An allergic reaction is defined medically as; “an inappropriate reaction of an individual animal’s immune system to a harmless agent that it is exposed to which the majority of animals will not react to.” Allergic reactions are broadly categorised into; insect bite reactions, food allergies, contact allergies and allergies to environmental agents like pollen, dust mites or fungal spores.
Insect bite reactions
In the case of insect bites, an insect will bite an animal in order to suck its blood and in doing so it will leave a small quantity of saliva which is then absorbed by the body. Some animals have an immune response which causes an excessive reaction to the insect saliva. The skin may become itchy and the horse rubs itself causing large sore patches, often with hair loss. A common example of insect bite allergic reaction is seen in Sweet Itch where affected horses and ponies rub their mane and tail area raw in an effort to relieve the itch. The midges or Black Flies which cause this reaction are most active and prevalent near standing water and when there are low winds in the early morning and late evening during the summer and autumn months. Prevention and effective management can bring some relief; stabling between 4pm and 8pm, fly repellent, a fine mesh screen across stable windows and doors and topical preparations of anti-inflammatory medication are all good ways to combat this nuisance.
Another allergic reaction to an insect bite is Hives or Uritcaria. This is caused by a sting from a wasp or a bee and causes large swellings all over the body. Although distressing for the horse at the time, the condition is quickly resolved through the administration of appropriate intravenous medication by a vet.
Some horses are allergic to certain types of medication. Certain types of wormers can trigger an alarming reaction in which the skin becomes covered in large, irregular bumps. Such a reaction generally resolves itself over a short period of time and obviously it’s best to avoid using a similar type of wormer in the future. Your vet will be able to advise you on a suitable alternative.
Environmental agents can affect the horse either through direct contact with the skin or through inhalation. A favourite cause of such a reaction is a change in bedding material for example a change from wheat to barley straw. The skin may become covered in small, hard lumps which may affect all of the horse or just the areas which have been in contact with the allergen. A short course of antihistamine usually settles things down within a few days. Some horses cannot tolerate certain kinds of fabric so rugs can cause itchiness and spray on show gloss, shampoos etc can also cause problems.
Certain breeds appear to be more prone to inhalant allergens (atopic dermatitis) than others; Arabs and Thoroughbreds in particular. The usual suspects are pollens, moulds and dust mites. The skin becomes inflamed and itchy and the horse scratches and rubs itself causing sores, hair loss and ulcerated lesions. If no obvious cause presents itself, your vet will be able to carry out allergy testing to identify the source of the problem. This can be problematic and lengthy as many allergies only manifest themselves at certain times of the year or during particular climactic conditions.
The best cure for skin allergies is prevention. You know your horse better than anyone else does so keep a close eye on him, checking him over daily as you go through your grooming routine. If you notice anything unusual; lumps and bumps, slightly raised areas of his skin which feel hot to the touch, rubs and sore patches where the hair has been lost etc be on the alert. What’s different in his environment? If anything has changed which coincides with the skin condition he is presenting, change it back! Of course, if you are concerned always speak to your vet.
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