Recognising and managing allergies in horses can be challenging for owners, vets and at times nutritionists. While an acute allergic episode can present a real veterinary emergency, chronic allergies can prove to be a long-term welfare concern for the horse. Depending on its nature, allergic reactions can resolve themselves fairly quickly after a short course of medication. However, chronic allergies with for example a persistent rash, commonly referred to as hives, and intense itchiness can result in skin trauma, due to scratching and rubbing. Diagnosing the trigger or cause of the allergy can be the most challenging part.
Allergies or hypersensitivities can be categorised in to five subdivisions:
- Insect bites
- Medication reaction
The most common insect bite hypersensitivity is known as sweet itch and is due to an allergic reaction to the saliva of the Culicoides midge. Medication reactions can occur to almost any type of medication, systemic or topical, but these are usually quickly recognised and easy to pinpoint and manage. The vet should always be contacted if you suspect a reaction to a medication and a record of the medication should be kept. Contact allergies are environment related and may include an allergy to certain types of bedding, topical application, shampoos etc. Respiratory allergies, for example to pollen, can result in persistent coughing, nasal discharge and reduced exercise tolerance.
Feed allergies, although rare, occur in response to a specific type of protein and can be complicated to diagnose and manage. True food allergies differ from food intolerances, as they always involve the immune system and will be the focus of this article. Veterinary advice should always be sought if you suspect an allergy of any kind.
Insect bite, feed and contact allergy/hypersensitivity can all result in atopic dermatitis, which refers to a long-term sensitivity to environmental allergens or feed resulting in intense itching (pruritus). Causes or triggers can include dust, storage mites, insects, pollens and feed ingredients.
Evaluation of feed allergies in horses is very difficult due to the wide variety of potential ingredients that may be the cause of the problem. Results are often inconclusive and false positives are common, indeed the horse can also show an apparent hypersensitivity to an ingredient it’s never actually reacted to. This means that expert evaluation of the horse and the results of allergy testing are key to diagnosing and managing the problem.
The most common way to diagnose allergies in horses is to carry out an Intradermal Allergy Test (IDAT). This is essentially a panel of intradermal injections, each of which contains a single known allergen. A qualified veterinarian, often one which specialises in dermatological issues, will carry out the tests and they will have a way of determining the panel of allergens to be tested. Most commonly the panel will include moulds, pollen and specific proteins from things such as insect saliva and certain feed ingredients and mites. The injections will most commonly take place on the horse’s neck covering an area the size of an A4 piece of paper, each one a couple of inches apart. The veterinarian will be looking for a skin reaction local to the area of the individual injection/allergen. The extent of the skin reaction will be measured for a number of hours after the injections are made and further interpretation of the results will take place.
A common question is can allergies be assessed by taking a blood sample? Although this would be much more convenient, it is not as reliable a method as the IDAT due to the way in which the body secretes the main antibody or immunoglobulin associated with allergic reactions. Blood samples are still regularly taken and can be very useful in the investigation of allergic reactions. Immunoglobulin E (IgE) is most abundant in the skin (compared to serum) where it is attached to what are known as mast cells, this immunological combination is a key element in the development of actual red lumps and the skin reaction that we associate with allergies. The IgE recognises/encounters the allergen and in turn the mast cell bursts causing the skin reaction, the IDAT is based on this principle and is the reason why it is considered a more reliable method of diagnosing allergies in comparison to a serum sample. Your vet will always advise what they believe to be the most appropriate method(s) to investigate your horse’s allergy.
Feed allergies are often the most concerning and disruptive to owner and horse in terms of the limited methods of management. For example, many feeds contain similar ingredients often varying only in amount, and if your horse is found to be allergic to one specific grain such as barley then your choice of feeds will be limited. It is therefore very important that results are interpreted as accurately as possible to avoid any unnecessary insults to your horse’s diet and most importantly ensuring the horse still receives an all-round well-balanced diet, providing all the necessary nutrients required. It is especially complicated when feed allergies present themselves in the performance and breeding horse as their energy and nutrient demand is more complex and extensive than others.
Clinical signs of feed allergies are similar to other types of allergies and usually consist of hives, itchiness and possibly self-trauma due to the scratching. Diagnosis is often confounded by the high likelihood of the IDAT showing hypersensitivity to something the horse commonly eats and may not have reacted to before. The only definitive and dependable way to confirm a feed allergy is to completely remove the suspected food from the ration for at least 4-8 weeks to see if there is an improvement in clinical signs. If the IDAT cannot identify a potential feed allergen then a practical way to further investigate is to remove concentrates and all supplements from the ration and allow clinical signs to reduce and when they do slowly reintroduce specific ingredients and monitor closely for recurring signs. This is not a popular method for horse owners, but it may be necessary. When it is carried out all changes should be made slowly and an accurate food diary can be very useful.
Treatment of allergies should focus on finding the cause and eliminating it, i.e. allergen avoidance. However, there will be times when medication is required and in these circumstances your vet will most likely administer topical therapies and systemic medications such as antihistamines and glucocorticoids (steroids). Owners can offer nutritional support to their allergy affected horse with certain supplements that help to support skin health such as Foran Equine Kentucky Karron Oil and the multi vitamin and mineral liquid Foran Equine Chevinal. Foran Equine Kentucky Karron Oil provides an excellent level of Omega 3 fatty acids which have natural anti-inflammatory properties and are thought to be very useful when the horse is suffering from allergies. Foran Equine Chevinal provides an extensive number of essential vitamins and minerals, such as biotin, iodine, zinc and methionine all of which are thought to play a major role in maintaining skin health and quality. The addition of antioxidants such as Vitamin E can also be helpful when feeding an allergic or hypersensitive horse. Depending on what the feed allergy trigger is a feed balancer can be an excellent source of nutrients when the use of a cereal-based mix or cube is contraindicated.
Allergies in horses remain a challenging and complicated subject for veterinarians, nutritionists and horse owners and it is clear that a multi-modal approach to management is key, including allergy testing, allergen avoidance, topical and systemic medications and targeted nutritional and supplement support.