Keeping a happy horse during the summer months can be a challenge! Many horses become itchy, particularly the top of the tail and the mane. The itching can be bad enough that your horse rubs on anything available, rubbing away hair and even skin. Itching issues occur mainly during the summer months but mild springs and autumns can also be problematic.
In the UK, several species of the Culicoides midge and, to a lesser extent, the larger, hump-backed Simulium Equinum, a member of the blackfly family, are responsible for intense irritation in horses. Different midges have preferred feeding sites; Culicoides tend to be body feeders and the Simulium ear feeders. Culicoides adults mainly rest among herbage and are most active in at dawn or dusk in calm conditions. Breeding sites are commonly in wet soil or moist, decaying vegetation. They are tiny, with a wing length less than 2mm, and are able to fly only a short distance (100m or so). They do not fly in strong wind, heavy rain or bright, clear sunshine. They dislike hot, dry conditions. The grey light at dusk and dawn suits them well, and they are at their most active at these times. Normally, when bitten by a midge, the horse’s immune system recognises a foreign protein and reacts to eliminate the substance. In horses the immune system overreacts, in the same way hay fever sufferers overreact to pollens. This is known as a type one hypersensitivity reaction.
The result is itching at the site of the bite. The itching causes the horse to rub and scratch away the tail, mane and parts of the coat, posing more problems.
Hereditary predisposition may be a factor and scientists have identified several genes that make individual horses more susceptible. However environmental factors play a major part – where the horse is born and where it lives as an adult are at least as significant as the bloodlines of its sire and dam. Exposure to midges during early years of life appears to be important in helping young horses become tolerant to the proteins present in midge saliva. If these proteins are not recognised by the horse’s immune system as being harmless, problems occur.
Measures should be taken to stop a horse being bitten and reacting. Wherever possible, susceptible horses should be moved to pasture away from trees, nettles and rotten vegetation, such as muck heaps and leaves; chalk-based grassland is better than heavy, clay pasture. Pasture on a hill with more wind is preferable. Turnout at dawn and dusk should be avoided. Ideally turn out if it is windy, there is heavy rain or bright, clear sunshine and hot, dry conditions. Fly screens can be fitted to windows and doors, and protective rugs help reduce the biting.