There’s nothing sweet about sweet itch. This horrible skin condition, a bit like human eczema, causes horses to bite, scratch and rub at their skin. Sometimes it can trigger a reaction so violent that the horse can cause severe damage to itself or its environment.
There are a number of possible causes for sweet itch in horses, including feed hypersensitivity and nettle stings. However, the likely culprit is the tiny but mighty Culicoides midge, a pesky little flying nuisance that thrives during warm, wet summers.
A study in Switzerland of 42 sweet itch cases found up to 10 specific midge salivary proteins responsible for making affected horses itch in certain areas. The part of the horse’s body that is affected tends to be linked to the midge’s biting habits; but the tail base, neck and mane and ventral abdomen are all among the most vulnerable areas.
Some breeds of horse are genetically more prone to this type of insect allergy than others — cob types are more likely to be affected than thoroughbreds — but that’s not to say that any are exempt from sweet itch. Just like people who suffer an allergic skin reaction, individual animals have different tolerance thresholds and sometimes the desire to itch and rub is so intense that the constant pressure on the area can mean that it then becomes infected, making the problem even worse.
Culicoides midges thrive in marshy, boggy fields, so the first line of defence is to avoid these habitats. It is therefore advisable (although not always practical) to relocate a horse that is susceptible to sweet itch to insect-free areas such as exposed, windy fields or chalk-based grassland. Grazing should be well drained and away from rotting vegetation such as muck heaps, which may attract flies and water troughs should be cleaned regularly to prevent flies from breeding there.
Insect repellents and insecticides may help control midges, especially those containing pyrethrins or pyrethroids, which often have to be applied either weekly or fortnightly. These should, however, be used with care.
Holly, a 12-year-old Welsh section D, suffers from insect hypersensitivity and sweet itch. Her owner, Sophie Hill, adapts the mare’s routine accordingly.
“She comes into the stable at dawn and dusk when the midges are at their worst, and she wears a bug rug all the time in the spring, summer and autumn — it only comes off when she is ridden,” she says.
Hill also puts a fan in Holly’s stable to help ward off unwelcome flying visitors. “Midges prefer still conditions — they don’t like wind — so the fan really helps,” she explains. “If I take all the right precautions, I know that I can make Holly’s life a lot more comfortable. Most of the time you would never know that she has a problem.”