response. Antihistamines are also commonly used. In the case of chronic allergic reactions, or where it is important to know the specific cause, specialized allergy testing can be performed to confirm the diagnosis to assist with a treatment plan.