Solving summer skin problems in horses

Breaking the cycle of persistent irritation is the key to coping with summer skin problems, explains Karen Coumbe MRCVS

The skin is the body’s largest organ, serving as a protective wrapping against the elements. It quickly becomes obvious when something goes wrong with this outer layer – especially in these warmer months, when a combination of sunshine and insects can worsen skin irritations.

Itchiness, properly termed pruritus, is more than merely a cosmetic issue. The discomfort can irritate a horse to the point that he loses weight, and in severe cases it can even be confused with colic. A skin problem can become a serious welfare matter, since an itch is actually a modified form of pain.

We all know how irritating an itch can be. The unpleasant sensation leads a horse to bite, scratch or chafe his skin, which may be rubbed raw. In desperation, he may resort to finding a fence post or similar for relief.

For long-standing or recurrent itchiness, try to establish the reason rather than just disguising the signs with antihistamines, which rarely work well on their own, or steroids, which are effective but can have side effects.

It is far better to work with your vet to identify a cause, so that more specific and focused treatment can be selected where available. Giving your vet detailed information about your horse’s history and current lifestyle will often provide vital clues.

Attack zones

The most common causes of equine pruritus are parasites, such as lice and mites, which tend to be a worry in winter, and allergic reactions that are more commonly seen in summer.

Sweet itch is a classic summer skin problem; it is rarely encountered when temperatures drop below around 4°C and the biting midges stop flying. Reported to affect more than 5% of the UK’s equine population, and more often ponies and heavy breeds, the condition is an insect bite hypersensitivity caused by an allergy to irritants in midge saliva.

Typical signs include mild to severe itching and rubbing, usually along the mane, back and tail. Areas of sore, open or broken skin may bleed and the resulting bald patches can appear ugly and grey due to permanent hair loss and skin damage.

Different midge types attack different anatomical areas, resulting in varying distribution patterns of soreness. As fly rugs protect the standard midge attack zones, vets frequently see cases where the itching is worse elsewhere and is not always immediately recognised as sweet itch by the owner. A study recently showed that of 12 horses exhibiting clinical signs of sweet itch on veterinary examination, only one of the owners thought one horse suffered from the condition.

Sweet itch can usually be diagnosed on the basis of the typical summer itchiness together with a history of exposure to biting midges, which are at their worst around dawn and dusk, especially in warmer, damp weather. Although bigger flies also plague horses, they tend to cause more localised, painful reactions and skin lumps.

Catching rays

Sunburn can affect horses with pink skin, particularly around the muzzle and heels, or in damaged, depigmented areas.

Grazing with good shade available is clearly best, otherwise avoid turnout in the middle of the day. Apply a high-factor sunscreen to sensitive areas and consider using UV-protective turnout masks, rugs and boots.

A separate condition easily confused with sunburn is photosensitisation, where skin becomes overly sensitive to UV light and is irritated by sunlight. This usually occurs in areas without much hair or with white hair – the face and heels, again, but also the lower limbs.

The horse may become uncomfortable, scratching the affected areas until they become sore. If the condition is caught at this stage and he is taken out of direct sunlight, then the problem will usually resolve itself. However, if exposure to sunlight continues, discomfort will increase as scabs form in the sensitised areas. Medication may then be necessary.

Photosensitisation can also be a side effect of liver damage – sometimes linked to eating poisonous plants like ragwort – as a damaged liver is unable to break down toxins effectively. Your vet may want to run blood tests to rule out liver problems.

Lesions and lumps

Certain summer skin issues may be less itchy but nevertheless troublesome. Sunshine can trigger leukocytoclastic vasculitis, which typically affects the white-socked lower limbs of pasture-kept horses and is commonly found on the outside of the cannon bone.

If you notice that your horse has something similar to mud fever when the weather is dry or sunny, it is more likely to be leukocytoclastic vasculitis. A biopsy of the skin may be needed to make a definitive diagnosis, but a vet will usually diagnose this by observing the fairly typical lesions.

The area may be quite sore in the early stages, when the skin breaks out in crusting or ulcerative scabs, and may develop secondary bacterial infection. Treatment relies on avoiding light, ideally stabling your horse during the daytime or using some form of UV light-protective leggings. There are a variety of “sun socks” on the market, but they do need to stay in place without rubbing to be safe and practical for turnout.

Applying soothing creams can help, but corticosteroids, administered topically or as tablets or an injection, may be required in severe cases. The condition can result in disfiguring dermatitis if left, so is best treated immediately.

Squamous cell carcinoma is a cancer that affects the margin between the skin and the lining tissues around a horse’s eyes, nostrils and other areas such as the penis and vulva. This relatively common condition accounts for approximately 20% of all equine mucocutaneous (where skin meets mucous membrane) tumours and often presents vets with a therapeutic challenge.

Risk factors include chronic exposure to ultraviolet light and chronic skin irritation, particularly in horses with less pigment in these areas, such as palominos, cremellos and Appaloosas. Early recognition of tumours and prompt intervention is associated with a positive outcome, so consult your vet immediately if you notice a problem with your horse.

Sweet itch: the latest thinking

Hopes for a solution to this frustrating condition have been dashed many times, when tests on potential vaccines or other purported cures have proved inconclusive. Recently, vets have been using a European ringworm vaccine, but there is no UK licence for the product. Experts are optimistic, however, that a suitable vaccine may be produced.

In the meantime, prevention is better than treatment. It is crucial to take a multimodal approach to break the itch scratch-itch cycle:

• Apply a good insect repellent at regular intervals – your vet will be able to advise you. There is some evidence that certain products such as citronella may actually attract midges.
• Move grazing away from still water, such as ponds. An area with a strong breeze, such as a hilltop or coastal field, is ideal.
• Keep your horse’s skin covered while he is out grazing with a full, lightweight rug designed to prevent the condition. Midges will get through tiny gaps, so use barrier lotions as well – again, ask your vet.
• Clear the yard of any stagnant water, where midges typically breed, and clean water troughs regularly.
• Stable your horse from around 4pm–8am, to avoid the midges at their worst. Insect-proofing buildings with a fine mesh material will also help.
• Install a sturdy ceiling fan that blows air downwards, if safe to do so, since midges cannot fly against a strong air current.
• Bathe the horse with a soothing shampoo, especially in hot weather.
• Consider trialling feed supplements designed to support skin health; while there is limited scientific research regarding their efficacy, anecdotal evidence suggests that they may help.

Ref Horse & Hound; 2 July 2020

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