Lice on Horses

Diagram of a horse louse.
Diagram of a male and female horse louse. Credit: G. F. Ferris. San Francisco: Pacific Coast Entomological Society, 1951

Lice are well-known parasites that live on animals. There are two types of lice species and the distinction is how they feed. One feeds through biting and the other feeds through sucking. While lice may be associated with dirt and poor living conditions, that's not always the case. It isn't unusual for the most well-kept race or show horses to get lice. The difference may be that the infestation is caught much sooner in the show horse, preventing the lice infestation from becoming a serious health problem.

What Are Lice?

Lice are tiny parasitic insects that live in the hair coat of horses or other mammals. Lice are species specific, and that's why bird lice generally won't live on people or dogs. And you're not likely to get lice from your horse or pass them on to your cat. However, given the right species, lice live anywhere they can find a warm home and a meal. Lice infestations are most often, but not necessarily an indication of poor care. However, even very healthy horses can get lice. They can be common in stables like racing stables, where close quarters and shared equipment make the spread of lice easy. 

Lice are flat-bodied insects. When they are fully grown, they are only 2 to 4 millimeters in length. In horses, they tend to breed in the thick coats that the horse will grow during the winter months. They can live in all over the horse's body, including the mane, tail, and coat.

The two species of lice that impact horses are Haematopinus asini (H asini), the horse sucking type, and Damalinia equi (D equi), the horse biting type. Both types of lice are seen around the world. The only type of louse that favors another species is those found on poultry and these very occasionally affect some horses. The lice are transferred from horse to horse by direct contact or through shared brushes, blankets, and equipment.

Symptoms of Lice in Horses

Depending on the type of lice, the parasites will either suck the horse's blood or feed off of dead skin cells. The lice lay eggs called nits in the horse's hair coat and mane. These nits will hatch into nymphs that mature into egg-laying adults. Both nymphs and adults will cause the itching associated with lice. The horse will be intensely itchy, especially around the base of the tail, mane, and head, although the lice may be all over the horse. As the horse tries to relieve the itching by rubbing itself on fences, trees, or stall walls it can rub raw patches into its skin. It's possible for a horse to be so uncomfortable, they will appear listless or colicky.

Sometimes, one or two horses within a herd will be more infested than the others. The others may or may not have lice, but the individuals that the lice seem to like will be more affected. A horse that is very badly infested with lice will become very run down and the blood loss may actually cause anemia. Winter and early spring are when lice are most evident, as the horse has a long hair coat for the lice to live in. Lice don't like the sunshine, so they may disappear in the summertime.

Treatment of Lice

Knowing whether the lice are the dander snacking or blood-sucking variety will help to determine what treatment to follow to get rid of them. Sucking lice are gray, whereas chewing lice are brownish. You will be able to see the lice and their nits in the horse's hair although you might not be able to see their color without a microscope.

The first step is to treat the horse itself with either a topical powder or a veterinarian administered medication. Common treatments are permethrin based dust, shampoo, or rinse. Be cautious with applying treatment to any skin that may be irritated as that can cause further problems. The powder to treat lice is relatively innocuous, but it's still a good idea to try not to inhale it, and to wash up after you apply it.

All equipment that could carry lice or nits must be washed as well. Blankets and washable equipment can be laundered and dried with high heat, or boiled. When using powder, it's important to make sure the powder penetrates right down to the horse's skin. Wear gloves and a dust mask to avoid contact with the chemicals.

If chicken lice are the problem, the chickens and the horses should be kept separately, and the area where they both lived should be cleaned well. Treatment may have to be done several times to kill all the lice and you may want to treat horses that don't appear affected so that no lice move to the healthier horses. Natural treatments include oils, which are thought to suffocate the nits and lice, and sulfur, which is dusted on and worked into the hair. Sulfur repels the lice but doesn't kill them, so the treatment needs to be done very frequently. Your veterinarian is your best resource for what to use when tackling lice problems.

Prevention

During the winter months when your horse has a long coat, brush frequently to remove dander and check under any blankets frequently. If you bring a new horse home, it should be kept separate from other horses to see if there are any problems that might get passed on to the resident herd. It's a good idea that each horse has their own brushes and equipment because shared grooming tools and blankets can spread many skin problems like lice, ringworm, and mange.