February 2012 Articles

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Controlling Lice on Your Cattle

Controlling Lice on Your Cattle, Dr. Jeremy Powell, Associate Professor, and Dr. Chris Tucker, Program Associate

Even though other external parasites such as flies and ticks are not a problem this time of year, you still need to be on the lookout for signs of lice in your cattle. This problem usually starts in the late fall and builds throughout the winter months. If you have noticed your cows standing around scratching on fence posts, trees or the hay feeder, then they may be infested with lice. Typically, cattle affected by lice have rough hair coats and noticeable patches of hair loss around their face, neck, back, sides or tailhead. Infested cattle may also appear unthrifty and have a poor physical condition. Heavy infestations can reduce gain performance and have a negative economic impact on cattle.
Two different types of lice typically affect cattle. One is known as chewing or biting lice, and the other is sucking lice. The sucking louse has a long mouthpart used for sucking blood from infested cattle. Chewing lice have a wider mouthpart that they use for feeding on dead or sloughing skin. Both types of lice can cause severe irritation and itching. This leads to restlessness and an animal that is focused on rubbing and scratching instead of on eating, leading to decreased performance and unthriftiness.
One University of Nebraska study1 indicated that moderate to heavy lice populations may reduce weight gains of calves by as much as 0.21 lb/day. It also indicated that calves fed at a higher nutrition level had lower lice populations and were affected less severely by lice than calves fed a maintenance ration.
Lice live on their host all the time. The typical life cycle starts with adult females laying eggs (nits) which are deposited and attached to hairs close to the skin. Hatching occurs in about eight days, and development through three nymph stages occurs over the next three weeks. The feeding habits of immature lice are the same as those of the adults. After reaching the adult stage, females are ready to lay eggs within a couple of days. They outnumber the males and live about six weeks. The life cycle from egg to egg is typically completed in about four weeks during cold weather.
Louse infestations typically begin to increase around November/December and peak out around January/February. While lice are most abundant on livestock during the winter when animals are under stress from cold weather and poor nutrition, the reproduction rate for lice slows dramatically in warm weather months. In the summer, only a few lice will persist in a herd by moving to areas on the animal that are protected from high temperatures and sunlight. Older cows or bulls are the most likely animals to carry lice through the summer months. Lice are spread by animal-to-animal contact. Nose-to-Nose contact by livestock sharing a common fence can be sufficient for spread of these insects. Typically, younger stock and old thin or debilitated cattle will be affected by the worst cases in a herd. Nursing calves can also be affected. A poor nutritional state along with a high stocking rate can lead to more severe outbreaks with the affected animals rubbing out patches of hair and damaging their skin.
A variety of options exists for control of lice. The most popular formulations tend to be pour-ons because of the ease of use. There are two main categories of pour-ons for lice control – insecticides and endectocides. Insecticides for lice control include permethrin, coumaphos, lambda-cyhalothrin and cyfluthrin (these include common products such as Brute, Durasect, Ultra-Boss, Co-Ral, Saber and Cylence). Pour-on endectocides include ivermectin, doramectin, moxidectin and eprinomectin (with common products including Ivomec, Dectomax, Cydectin and Eprinex). Pour-on endectocides typically cost more than insecticide pour-ons, but they also control internal parasites. Some of the endectocides are also available as injectable formulations; however, these are only effective against sucking lice. Dust bags, backrubbers and ear tags may be useful methods for lice control as well. Most insecticides are effective against adult lice and nymphs. However, few have activity against louse eggs, potentially allowing residual populations of lice to remain on animals for some time after treatment. This means that a follow-up treatment may be required. Always follow dosage and administration directions as well as any withdrawal times specified on the label. You may obtain the Extension publication MP144, Insecticide Recommendations for Arkansas, from your county Extension office for more treatment suggestions. Or, an electronic copy of the publication can be found here: http://www.uaex.edu/Other_Areas/publications/PDF/MP144/MP-144.asp.