Of Horse

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Allergic Reactions
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Allergic Reactions

Mystery illnesses are every horse owner’s worst nightmare and sometimes diagnosis can be drawn-out and costly. Often, the symptoms are attributed to some kind of allergic reaction and a little detective work on the part of the owner and their vet can quickly reveal the cause of the problem.

Allergic reactions occur when the horse is exposed to something which causes his immune response to overreact to something (the allergen).

Common signs of an allergic reaction

· skin irritation; itchiness, reddening, welts or blisters

· swelling around the eyes; reddening of the conjunctiva and tears or thick, yellow discharge

· runny nose; coughing, noisy breathing

· diarrhoea; colic

· behavioural changes under saddle and in the stable

· sudden death


There are in the region of six different hypersensitivity categories. Sometimes a horse’s immune system may be sensitive to several different allergens which reside under the same category. In this case the symptoms he exhibits will be the same which makes isolating the cause of his condition very difficult. For example, your horse could be allergic to thistle pollen as well as barley straw; if he comes into contact with either he will show the same symptoms.

Identifying the allergen can be difficult as it can sometimes take a long period of time for the horse to build up sensitivity to a particular allergen. Other horses may exhibit a sudden, severe reaction to an obvious cause; for example a penicillin jab. It’s usually down to the owner and vet to consider the horse’s previous history and environment to see if there are any common denominators or if anything new has recently been introduced to which the horse could be reacting.

Common allergens include; injectable medications, dust, hay, grass, insects, grooming accessories e.g. show-shine, bedding, straight feeds like oats, barley etc.

Treatment and prevention

Obviously the treatment your vet prescribes will depend upon the nature of your horse’s allergic reaction. With skin conditions, an antihistamine will often be prescribed to be used in conjunction with some sort of topical treatment; cold water hosing or anti-inflammatory cream.

Preventative measures and husbandry will depend on the source of the allergen or suspected hypersensitivity.

· Insects: keep horses stabled during dawn and dusk hours when biting midges are most active; use a good insect repellent together with mesh rugs and fly masks and protect stable windows and half-doors with mesh to allow ventilation but keep nuisance insects out.

· Dust: where possible allow affected horses to live out; when stabled use dust extracted shavings or paper bedding rather than straw, feed haylage rather than hay.

· Grass pollen: try moving the horse to different grazing until the source of allergen is confirmed; keep the horse stabled until the pollen causing the reaction is no longer being produced.

· Grooming products: always do a patch test before using any sort of ointment, show gloss or shampoo on horses with sensitive skin; follow the manufacturer’s directions carefully when using the product and discontinue use if you are in any doubt as to its suitability for your horse.

· Drugs: NEVER give any drug to your horse unless it has been prescribed for you by your vet; always observe your horse carefully for adverse reactions following the administration of any injectable, especially penicillin.

If you buy a horse, always ask his previous owner if he has any allergies and if they are unsure, ask for their vet’s details and ask them.

Anaphylactic shock

Anaphylactic shock is fortunately quite rare in horses. It’s caused when the horse’s immune system malfunctions in its response to an allergen. Symptoms include; colic symptoms, breathing difficulties, hives, irregular heart rhythm and severe accumulation of fluid. Anaphylaxis is extremely serious. If the horse’s blood pressure drops too far or his breathing is severely compromised, he could die without immediate veterinary intervention.

If you suspect that your horse is suffering an allergic reaction, always consult your vet especially if you think he might have anaphylactic shock.


Disclaimer: Of Horse! and sponsors do not endorse nor validate the accuracy of a blog post. Each article is the opinion of the blogger.

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  1. arabobsession
    My mare was getting bitten by something at the begining of every summer, around her vulva. This resulted in a lot of swelling, and I couldn't find out what it was. She also developed a cough when being ridden. This year I changed where I get her hay from, the cough hasn't returned, and fingers crossed, she hasn't been bitten. How easy is it to not be able to recognize allergies, when the signs are so non descript. Loved the article, voted.
    1. autumnap
      Thank you!

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