The Magazine May 2018

Equine allergies explained

Posted 3rd April 2018

Allergies in horses are common and they can be particularly frustrating to treat, as vet Nancy Homewood, from Hook Norton Veterinary Group, explains

An allergy occurs when your horse’s immune system overreacts to commonly found, normally harmless substances in his environment, which are known as allergens. An allergic reaction in horses can be triggered by allergens such as…

  • tree, grass and weed pollens
  • mites such as dust and forage mites
  • organic dust such as that found in hay and bedding
  • insects such as mites, flies and lice
  • certain types of food

Allergies can be frustrating because it’s often impossible to determine the underlying cause, which makes it very difficult to treat affected horses effectively.

Point of contact

Your horse can come into contact with an allergen through…

  • direct skin contact For example, with bedding, plants, items such as numnahs and rugs that have been washed in a particular detergent, or topical shampoos
  • inhalation of allergens in the environment. For example, dust, fungal spores and moulds that are commonly found inside a stable, or grass and flower pollens
  • ingestion of a particular food material. Cereals, roughage feeds and certain types of grass have all been shown to cause allergies in horses
  • insect bites The Culicoides midge is the most common cause of insect bite reactions in horses, causing sweet itch. This is an allergy to the saliva of the midge. Abnormal reactions to other insects are possible, but less common
  • veterinary treatment Allergic reactions to drugs can occur, although they’re uncommon

Signs of irritation

The signs of an allergy depend on which body system is affected, but the most common include…

  • respiratory problems, such as nasal discharge, a cough, exercise intolerance and slow recovery after work, flared nostrils at rest, raised respiratory rate and increased effort to breathe. These signs are normally caused by recurrent airway obstruction (RAO), which is an allergy to dust and mould spores, or summer pasture associated obstructive pulmonary disease (SPAOPD), which is an allergic reaction to pollen.
  • urticaria, which is the most common skin reaction in horses. Oval-shaped, fluid-filled lumps appear on the skin, which can vary in size from small, pea-sized lumps to much larger, widespread ones. They’re usually seen on the neck, chest and abdomen, but in severe cases can occur all over the body. Horses are often unaware they have urticaria, although the lumps are sometimes itchy. If the reaction is severe, serum can ooze from the lumps.

Find out more about equine allergies in the May issue of Horse&Rider, on sale 5 April.

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