Sun Damage: How the Sun can Damage Horses

Sun Damage: How the Sun can Damage Horses

Horse Health – Sun damage – Everything Horse Magazine

Whilst we all love the weather that British summer time can provide, sun exposure can be as problematic for horses as it is for ourselves. Here Anna Hollis, Senior Clinician in Equine Oncology at the Animal Health Trust, takes a look at the hidden dangers of sun burn and squamous cell carcinoma

Sun burn and the hidden dangers

Horses with poorly pigmented areas of skin are at high risk of sun damage developing into sun burn. Commonly affected areas are the muzzle and around the eyes in horses with white markings or in certain types of breed such as Appaloosas.

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Sun burn can happen due to simple excessive exposure to sunlight, but can also indicate other problems. Sun burn is more likely to occur when a horse is exposed to St John’s Wort (ragwort) because when eaten, pigments from the plant are absorbed and react with sunlight causing ‘photosensitisation’, where pink skin becomes seriously sunburnt under normal exposure to sunlight.

Sun burn can happen due to simple excessive exposure to sunlight, but can also indicate other problems. Sun burn is more likely to occur when a horse is exposed to St John’s Wort (ragwort)

Photosensitisation can also be a sign of liver disease. It is more likely to occur when the function of the liver is compromised. It is difficult to distinguish between photosensitisation and sunburn in horses, but if your horse shows signs of sunburn under normal exposure to sunlight, it is prudent to rule out other potential causes.

Sunburn can be prevented by the application of horse safe sunblock. Avoiding sun exposure is another effective way of minimising risk. Only turn out on overcast days or avoid periods of high exposure by restricting turnout to early morning and late evening only, avoiding the middle part of the day.

Sun damage and squamous cell carcinoma

Squamous cell carcinoma (SCC) is the second most common form of cancer in the horse. SCC is thought to develop in response to the damaging action of ultraviolet light in areas where there is no protective skin pigment or hair. Chronic skin irritation and possibly viral infections may also be contributing factors. The most common risk factor is the pattern of skin pigmentation – pale areas are susceptible – and the most common location is the skin around the eyelids, closely followed by the third eyelid. These are areas of high sun exposure.

Squamous cell carcinoma (SCC) is the second most common form of cancer in the horse. SCC is thought to develop in response to the damaging action of ultraviolet light in areas where there is no protective skin pigment or hair.

There is no gender predisposition to these tumours. Breeds with little pigment in these areas, such as Appaloosas and Quarter Horses are however predisposed. Interestingly, squamous cell carcinomas are also fairly common on the penis, which is not an area that is typically exposed to sunlight. The reasons for this are unclear, but a viral cause has been suggested.

These lesions often have a characteristic appearance, resembling a very small pink cauliflower. However they can also look like an ulcer, an unusual pink area, or a crusty, non-healing wound. Any horse with a suspicious skin lesion should be examined by their vet. Horses with non-pigmented skin around their nose or eyes should be protected from the sun to reduce the risk of developing SCC; there are UV protective eye masks and special sun creams available which are advisable for any horse at risk.

How can we treat an SCC?

Traditionally, SCC is removed by surgical procedures. This can be an effective treatment, but recurrence or sometimes even spread of the tumour can occur. Other treatments are often given alongside surgical removal (or instead of surgery if this is not possible). These are usually topical chemotherapy agents that are applied onto or injected into the tumours, or radiotherapy. Radiotherapy has several advantages over topical treatments, and is now available at the Animal Health Trust.

The most effective form of radiotherapy for most SCC is called strontium plesiotherapy. Strontium plesiotherapy involves the direct application of a radioactive source to the tumour surface. The major advantage is that the type of radiation emitted penetrates only a few millimeters. This means that a large dose of radiation can be applied to the surface without adversely affecting deep tissues. This means that the tumour tissue is destroyed, but delicate surrounding structures (such as the eye) are not affected.

Strontium plesiotherapy has been successfully used in the treatment of tumours located in many difficult areas in dogs, cats, and horses and represents a real advance in the treatment of these lesions. Strontium may be performed under standing sedation in some locations, and under a short general anaesthetic for others. Depending on the size of the tumour, treatments are usually given in 3 sessions, spaced 48 hours apart. Each treatment takes around 5-10 minutes depending on the size of the area being treated. Between treatments the horse can be treated as normal. This treatment is suitable for both tumours that cannot be surgically removed and those that have been removed. The procedure can also be used to treat some other types of skin cancers in the horse.

Prevention is better than cure

As with all conditions, prevention (where possible) is better than cure. If your horse has pink skin, take precautions to avoid excessive sun exposure: use sun block on these areas to help prevent sun damage and avoid exposure to the sun during the middle of the day to reduce the risk of sunburn and the development of SCC.

For more information on the Animal Health Trust visit www.aht.org.uk

If you are in any doubt over your horse’s health we recommend you seek help from your registered veterinarian.