It is common for groups of young horses housed together during winter months to become infested with lice, as large numbers multiply unnoticed in their long winter coats.
There are two varietis of lice: bloodsucking and biting. Both species are six-legged, tiny, wingless and usually light brown in colour.
The sucking variety is the larger of the two and is quite easy to spot during routine inspection. They have pointed heads and penetrate the skin with their mouth parts. They are commonly found on the longer hairs of the mare, tail and fetlocks, where their eggs (nits) are visibly attached to the hair.
The “biters” live close to the skin on scurf and dead cells, so are harder to see. They are generally found along the back and sides of the horse, but may spread over the entire body if untreated.x
Lice are extremely irritating to the horse, which may rub or bite itself, causing sores or quite major skin damage. Heavy infestations will cause hair loss and the sucking type may consume enough blood to cause anaemia in the horse.
Infected animals can look rather moth-eaten and may rub their tails as well as their hindquarters. Some severely affected horses do not do well, and lose condition.
Lice are generally transmitted by direct contact between horses, but can survive for a few days in rugs, grooming brushes and tack, so may be spread in this manner.
Vet Karen Coumbe says: “Lice are often forgotten in an itchy horse. There is a tendency to think they are not there if they are not visible. Also the assumption that a one-off treatment will have got rid of them is not correct.”
Treatment for lice infestations varies. Historically, powerful whole body washes and powders were available, but these contained compounds which had health and safety implications and have been discontinued.
Some current proprietary louse powders and spot treatments can have an unpredictable and often disappointing efficacy. While some wormers will reduce the extent of egg laying by lice and mites, a topical treatment is often needed as well. It is sensible to discuss treatment options with your vet.
Theoretically, treatment should be applied simultaneously to all horses in contact, and repeated regularly to kill off the hatching nits.