Allergic Disease in Horses

It is allergy – what next?

Having reached a clinical diagnosis of allergy your vet may recommend a blood test to try and identify the specific allergens which are affecting your horse.

allervet® is an allergy test designed especially for veterinary use, a small blood sample is all that is required. The test is able to detect antibodies (IgE) against a variety of environmental and insects allergens which may be the underlying cause of your horses problems.

If your vet suspects an adverse food reaction an allervet® food test can be helpful.

Allergen avoidance can be an effective form of management and should always be attempted. If your horse tests positive for pollen antibodies, allervet® will provide illustrations of the offending plants to help you to identify and attempt to avoid them.

If sweet itch is diagnosed your vet will be able to discuss the most appropriate methods of midge control, such as stabling between dawn and dusk, use of ceiling fans to create a draught, fly repellents and anti-fly rugs. Immunotherapy may also be recommended (see below).

If allergen avoidance is not effective your vet may recommend a desensitisation programme called allergen-specific immunotherapy (ASIT). This involves injecting modified preperations of the appropriate allergens (identified with the allervet® test) in an attempt to create tolerance, and abolish clinical signs. Boosters are given every 4 weeks to maintain this state of tolerance. ASIT is available for most of the environmental allergens included in the test and to treat sweet itch.

What are the benefits of immunotherapy?

Your horse may need corticosteroid therapy (steroids) to control signs of allergy, but steroids can have serious side effects such as laminitis. Immunotherapy can help avoid the use of steroids, or at least significantly reduce the dose required. Successful immunotherapy can enable your horse to live a more fulfilled life without the risk of undesirable side effects.

If antibodies are detected against foods, supporting a diagnosis of food allergy or intolerance, the results can be used to select the most appropriate ingredients for a dietary trial. Everyone must be committed to helping your horse stay on this special diet.

Take the next step…

If you suspect your horse is suffering from an allergy, talk to your vet as soon as possible to discuss investigation, testing and treatment options.

allervet® testing is an important step on the way to helping your horse get better.

The allervet® service is offered exclusively in the UK by NationWide Laboratories, leaders in veterinary clinical pathology for over 30 years.

Allergic Disease

Many people suffer from allergies such as hayfever, asthma, eczema, rhinitis and conjunctivitis and are all too familiar with the misery they can cause. Similar symptoms are being recognised with increasing frequency in domestic animals including horses.

What causes allergy?

Allergy develops when the body’s immune system over-reacts to common substances in the environment called allergens. Examples include pollens – from grasses, trees and weeds, dust mites, moulds, organic dust such as hay dust, insects and certain foods.

Allergens enter the body following skin contact, inhalation or ingestion.

When an allergic horse is exposed to allergens it manufactures specific antibodies known as IgE’s. These antibodies bind to mast cells in the skin, respiratory tract or intestinal tract. After repeated exposure to allergens the mast cells release a variety of unpleasant chemicals which are responsible for the signs of allergy.

What are the common signs of equine allergy?

These can generally be divided into dermatological (skin) and respiratory signs:

Dermatological signs

  • Rubbing/itching poll, mane
  • and tail
  • Urticaria (nettle rash/hives)
  • Scabs, sores
  • Thinning hair/bald patches
  • Thickened, scaly skin
  • Swollen and/or watery eyes

Respiratory signs

  • Chronic coughing
  • Laboured breathing
  • “Heaves line”
  • Exercise intolerance
  • Poor performance
  • Nasal discharge

Headshaking and other head vices may also be caused by allergy in some horses.

What are the common allergies?

Sweet itch

This is a worldwide problem which results from an allergic reaction to the saliva of midges, or other biting flies, which is passed into the horse when the flies are feeding. The condition is seasonal and is generally seen from May through to October although there may be some regional variation.

Fly bites are intensely itchy for allergic horses. Self trauma (rubbing, nibbling, biting) results in hair loss from the mane and tail; crusty sores and thickened skin may develop along the middle of the back. Horses often become restless and irritable and may lose condition.

The age at which sweet itch develops is variable and depends on when the horse is first exposed (bitten). Not all horses are affected although a familial susceptibility is recognised.

Bites from flies such as stable flies, horse flies, black flies and mosquitoes may produce similar clinical signs.

Urticaria (hives)

This condition presents as well demarcated circular elevations of the skin which may appear anywhere on the body. Hives are often very itchy and may persist from several hours to days. Self trauma can result in secondary infection. There may also be oedema (swelling) of the head and around the eyes.

Hives may be caused by an allergic reaction to food, pollens, moulds, dusts, insect bites, medication or materials/substances in contact with the skin.

Recurrent airway obstruction/chronic obstructive pulmonary disease (heaves)

This debilitating respiratory disease, which is the equine equivalent of asthma, is thought to be associated with development of IgE to a range of environmental allergens, in particular hay and grain mill dust, moulds and pollens.

Exposure to these particles results in airway inflammation, increased mucus production and bronchospasm (narrowing of the airways). There may be irreversible lung damage if the condition is not diagnosed and managed correctly.

Equine atopy

This is an inherited condition; affected horses are genetically programmed to develop IgE against environmental allergens; exposure to these allergens may lead to the development of skin or respiratory tract disease. Clinical signs are similar to those seen with other allergic diseases.

How is allergy diagnosed?

Making a diagnosis and includes a horse’s history,

out all other causes of clinical signs such as parasitic lice

or mites, infection, adverse food reaction or drug reaction. Allergic disease is very much a diagnosis of elimination.

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