By E.O’Flynn MRCVS

It is that time of year again when many horses become infested with lice. Infestations usually occur in the Winter months when the coat is long.

What types of lice affect horses?
There are 2 types of lice that affect horses. (a) Damolinia Equi is a biting louse that feeds on scarf and other debris in the skin surface. (b) Haematopinus Asini is a sucking louse that feeds on the blood and tissue fluids of the horse.

Do horse lice live on humans?
Fortunately, horse lice are host specific and do not live on humans.

What is the method of spread?
Lice are spread from one animal to another by direct contact. They could also be spread by shared rags and brushes. In this case the louse eggs may be transferred from one animal to the next. Lice themselves would not be transferred unless the brushes or rags were used immediately by the other horses. The reason for this is that the lice only survive off the horse for approximately 20 minutes. Lice do not live or survive in a stable or on tack.

Can lice be seen on the horse’s skin?
Yes. Close examination by a veterinary surgeon or a reasonably knowledgeable horseman will detect the presence of the lice. By turning the hair sideways they may be seen moving on the skin. The are 1mm to 3mm long and grey in colour. Use of a magnifying glass may help to identify the lice. The eggs also known as “nits” may be seen close to the roots of the mane and forelock. What are the signs of louse infestation. Lice cause the horse to become very itchy. Horses tend to bite themselves and rub off any objects which are available to them. Bald sore patches may result on the horse’s skin when the rubbing and biting are done excessively. The coat may become dull and scurfy. Loss of condition in severe cases. Some horses may become restless and roll regularly to relieve the itch. In chronic cases the skin eventually becomes thickened.

What is the treatment?
1) Louse powder.
2) Antiparasite washes. These should be well distributed and evenly spread over the body. It is important to give a second dressing about 10 – 14 days later to kill the new young lice that have hatched from the eggs since the first treatment. These dressings do not kill the eggs.

Do any of the worm doses kill lice?
No. Many horseowners are under the false illusion that these pastes especially the ivermectin ones also kill lice. This is not the case.

Do cattle ivermectin injections work in horses?
They can be used, but it is inadvisable. They are not licensed for horses and therefore carry certain risks, i.e. they may kill the lice but could also kill the horse, not a great outcome. Cattle pour-ons and sheep dips also carry risks when used in horses.

When treating horses for lice it is important that all horses in the paddock are treated. If even one is left untreated, it may act as a resevoir for the lice and re-infest the others at a later stage. Be careful when using shared rugs, tack and brushes as this could transfer the lice from one stabled horse to the next.

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