The following article was written by Megan Van Emon, MSU Extension Beef Cattle Specialist. The complete article is available at: https://animalrangeextension.montana.edu/beef/moovingminutes.html

Be on the lookout for lice in 2021. As temperatures decrease, lice may become an issue on cows, bulls, and calves. Lice feed on blood (sucking lice) or skin and hair (chewing/biting lice). Lice infestations typically occur on beef cattle that are stressed from the cold weather, inadequate nutrition, internal parasite infestations, or lowered immune systems.

Heavy lice infestations can result in reduced feed efficiency, milk production, and weight gains. Additionally, lice infestations can lead to anemia, skin infections, and other diseases.

Adult lice are between 1/16 and 1/8 inches long and spend their entire life on the host. The louse life cycle is approximately 3-4 weeks. Lice are spread throughout the herd by direct contact. Therefore, treated cattle next to untreated cattle can lead to reinfection.

Several methods may be used to provide lice management including backrubbers, dust bags, pour-ons, and injectables. It is important to note that injectables are only labeled for control of sucking lice. Backrubbers and dust bags should have daily access to provide better control of the lice. Additionally, both backrubbers and dust bags should be checked weekly to determine if they need to be recharged with fresh insecticide. The most popular control method is pour-ons, which are applied down the mid-line of the back and the most popular control method. Care should be taken to ensure the proper dose is provided to each animal per label instructions.

Three insecticides commonly used for lice control are pyrethroids, avermectins, and spinosad. Pyrethroids commonly include piperonyl butoxide which increases the activity of the insecticide. Pour-ons that use

See Page 3: Green

pyrethroids are non-systemic, don’t kill louse eggs, and require two applications, 14 days apart. Avermectin pour-ons are systemic, typically cost more, and also control several internal parasites. Avermectin pour-ons also require withdrawal times prior to slaughter. Spinosad pour-ons are non-systemic and require two applications, 45-60 days apart.

Several methods and products are available for lice control in beef cattle. Make sure to read labels of the products to determine the species affected, dosage required, and withdrawal times. One key aspect of insecticide use for lice control is to alter the active ingredient each year. By alternating the active ingredient each year, you will reduce the chances of breeding resistance into the lice populations. I suggest using a 2 to 3 year rotation of active ingredients to help reduce resistance.

Montana State University, U.S. Department of Agriculture and Montana Counties Cooperating. MSU Extension is an equal opportunity/affirmative action provider of educational outreach.