By Susan Donaldson

Clyde Vet Group

Feather mites – or chorioptes equi to state their correct name – are the cause of a great deal of frustration and irritation to both horses and owners alike.

These mites live on the surface of the skin and feed on dead skin cells. Heavier-type horses and ponies with a good amount of feather provide an ideal environment for them as the dense hair traps scurf and cells and protects the mites from any extreme temperatures.

The main signs of infestation with feather mites are associated with itchiness – stamping of the hind limbs is a particularly common clinical sign and some horses will bite at their limbs or find other objects like fence posts to scratch on (Fig 1).

The wounds and broken or thickened skin, which is seen on the legs of affected horses, are actually a result of the self-trauma from the itchiness as opposed to the mites themselves. If left untreated, the skin of the lower legs can become thickened and form deep folds particularly on the back of the pasterns (Fig 1). The back of the knee is also a common site for infection.

The chronically damaged skin then becomes susceptible to bacterial and yeast infections, maintaining a cycle of irritation which is very difficult to break.

Diagnosis

It is possible to confirm the presence of chorioptes mites by taking brushings of the coat, or taking samples by sticking selotape to the limbs and examining these samples under the microscope, In reality, however, these techniques are not very sensitive at detecting the mites and so generally the diagnosis is made on the basis of the horse’s appearance, history and clinical signs.

Some horses may be heavily infested without showing many clinical signs, whilst some appear to react very strongly to the presence of only a few. It is thought this may be due to some horses having an allergic-type reaction to the mites.

Treatment

There are few medications which are licensed for use in the horse and effective against this condition.

‘Off-licence’ treatments include topical Frontline spray (fipronil) and injections of doramectin. A topical shampoo, LimeDip Plus, with the active ingredient sulphur, is licensed for use in horses and can be very useful as in addition to being anti-parasitic, it is also anti-fungal, anti-fungal and breaks down the dead skin cells the mites like to feed on.

Unfortunately, there has been a manufacturing issue with this product. Clipping of heavy feathers is not absolutely essential, but it should be considered as reducing the haircoat will immediately reduce the number of mites on the limbs and if there is significant damage to the underlying skin, removal of the hair will facilitate the treatment of any wounds or broken areas of skin.

No single product is effective at killing 100% of mites and so it’s likely that several different products may require to be used, sometimes simultaneously to get the best result. Speak to your vet about what may be most practical and effective for your horse.

In addition, severe cases may need other medications, such as antibiotics or even steroids, to deal with the secondary trauma as a result of the intense itching. Do not underestimate how painful these horses can be! Many who are badly affected will react strongly to their limbs being touched or washed and so sedation may be required.

Mites are mostly spread from horse-to-horse via direct contact. The mites have a life cycle which lasts around three weeks, but they can survive in the environment away from the horse for up to 69 days, meaning that other horses could become infected as a result of coming into contact with contaminated bedding or other materials.

This represents a real challenge for treatment, especially in the livery yard scenario where there are likely to be many different horses and owners.

Where possible, the environment should be thoroughly disinfected at the time of treating the affected horse and the treatment of in contact horses, even those showing no outward signs, should be considered.