Lice on Cattle
Lice are potential wintertime pests of several livestock species, especially stressed animals. In some cases, severe direct economic losses in cattle production caused by biting or sucking lice may occur. Heavy louse infestations add to the stress of cold weather, shipping, poor nutrition and internal parasite load. Lice are generally most abundant on animals during the period of greatest winter stress and continue through early spring.
Lice are winter pests because, generally, they do not survive well in the summer because hot temperatures are lethal. However, one or two percent of animals may serve as chronically infested “reservoir” animals. A few lice on the reservoir animals survive on cooler areas of the body such as the ear tips. As temperatures cool, lice may move onto uninfested animals. Crowed conditions that often occur at winter feed troughs exasperate this spread.
Lice are small (1⁄10 to 1⁄8 inch), wingless, species-specific external parasites of livestock and poultry. In cattle, one species of biting lice, the cattle biting louse (Bovicola bovis) and three species of sucking lice; the shortnosed cattle louse (Haematopinus eurysternus), the long-nosed cattle louse (Linognathus vitula), cattle tail louse (Haematopinus quadriptusus) and the little blue cattle louse (Solenoptes capillatus) occur. Sucking lice pierce the skin and suck blood while the biting lice move about on the animal chewing hairs, skin and secretions. Both types of lice are problems during the winter and early spring but as mentioned earlier reproduce year-round at least on some animals. Lice are spread from animal to animal by direct contact such as shipping or feeding. Animals infested with lice will have an unkempt coat, scaly skin and possibly raw areas on the skin. Infested animals will scratch and rub to relieve the itching caused by lice. Often in heavy infestations, clumps of hair will fall off. Weight loss or reduced weight gain can occur with heavy louse infestations.
Lice can produce multiple generations per year, thus allowing numbers to become high if uncontrolled. All louse stages (egg, nymph and adult) are found on the animal. Adult female lice glue eggs (called nits) to hairs, eggs hatch into nymphs in about 10 to 15 days, and after three molts, nymphs become adults. It requires about 1 month for an egg to develop into an adult. In cattle, light louse infestations are easily overlooked. Heavier infestations are easier to recognize by animals’ rubbing and loss of hair. A louse population on cattle can be estimated by examining five one inch square areas on the face, face, dewlap, neck, back and base of the tail. Lice populations on cattle are usually categorized as very slight (less than 5 per square inch), slight (5-10 per square inch), moderate (10-20 per square inch), severe (20-50 per square inch) and very severe (over 50 per square inch).
Good nutrition usually reduces the negative effects of lice infestations on livestock and is the foundation of a louse control program. Sufficient nutrition will allow the animal to better deal with blood loss and irritation. Another very important component of lice prevention is to assume that all purchased or “new” animals are infested. With this said, new animals should be isolated from the rest of the herd until a full course of louse treatment is completed.
Insecticides used for louse control are divided into two major categories; systemic products and nonsystemic products for winter treatment of lice on cattle, selection of the right insecticide is crucial. If cattle were treated with systemic products (endectocide) containing doramectin, ivermectin or moxidectin at the appropriate time for cattle grubs, then endectocides can be used to control lice in the winter. Pour-on endectocides will kill both biting and chewing lice while injectable insecticides kill only sucking lice.
However, if cattle were not treated with a systemic insecticide for cattle grubs at the appropriate time, then non-systemic products should be used. Non-systemic insecticides effective against lice include the pyrethoids such as permethrin, cyfluthrin, zeta-cypermethrin, gamma-cyhalothrin, and lambdacyhalothrin. Pour-on pyrethroids effective against lice include those containing permethrin, permethrin and diflubenzuron (an insect growth regulator), cyfluthrin, lambda- cyhalothrin and gammacyhalothrin. In addition, dust bags containing pyrethroids have shown efficacy against lice. Although organophosphate products containing coumaphos, famphur, fenthion, phosmet and trichlorfon kill lice, they can exhibit systemic activity in treated animals. Remember to follow label directions and that not all insecticides labeled for use on beef cattle are registered for use on dairy cattle. To see a listing of insecticides available for louse control, consult the animal section of MP144, Insecticide Recommendations for Arkansas. http://www.uaex.edu/publications/mp-144.aspx
