Allergies in Horses

Symptoms including itchiness, over-excitable or irritable behaviour and loose droppings are often described as allergies by horse owners and may be attributed to various different ingredients including molasses and alfalfa. But can horses have allergies? Are they truly allergic reactions and if so, how do we best manage them?

What is a food allergy?

A food allergy is defined as “an immune-mediated adverse reaction to food”. In practice this means that the body has a reaction to a food which would not normally cause a problem for most individuals. Food allergies are triggered by allergens such as specific proteins found in some foods. Allergy symptoms range from a mild condition such as urticaria (lumps and bumps on the skin that may or may not be itchy) to very serious conditions such as anaphylactic shock. In humans for example, this may be caused by a peanut allergy. Horses can be allergic to anything that contains a protein. They may be fed certain feeds or ingredients for many years but then develop an allergy to it even if nothing about the feed has changed. Allergies can be triggered by a challenge to the immune system such as vaccinations and de-worming or even a stressful event occurring.

What is a food intolerance?

In contrast to an allergy, a food intolerance is a non-immune mediated adverse reaction to food. This type of reaction does not involve the immune system and tends to illicit milder symptoms than a food allergy. An example would be lactose intolerance in humans.

How common are food allergies and intolerances in horses and ponies?

True feed allergies are thankfully quite rare in the horse, however allergic reaction type responses can occur for a variety of reasons. For example, the typical ‘protein bumps’ may be triggered by allergic reaction to anything from a fly bite through to contact allergies to bedding or rugs, rather than being anything to do with the amount of protein the horse consumes. There are also a wide range of skin conditions which may trigger similar symptoms, so it is always best to seek veterinary advice. It is important to note that horses with a food allergy are likely to exhibit symptoms such as urticaria all over their body and not just within one location.

When it comes to food intolerances, the definition of this in horses is much more ambiguous and may not mean that the horse is actually allergic to something. The reason for this is that many people would describe a change in their horse’s behaviour, such as becoming more excitable, as an intolerance to a type of food when in fact there are many other issues that could be involved. For example, excitability in horses may be related to the amount of energy consumed in relation to workload, variability in exercise level and even environmental factors such as how windy it is. If these changes happen to coincide with a change in diet, it is easy to see why the feed often gets the blame.

How do I know what my horse is allergic to?

If you are concerned that your horse or pony may have an allergy or intolerance to something in their feed, it is recommended to start with an elimination diet to determine if this is truly the cause. This involves removing all bucket feed for a minimum of four weeks but potentially up to eight weeks depending on the severity of the symptoms your horse is experiencing. If your horse’s symptoms continue in this period and do not get any better, then it is likely that the feed is not the culprit. In this instance, the next step would be to consider if it is something in the environment causing the problem or if the forage can be gradually changed to see if this helps.

However, if the symptoms do improve, it is possible that the feed is the issue. To confirm this, once the symptoms have completely resolved, feeds should then slowly be reintroduced one by one (including any that are suspected to be causing a problem) to see if the symptoms reoccur. Feeds should be introduced gradually, leaving at least a week between each new reintroduction. If the symptoms do then reoccur, you can then be fairly confident that something within the feed could be causing the problem.

It’s really important to try reintroducing the horse’s original feeds for this second part of the trial, as many symptoms that could have been caused by something else in the environment or another illness may naturally resolve by themselves in this time and it could have had nothing to do with the food. If there is no reaction to the feed being reintroduced, then it was probably not a feed allergy.

Once you have determined that it is likely to be something within the feed that’s causing the problem, the next step is to start with a clean slate or an empty feed bucket and reintroduce different ingredients. Single ingredients feeds such as Dengie Pure Grass Pellets, Alfalfa Pellets or unmolassed sugar beet pulp are a great way to get started – reintroduce one feed at a time, again leaving at least a week in between, to be sure you know which ingredients have no effect.

Elimination diets do involve a lot of trial and error and can take time and patience, but they are worth persevering with to help you best manage your horse’s health in the long term. Remember that many feeds share similar ingredients so simply switching from one brand of feed to another would not constitute a proper elimination diet or feed trial. For further help and advice on elimination diets it is worth speaking to a nutritionist.

If a specific allergy is identified, it can be difficult to find a mix or cubes that excludes the ingredient concerned, so look for feeds which list the full ingredients on the bag – if in doubt contact the manufacturer. An alternative option is to use straight feeds, like those listed above, alongside micronised linseed if more calories are required, and this can make a great combination for horses with allergies or intolerances to feeds such as barley or molasses.

In addition, it is important to add a source of vitamins and minerals which can be fed in the form of a powder supplement or a balancer. Balancers will contain a range of ingredients and so supplements are often easier to use as they are just vitamins and minerals with a base carrier ingredient usually included at low levels.

If you feel that the horse’s diet simply does not seem to suit them but that it may not be a specific allergy (for example some horses seem to show ‘fizzy’ behaviour when fed cereal-based feeds), then consider feeding a natural fibre-based diet. Feed plenty of good quality forage and feeds high in digestible fibre, which will provide predominantly ‘slow-release’ energy. Examples would include sugar beet pulp and Dengie Alfa-A feeds. Alfalfa will provide a similar feed value to many cool mixes or cubes but is high in digestible fibre and so, when fed in conjunction with a broad-spectrum supplement, is an ideal cereal-free alternative to normal compound feeds.

Are allergy tests helpful?

Whilst allergy tests for horses can seem like a much more straightforward way of identifying allergens compared to an elimination diet, they do vary in their reliability. A study by Dupont and colleagues in 2016 examined the efficacy of a commercially available blood test in ponies. They conducted the test on two separate occasions in the same group of ponies and got different results each time – only one pony had a positive result twice for the same allergen! Following this, they then fed the ponies with the ingredients that had been highlighted in the blood tests and there were no adverse reactions at all. This suggests that allergy test results should be interpreted with caution and should not be relied upon to accurately diagnose an allergy. Although they can sometimes provide a useful starting point, it is often much more helpful to observe your horse’s reaction to different feeds and use elimination diets to determine which feeds they can cope with. This is especially relevant when we have to balance the results of an allergy test with other requirements such as fussiness or other health problems when it may become much more challenging and costly to source an appropriate feed.

Alfalfa Allergies in Horses – Do they exist?

In theory, horses can be allergic to a range of different ingredients including alfalfa. Horses may be allergic to a particular protein in an ingredient which could trigger an immune reaction, meaning that the ingredient should be avoided. Symptoms such as grumpiness or loose droppings are more likely to be due to an intolerance which is often correlated to the amount of an ingredient that is fed. For example, some people say they can’t feed Alfa-A to their horse because it contains alfalfa but are using Hi-Fi (which contains around 45% alfalfa) without any problems. As avoiding some commonly used ingredients altogether can be tricky, it is advisable to differentiate between an allergic reaction and an intolerance in the first instance and then determine whether the horse can cope with smaller amounts in their ration. However if your horse really cannot cope with even a small amount, then alfalfa-free feeds in the Dengie range include Pure Grass Pellets, Meadow Grass with Herbs & Oil and Meadow Lite with Herbs.

Grass Allergies in Horses

If your horse is allergic or intolerant to grass but not alfalfa then feeds such as Dengie Hi-Fi Lite, which combine alfalfa and straw, can be used as forage replacers. Dengie Alfa-Beet, which combines alfalfa and sugar beet pulp, is also ideal for providing more fibre without using grass. It is possible to use some straw as part of your horse’s forage ration, as long as it is introduced gradually. This can work particularly well for good doers or those who are overweight as straw typically provides fewer calories than grass-based forages. Research suggests that up to 50% of the horse’s forage requirement can be fed as straw each day (Jansson et al., 2021). Straw wouldn’t be ideal for those with dental issues though or those prone to impaction colic, and so it is worth speaking to a nutritionist for more specific advice here if you are unsure. More information on feeding straw can be found here.

Supporting your horse from the inside

A large part of any animal’s immunity is within the gut. Horses have evolved to eat a fibre-based ration and would naturally spend around 16-18 hours per day eating. The stresses of domesticated life, including competition and travel, can disrupt the population of micro-organisms within the horse’s digestive tract. This can lead to loose droppings and poor coat condition.

Digestive enhancing supplements typically combine ingredients like prebiotics with live yeast which helps to create favourable conditions in the horse’s gut for beneficial fibre digesting bacteria to thrive. They can be fed at a concentrated level at times of stress or may be fed daily at a maintenance level.

Ensuring your horse receives a balanced ration with respect to vitamins and minerals is another way to support your horse from the inside, especially as certain vitamins and minerals have an important role as antioxidants and therefore are vital for immune function. If you are feeding a fibre-only ration, or less than recommended amounts of a fortified feed, then it is advisable to add a vitamin and mineral supplement or balancer.

Fact or fiction?

When it comes to food allergies and intolerances, there are a lot of common feeding myths to be dispelled.

My horse is allergic to protein – fiction!

This is a very common misunderstanding often due to the fact that some allergic conditions in horses such as urticaria are also called protein bumps. An allergy is not caused by the amount of protein found within the diet, but instead by a specific allergen, which is a specific type of protein, found in some foods. For example, if a person was allergic to the protein in peanuts, they could still eat meat which also contains protein.

My horse is allergic to sugar – fiction!

Molasses is often said to be the cause of allergies and because molasses have a high sugar content, horse owners assume that all sugar is going to have the same effect. This is not the case as sugar is present in all commonly used plant materials for horses such as grass, hay, cereals, alfalfa and sugar beet pulp, albeit at low levels. If a horse was allergic to sugar, there would literally be nothing they could eat.

My horse is allergic to cereal grains – possibly

It is possible for some individuals to be allergic to cereal grains as some are known allergenic foods and this may result in symptoms such as urticaria and itchy skin. Rice is often referred to as hypoallergenic and so may be a suitable alternative to other cereals.

Sweet Itch in horses

The correct term for Sweet Itch in horses is insect bite hypersensitivity (IBH) which is an allergic reaction to the saliva of biting insects, particularly the Culicoides midge. The hypersensitivity reaction in affected individuals results in histamine being produced by the body’s immune system, leading to inflammation, swelling and intense itching. Other symptoms that usually accompany the skin reactions include changes in temperament and irritability, head shaking, tail swishing and excessive rolling or scratching. Sweet itch can affect all breeds of horse, but certain types such as cobs and natives seem to be more predisposed to developing the allergic reaction. There may also be a genetic link.

Symptoms of Sweet Itch usually appear between March and October which is the time of year when flies and insects are most active. Horses are commonly affected in the areas around the mane and the top of the tail, since these are the areas that midges usually prefer to feed, but reactions can also occur anywhere on the body where midges might land and bite.

Unfortunately, no cure exists for Sweet Itch, and it often can become worse each year once the allergy has developed. Management strategies involve minimising the horse’s exposure to the midges, for example by avoiding turnout areas near woodlands or water where flies and midges are more abundant, as well as stabling at dawn and dusk. Using fans in the stable may also help to keep the midges at bay. Fly rugs or specific sweet itch rugs are also thought to be very effective, along with fly repellent sprays. Topical lotions may help to relieve discomfort in the affected areas, and your vet may suggest short term medical treatment to help reduce the severity of the symptoms.

Will changing my horse’s feed help with their Sweet Itch?

Since the symptoms of Sweet Itch are caused by an allergic reaction to insect bites and are not related to feed, there is no evidence to suggest that removing or avoiding certain ingredients in your horse’s diet will improve their condition, assuming there are no other underlying allergies. However, ensuring you are providing a balanced diet for vitamins and minerals is a good place to start as this will help to support overall immune function. Omega-3 fatty acids may also be helpful as they have anti-inflammatory properties and so may reduce itching. The best source of omega-3 is fish oil because this contains EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), which are in the form that the horse needs them. For those who prefer not to feed fish oil, hemp oil is another option; however, this should be avoided for horses who compete as it contains cannabinoids which is a prohibited substance (NOPS). A relatively new ingredient becoming more widely available is ahiflower oil. This is a great source of essential fatty acids particularly omega 3 and is a more sustainable option than fish oil and is okay from a NOPS perspective too.

More resources and information on sweet itch can be found below:

• World Horse Welfare
• Liphook Equine Hospital

Key Takeaways:

• True feed allergies in horses are rare.
• Allergy tests can be unreliable, and an elimination diet is widely considered to be the most appropriate way of identifying a feed allergy.
• Single ingredient feeds like grass pellets, alfalfa pellets and unmolassed sugar beet pulp can be useful options for horses with allergies or intolerances.
• These feeds should be fed alongside a balancer or vitamin and mineral supplement to provide a balanced diet which is important for supporting the immune system.
• Promoting good digestive health by feeding plenty of fibre and incorporating digestive aids can also be beneficial.
• Sweet itch is caused by an increased reaction to fly bites rather than being directly associated with specific feeds or ingredients.

References

• Dupont et al., (2016). A commercially available immunoglobulin E‐based test for food allergy gives inconsistent results in healthy ponies. Equine Veterinary Journal, 48(1), pp.109-113.
• Jansson et al., (2021) Straw as an Alternative to Grass Forage in Horses—Effects on Post-Prandial Metabolic Profile, Energy Intake, Behaviour and Gastric Ulceration. Animals. 11.