Lice are small flightless insects that live in the feathers or hair of animals and people. All lice live within the environment provided by the skin and its hair or feathers. They move from host to host, primarily by direct contact. In temperate regions, lice are most common during the colder months.

There are 2 basic types of lice. The largest group is the biting or chewing lice (order Mallophaga). The smaller group is the blood-sucking lice (order Anoplura). Two species of lice can infest horses, Haematopinus asini, the horse sucking louse, and Damalinia equi, the horse biting louse. Normally, the horse sucking louse is found at the roots of the forelock and mane, around the base of the tail, and on the hairs just above the hoof. The horse biting louse prefers to lay its eggs on the finer hairs of the body. It is found on the sides of the neck, the flank, and the base of the tail.

Females glue their eggs, known as nits, to the hairs of the host near the skin. Ordinary shampooing and washing will not dislodge the nits. Nits are pale, translucent, and almost oval in shape. Once the nits hatch, the lice go through 3 nymph stages before reaching adulthood. The nymphs look very much like adult lice, only smaller. It takes about 3 to 4 weeks for most lice to go from nit to adult, although this period varies with the species.

Lice can be found anywhere on the body, but they are more commonly seen on the head, neck, mane, and the base of the tail. The first signs that your horse may be infested with lice are biting at and rubbing infested areas. Hair loss and even skin loss may occur. If the lice are abundant, the hair might also be matted. Sucking lice cause small wounds that can become infected. Usually, diagnosis is made by visual observation of lice on the infested animal. Parting the hair often reveals the lice. Chewing lice are active and can be seen moving through the hair.

Horses can be treated with sprays of permethrin, coumaphos, or malathion to kill lice. A wipe-on formula is also available and is especially useful for treating horses that react to sprayer noises. Your veterinarian can recommend an appropriate control product and provide directions for its use. Reapplication may be necessary to kill all lice.

The lice that infest horses are not normally attracted to humans. Therefore, while care in dealing with the lice infecting your horse is recommended, owners should understand that people rarely get lice from their horses.

Last full review/revision July 2011 by Karen A. Moriello, DVM, DACVD; Carol S. Foil, DVM, MS, DACVD; John E. Lloyd, BS, PhD; Bertrand J. Losson, DVM, PhD, DEVPC; Wayne Rosenkrantz, DVM, DACVD; Patricia A. Talcott, MS, DVM, PhD, DABVT; Alice Villalobos, DVM, DPNAP; Patricia D. White, DVM, MS, DACVD; Thomas R. Klei, PhD; David Stiller, MS, PhD; Stephen D. White, DVM, DACVD