Allergic reactions (also known as hypersensitivity) can affect any horse at any time, and can even be in response to a stimulus which the horse has previously been in contact with. Allergic reactions occur when the horse’s immune response overreacts to an allergen.

Symptoms

A horse producing an allergic reaction can show any number of the following symptoms:

• Irritated skin (reddening/or itchy)
• Welted skin (aka hives)
• Blistering skin
• Runny eyes, swelling around eyes or ‘conjunctiva’
• Runny nose
• Coughing or sneezing
• Labored breathing
• Asthma, bronchospasm or larynospasm (difficulty getting air)
• Swelling in nose
• Diarrhoea
• Colic
• Unusually intolerant to handling or exercise
• Unusual demeanor
• Sudden death from anaphylactic shock

There are at least 5 to 6 different categories of hypersensitivities. If a horse’s immune system is hypersensitive to 2 or more different allergens, but they are under the same category of hypersensitivity, then the symptoms displayed will be the same. For example, a mare could be allergic to oats as well as couch grass. If they are in the same category of reaction. You’ll find when she comes into contact with either she shows the same symptoms of welts and/or labored breathing.

Diagnosis

A horse’s immune response can take a very long time to build up sensitivity to an allergen, thus it can often be very difficult if the owner and vet are unable to pinpoint the stimulus. In other cases a single exposure can cause the hypersensitivity and the next exposure results in a severe reaction. As an example, a penicillin reaction leading to death on the 2^nd dose of penicillinDue to the vast range of symptoms, it can often take some time to accurately diagnose many allergic reactions, and then develop a treatment/or prevention plan. You and your vet would examine the horse’s past to determine if there was anything new introduced recently. If nothing has new has been introduced a close examination would be required of the period leading up to when the horse appeared to be reacting.

Stimuli

As you can probably guess, there are nearly as many allergens as there are types of cells! The most common ones we see in our practice include:

Different types of grass, oral injectable medications, dust, hay, insects, cleaners, topical ointments, etc. There are many many more but these are things which horses commonly come into contact with.

Treatment of a Reaction

If your vet has diagnosed your horse’s symptoms as being an allergic reaction, they make provide a specific antiinflammatory medication as well as pain relief for the period of recovery. Symptomatic support may be required depending on the horse’s presentation. Welts can often be eased with icing /or cold water therapy. An allergic horse with colic or diarrhoea may need intensive care. The best treatment of course is to identify and remove the trigger, in milder cases the associated symptoms will subside accordingly.

Prevention of Allergic Reactions

Prevention lies with identification of triggers and their removal. Your vet will be a good guide as to an appropriate course of action.

Here’s a few common allergies and tips to reduce their effects:

• Dust – keep horse in a well-grassed paddock, wet down feed, do not use sawdust and other similar materials for stabling, something like Animal Ecobedding could be a viable alternative

• Insects such as midges – keep horse rugged where possible (mesh rugs are good for the hot Queensland summer), insect repellant applied at least twice a day, or as per instructions (we use Flyaway)

• Grass – move the horse to a different paddock, move the horse to a different property, rug, keep grass low, keep stabled or in dirt/sand paddock (at increased risk of sand colic).

• Topical ointments – do a patch test first, where you apply the ointment to a small area and assess response. Only use the ointment as the label directs.

• Cleaning products – avoid harsh chemicals where possible, ensure all residue is thoroughly washed off before it comes into contact with your horse

• Drug reactions – another reason to never give any drug (including bute) without a prescription from your vet. Reactions, particularly to sedatives, are quite common hence horses should only be sedated under veterinary supervision. Other injections, eg penicillin, may also cause allergic responses and strict observation of administration instructions is helpful, but unfortunately not always preventative.

When purchasing a new horse don’t forget to enquire about whether it’s had any allergies or appears to be sensitive to anything. Many allergies are manageable and will probably not sway your decision to purchase a horse, but could prevent a big vet bill if a nasty reaction occurs.

Always call your vet if any of the aforementioned symptoms appear, as fast action can reduce the risk of your horse going into anaphylactic shock and possibly dying.