By vet Bethan Harper
The summer season brings warmer weather, longer days, and hopefully, less mud in the fields!
Unfortunately, it can also bring a host of new allergens to cause difficulty for your horses, including insects, pollen, and fungi. Seasonal allergies most often cause problems for both the skin and the respiratory tract.
A well-known skin issue affecting horses in summer is sweet itch – also called ‘Insect Bite Hypersensitivity’ or IBH. This occurs when horses have a hyperimmune response to the saliva of biting insects, most often the Culicoides midge. The saliva in the bite causes pruritic (itchiness) leading to the horse scratching and traumatising the skin further, which leads to more pruritis. This vicious cycle can lead to the skin becoming extremely damaged and can have serious welfare implications for your horse. Affected horses will often have visible damage to their manes and tail where they have rubbed as well as skin irritation or open sores.
There is no cure for sweet itch, and management mostly focuses on reducing exposure to biting insects by using fly repellents, masks and rugs, as well as avoiding turnout at times of high midge activity (usually around dawn and dusk). There is also a vaccine available that can be used to help reduce the clinical signs associated with sweet itch. This is an off-licence product developed to treat ringworm in cattle, but it has been shown to be effective for use in sweet itch cases. It is important to note that this is not an alternative to management changes, but an adjunct to be used alongside them. This vaccine works best if given before the onset of clinical signs, so aim to get it done around February in preparation for the summer season.
Atopic dermatitis is an allergic skin condition defined as an abnormal immune response to environmental triggers and is most often seasonal. It is linked to IBH, and the conditions are often seen together. The symptoms are similar, with horses becoming pruritic which leads to redness, flaky skin, and alopecia. In some cases, severe self-trauma can lead to secondary infections. Affected horses may also present with hives. As with IBH, the mainstay of management is to reduce exposure to triggers, which may require time invested into determining what the main triggers are. Your vet may prescribe a short-term treatment with corticosteroids to help break the itch cycle, or topical treatments to use on affected patches of skin. Horses will often benefit from dietary support to improve skin and coat health as well.
Summer allergies can also be a trigger for equine asthma. Many people associate equine asthma with dust found in stables and dry hay, but there is a subset sometimes referred to as summer pasture associated asthma, or SPA asthma. These cases are triggered by pollens or fungal spores, and symptoms appear with increased turnout time during warmer months. Symptoms include coughing, difficulty breathing, exercise intolerance, and sometimes nasal discharge. As with any case of equine asthma, reducing exposure to allergens is the best way to reduce symptoms. This may mean your horse has to be stabled when the pollen count is higher, or they may benefit from wearing a fly mask with a fine mesh over the nose to filter pollen. A nose net can also be used when riding. Medical treatment for equine asthma involves reducing inflammation, clearing mucus and opening up the airways. Your vet may use injectable or oral drugs in the first instance, but for horses requiring long term treatment the best option is to transition onto inhaled medication using a nebuliser.