Horses occasionally get lice, and a horse owner needs to know what to look for and how to treat these irritating parasites. Bill Clymer, PhD, of Amarillo, Texas (now a livestock parasitologist on the professional services staff of Fort Dodge Animal Health), has worked with horses and lice for many years. Earlier in his career, he was an extension livestock specialist with Texas A&M University. We also talked to Jack Lloyd, PhD, professor of entomology at the University of Wyoming; and Sandy Gagnon, extension specialist at Montana State University, for this article.

Sucking louse

There are two types of lice that affect horses–sucking lice (above) and chewing lice (below)–and three species. All three live throughout the United States. The sucking lice are probably more damaging because they can create anemia due to blood loss (resulting in weakness or stunted growth in young animals), but chewing lice may be more irritating because horses have very sensitive skin.


Lice occur most often in horses that are stressed, Clymer says, by inadequate nutrition, a severe winter, illness, injury, etc. “For 20-some years I had my own research company, doing research on parasites. I’d buy cheap horses that were in poor condition for various research studies, and they’d be