Lice are tiny external parasites found on many types of animals. Sucking lice feed off the blood of their host, while chewing lice feed on skin and hair.
In horses, one type of sucking louse (Haematopinus asini) and one type of chewing louse (Damalinia/Bovicola) equi) are well recognized.
Lice are typically more of a nuisance than any sort of serious health threat. However, the presence of a very large population of blood-sucking lice can result in significant blood loss (anemia). Chewing lice can cause intense irritation and itchiness.
Signs observed in a skin sensitive horse can include: itchiness, rubbing, biting at skin, hair loss, unthrifty appearing coat, and potentially even open sores that result from intense scratching.
It is important to know that lice infestation usually is only seen in horses that have other underlying health problems, especially under-nutrition. Lice are far more commonly found on stressed or immune-suppressed animals. Lice infestation is more common in the winter months, probably due to a longer winter hair coat.Management problems (overcrowding, poor parasite control), and underlying illness are all predisposing factors.
Healthy, well groomed and well-fed horses are rarely affected by lice.
Lice are small (2-4 mm) and slow moving. You might see them if you part the hair coat and carefully examine the skin with good light. Eggs may also be seen glued to hairs. Lice are most commonly found on the head, neck/mane, rear end and tail base.
Transmission: Lice are considered species-specific. Infestation should not spread from a horse to a human or another species of animal. Transmission between horses requires close physical contact. That said, lice may live a few days off of the host and can be spread by grooming equipment or housing horses in stocks, stalls, or trailers that other horses have recently occupied.
Clipping and more frequent bathing may help control re-infestation. There are a variety of sprays, dusts, and wipe-ons approved for louse treatment in horses. Talk to your veterinarian about the best product to use.
Insecticide treatment should be repeated at least twice at a 2 week interval to account for the full life cycle of the louse (30-45 days from egg to adult).
Other Diagnoses Considered
Prognosis & Relevant Factors
The prognosis for louse infestation is good in an otherwise healthy and well-managed horse. To successfully treat horses that have lice secondary to an underlying disease, the underlying disease needs to also be treated effectively.
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