One of the most common is the cattle-chewing louse, Bovicola bovis. This species is about 1/8-in. long when fully grown, has a yellow-brown appearance and is most commonly found on the animal’s neck, back, hips and tailhead.
B. bovis are not blood feeders, but they use their mouthparts to rasp away at animal skin and hair.
In addition to chewing lice, sucking lice feed on the blood of dairy cattle. Common species include the long-nosed cattle louse (Linognathus vituli), short-nosed cattle louse (Haematopinus eurysternus) and little blue louse (Solenopotes capillatus).
Sucking lice have mouthparts specialized for penetrating animal skin. They spend most of their time with their heads firmly attached to the skin. These lice often take on a darker appearance than chewing lice as they become engorged with blood.
Female lice lay their eggs by attaching them to hairs with a strong glue to prevent them from falling off. The eggs, known as nits, hatch in 10 to 14 days, and the young lice (nymphs) complete their development within several weeks.
Lice, in contrast to some other livestock pests, are permanent parasites that spend their entire lives on the host animal.
All four types of lice cause extreme annoyance to the host animals. Milk production declines in heavily infested cattle, and the animals’ preoccupation with rubbing leads to hair loss, reduced feed conversion efficiency and general unthriftiness.
Infested animals become irritable and difficult to work with, especially during milking. People working around lousy animals are exposed to greater risk of injury and are also annoyed by stray lice they pick up from infested animals during handling.
Although louse problems are generally perceived as being most severe during the fall and winter months, animals of different age groups show distinct differences in the seasonality of infestation.
Lice are most common on mature cows in December through March, with peak populations found in March.
In contrast, calves housed inside barns show high levels of infestation later into the spring, with peak populations in June. This difference may be due to the fact that cows are placed on pastures in the spring, where exposure to direct sunlight heats the skin to levels lethal for most lice.
Calves kept in the cool environment of the barn are not able to take advantage of sunlight’s natural curative properties.
Other animal housing conditions also affect louse populations. Cows in stanchion barns are twice as likely to be infested as cows in freestalls, owing to the greater opportunities of unrestrained animals to groom themselves.
Calves housed in communal pens inside barns are 10 times as likely to be infested as calves in individual hutches. The effectiveness of hutches results from a combination of the animals’ isolation from one another and the opportunity for calves in hutches to spend time in direct sunshine.
See our upcoming story on successful louse monitoring and management strategies in dairy cattle.