Lice are very egalitarian when it comes to whom they like to live on. Whether it's head lice on humans or horses, they don't care if you inhabit a mansion or a shed, they're glad to hitch a ride and grab a meal on anyone they can. 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 between those rich horses and the poor horses we would associate with having lice is that the infestation is caught much sooner before the lice infestation becomes a serious health problem.
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 but are a good way to scare your city cousins with when they pick up a pet chicken. 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.
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.
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. Sometimes horses can 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.
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 get work the powder 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 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 ‘jump ship'. 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.
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 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.