Lice are ectoparasites that live on the skin and in the fur of animals that are typically over-crowded and/or stressed and seen in animals living in unsanitary conditions. There are two types of lice and the distinction is how they feed. One type feeds through biting and chewing on hair and dead skin and the other feeds through sucking the blood of the host animal.
What Are Lice?
Lice are tiny parasitic insects that live in the hair coat of horses or other mammals. Lice are species-specific, meaning that bird lice generally won't live on people or dogs, horse lice don't typically infect people. You're not likely to get lice from your horse or pass them on to your cat. Lice infestations can be but are not necessarily an indication of poor care and/or poor nutrition. 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 lice are transferred from horse to horse by direct contact or through shared brushes, blankets, and equipment.
Signs of Lice on Horses
- Irritated skin
- Visible raw patches on the skin
- Rough hair coat
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 that it 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. If the horse is infested with the sucking louse, blood loss may be severe enough to 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. Additionally, lice prefer dark and avoid bright sunshine.
- Physical contact with another lice-infected animal
- Using equipment or tools that are lice-infected
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.
Typically, horses that are underweight or in poorer condition are more susceptible to lice infestations. Horses in good health have a stronger immune system and can usually fight off an infestation unless they are housed in stressed or poor conditions.
The first step is to treat the horse itself with either a topical de-lousing powder or a veterinarian-administered louse medication. Common treatments are permethrin-based dust, shampoos, or rinses. Be cautious with applying treatment to any skin that may be irritated as that can cause further problems. When applying any medication powder, take care not to inhale it, and to wash up after you apply it. When using the 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.
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.
Your veterinarian is your best resource for what to use when tackling lice problems.
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. In a busy barn, it's a good idea that each horse has its own brushes and equipment because shared grooming tools and blankets can spread many skin problems including lice, ringworm, and mange.
Lice Of Horses. Veterinary Manual
Lice On Horses. Ontario Ministry of Agriculture Food and Rural Affairs
Controlling Lice In Horses. Kentucky Equine Research
Castilla-Castaño, Eloy et al. Control Of Lice Infestation In Horses Using A 10 Mg/Ml Deltamethrin Topical Application. Irish Veterinary Journal, vol 70, no. 1, 2017. Springer Science And Business Media LLC, doi:10.1186/s13620-017-0100-2
Lice and Your Horse. Canberra Equine Hospital, 2020