Allergies in horses: recognising and addressing symptoms

What exactly is an allergy in a horse?

An allergy is an exaggerated response of the immune system to a substance that is not harmful in itself, such as pollen, moulds, or certain feed components. The immune system perceives such a substance as a threat and responds with inflammatory reactions. Allergies in horses are more common than many people think: it is estimated that 10 to 15 percent of all horses experience an allergic condition at some point. Distinguishing it from an infection or other condition is not always possible without a vet, but the symptoms already point you in a first direction.

The most common symptoms at a glance

Allergy symptoms in horses manifest in three ways: through the skin, the airways, or the digestive system. If you recognise one or more of the symptoms below, further investigation is advisable.

• Intense itching, often around the mane, tail, belly, or legs
• Bald patches, scabs, or sores from scratching and rubbing
• Coughing, wheezing, or rapid breathing during or after exercise
• Watery or thick discharge from the nose and/or eyes
• Hives: round, raised bumps on the skin
• Diarrhoea or a bloated belly without a clear alternative cause

Common allergens in horses

The trigger varies from horse to horse, but a few sources come up time and again. Hay allergies (caused by moulds and dust in hay) are the most common cause of respiratory problems. Insect saliva from midges (Culicoides) causes the well-known sweet itch reaction in approximately 3 to 5 percent of horses in the Netherlands. Feed allergies are less common but do occur with grains, soya, and certain herbs.

• Moulds and dust in hay or straw
• Saliva from midges (Culicoides species)
• Pollen from grasses and trees (seasonal)
• Feed components such as grains, soya, or field beans
• Chemical substances in grooming products or rubber equipment

Sweet itch: specific recognition

Sweet itch is one of the best-known allergic skin conditions in horses and is caused by midge bites. It typically begins in April or May and does not disappear until the midges are gone, around October. You will mainly notice itching and hair loss on the mane, tail base, and belly line. Some horses damage themselves so severely through rubbing that open wounds develop. A horse with sweet itch has a genetic predisposition; it occurs more frequently in Icelandics, Friesians, and Welsh ponies. Record the first symptoms of each season in your horse's EquiSight horse profile so that you can spot a pattern and take action in time.

When to call the vet straight away?

Some situations call for prompt action. Call your vet the same day if you observe any of the following.

• Severe respiratory distress or wheezing while at rest
• Sudden hives across the entire body after contact with a new product or feed
• Open, bleeding wounds from self-mutilation due to itching
• Persistent diarrhoea lasting more than 24 hours combined with other symptoms
• Significant swelling of the head, lips, or legs without a clear cause

Practical steps to reduce allergy symptoms

You can rarely eliminate an allergy entirely, but you can substantially reduce exposure to the allergen. Wet or soaked hay produces up to 90 percent less dust than dry hay. For sweet itch, a well-fitting fly rug that also covers the belly helps, as does stabling from one hour before sunset until one hour after sunrise, when midges are most active. Use the calendar in EquiSight to track treatments and reactions, so that you and your vet can quickly see what is and is not working. You can also ask EquiCoach for a personalised checklist based on your horse's profile data.