By Kentucky Equine Research

Just as humans can be burned by the sun’s ultraviolet rays, light coloured horses may suffer from sunburn. Even horses with dark coats can be vulnerable to sunburn if they have white markings on their faces or legs.

Sunburn is seen most often in spring and early summer when longer periods of sunlight coincide with shedding of winter hair. Skin around the eyes, top of the tail, muzzle, and ear tips may become reddened and may swell, blister, or peel in severe cases.

Protect your horse from sunburn by turning him out in the early morning or late evening, providing ample shade, and applying sunscreen, fly masks and sheets.

Help your horse avoid sunburn by following these precautions:

• Keep horses stalled during the hours of most intense sun and avoid turning horses out without access to shade.
• Use a child-safe, human sunblock preparation on areas that are likely to burn. Be careful not to get sunblocking products in the horse’s eyes. Apply to a small area first to check for skin reactions before applying to a large area of the horse’s skin.
• Reapply sunblock regularly. Horses that are grazing may need frequent applications because creams will be wiped off on tall grass. Some products come in a range of bright colors, which will make it easier to see when it’s time to put on more cream. A number of shampoos, fly sprays, and coat conditioning products include a sunblock but may not contain enough screening to be effective. Check labels for sun protection factor (SPF) claims. The higher the SPF number, the better the protection.
• Look for a fly mask with extensions that cover the ears and most of the muzzle. For light-skinned horses with thin coats, consider turning out in a light cotton sheet or summer fly sheet that offers UV protection.

Alsike clover grows 30 to 75 cm in height with a small, half-inch diameter pale pink or whitish flower which forms at the ends of secondary branches from the main stem. Found in fields and on roadsides, the plans blooms from April to October.

Danger in the Grass

Common pasture plants may trigger sunlight hypersensitivity in horses, making them much more likely to develop serious skin damage after sun exposure.

Primary sensitization occurs when sunlight reacts with plant toxins circulating in capillaries near the skin’s surface.

Ingestion of other plants, as well as some molds and mycotoxins, can cause liver damage, one sign of which is increased skin reaction to sunlight; this is known as secondary sensitization.

Some plants can cause both types of reaction.

 Alsike clover, a wild strain of clover with white or pinkish blossoms, is one of the most common culprits.

Alsike clover flower.

It grows well in wet weather, spreading quickly through fields that do not have vigorous stands of pasture grasses.

When only a few plants are present, they may be removed by hand or by selective spraying.

If grazing areas are heavily infested with these plants, complete renovation of the pasture may be the only way to remove undesirable vegetation.

Among the other plants that cause photosensitization are St. John’s Wort, bishop’s weed, spring parsley, and wild buckwheat.

 St. John’s Wort is particularly difficult to eliminate, as it spreads both by seed and by underground rhizome.

A bushy perennial plant, St John’s Wort can grow up to a metre in height, with yellow flowers from mid to late summer. Flowers measure up to 2.5 cm with five petals and clusters of feathery gold stamens.

Its resistance to standard herbicides has led to the development of effective biological control methods including the use of beetles, moths, and midges that feed on the plant’s foliage and flowers.

In some cases, signs of photosensitivity may not show up for several weeks after a horse has eaten alsike clover or another dangerous plant.

Because the toxins are not destroyed by drying, hay made from any of these plants may cause a reaction long after pastures have stopped growing.

Horses that have been treated with tetracycline and some other drugs may also develop hypersensitivity to sunlight.

Sunburn caused by plant ingestion or veterinary treatment is likely to be much more extensive and severe than simply reddened skin.

St. John's Wort flowers.

Resources

Agricultural agents have the knowledge to identify dangerous plants in pastures or in hay. These experts can also advise on the most effective way to rid fields of unwanted vegetation.

Tack shops and equine supply outlets offer a selection of sunblock products, fly masks, and turnout sheets to protect horses against insects and excessive exposure to sunlight.

Horse owners should get veterinary advice if their horses develop serious reactions to sun exposure. Treatment may be needed to relieve pain and prevent infection. Especially in a horse that has never shown much sensitivity to sunlight, a sudden or severe skin reaction may be a sign of liver disease or damage, and early intervention by a veterinarian is critical in returning the horse to health.

Main article photo: Horses can get sunburn just like humans can. Light coloured horses and horses with areas of pink skin (white hair) are the most at risk.

This article was published in the June 2011 issue of Canadian Horse Journal.