While driving cross country in between calls I have noticed from the road a few cattle beginning to show evidence of lice infestation. Cattle, horses, sheep, goats and swine are all susceptible to parasitism from lice. Interestingly enough, lice are species specific meaning that there is a particular species of louse that prefers feeding on a specific species of livestock. Furthermore, in each species of livestock there are two types of lice that may be observed. Biting lice feed on dead skin cells and other debris from the surface of the skin. Sucking lice feed off of the blood. All species and types of lice cause skin irritation and in rare instances sucking lice may cause significant anemia.
Lice are an external parasite and with careful inspection, can be visualized with the naked eye. Infested animals are frequently seen rubbing and scratching or constantly licking themselves. Heavy infestations cause hair loss often in patches around the neck, topline and tailhead. Infestation can occur at any time of the year, however, seasonal outbreaks are most common with the highest numbers of lice found in late winter and spring. Reproduction in the louse is most efficient in cooler weather. Therefore, little multiplication occurs during the heat of the summer but reproduction then picks up in the fall leading to high numbers of lice in late winter and spring.
Lice infestation undoubtedly impacts the productivity of livestock but, with the exception of extreme infestations, generally does not have a real significant impact on weight gains. Milk production in dairy cows may be more easily influenced by lice infestation in comparison to weight gain in meat animals. In all species, significant animal discomfort and restlessness is a primary concern.
Lice complete their entire life cycle on the host animal. They can spread from one animal to another either by direct contact between individuals or by indirect transmission such as on shared brushes, combs or horse tack. Many topical parasiticides are available for treatment either in the form of a pour-on application, a powder or a dip. Oral or injectable avermectins (such as ivermectin or moxidectin) are efficacious against sucking lice but not biting lice. Due to the risk of transmission from one animal to another and the fact that one heavily infested animal often suggests the presence of more mild infestations in other animals in the herd, treatment of the entire herd at one time is recommended versus treating individual animals. Furthermore, repeating treatment in 2-3 weeks is also advisable. Many treatments are not efficacious against louse eggs, leaving the potential for a relapse if retreatment is not applied.
Dr. Darren Loula, DVM, is owner of Christian County Veterinary Service, LLC, a mobile large animal vet clinic.