Cold winter temperatures can create an ideal environment for a lice infestation in stocker cattle. Cattle lice are small, but they occur by the thousands, or even tens of thousands, on infested cattle. The economic impact of lice is highly variable and does not always correlate with the severity of infestation.

Cattle damage fences, and bruise and scrape themselves as they rub to relieve itching caused by the lice. Louse-infested animals are under stress and may be predisposed to disease. Blood loss from sucking lice is sometimes severe enough to cause anemia.

To reduce lice problems, treat animals twice on arrival, two to three weeks apart. The first treatment kills the adults, and the second treatment kills the adults and nymphs that were eggs during the first treatment. It is critical to keep infested animals away from treated animals.

A second option is to treat animals early in the fall and again in early winter, such as November through February. This plan suits the management system of many cattle herds and stocker operators, and it keeps lice populations to manageable levels. However, the animals will not be entirely free of lice.

The five species of cattle lice found in North America include four that feed by sucking blood. The fifth species feeds on skin tissue of cattle.

All cattle lice spend their entire lives as parasites on living cattle. When removed from the cattle, they live a few days at most. The females lay eggs, which they glue to individual cow hairs close to the skin of their host. Immature lice are called nymphs. Each nymph sheds its skin three times as it grows to adulthood. Nymphs resemble adults of the same species in feeding habits and appearance.

Maturation to adulthood is approximately three weeks in cool weather. If a female louse lays eggs (called nits) on the hair of an animal today, they will hatch in the next three to seven days. Once hatched, the nymphs can start laying eggs in approximately two weeks. The adult females lay about one egg per day for two or three weeks.

Knowing the lifecycle is important because products available today kill only the nymphs and adults, having no effect on the eggs. One infested animal may not have many nymphs or adults at the time of treatment, but when the nits hatch at a later date, they may not be killed by the treatment product. Additionally, it is important to remember that pour-on products applied to an animal’s back may not reach the lower brisket, armpits and groin. Therefore, to get adequate lice control for an entire season, producers should apply two doses of product approximately two weeks apart. Also, it is absolutely necessary that no untreated animals be allowed contact with the treated animals.

For more information about treating lice, call Bayer Animal Health 1-800-633-3796.