Lice control in cattle
Lice are small (1-3 millimeters long) wingless insects that feed on the blood and skin tissues of cattle. Three species of sucking lice and one species of biting or chewing lice commonly infest cattle in the United States. [Fig. 1]
They are spread in-herd through direct animalto-animal contact. They can become a problem in the fall and through the winter months.
Common symptoms of lice include loss of hair, excessive rubbing against fences, biting infested areas of skin, rough and patchy coat, and general unthrifty appearance.
Despite their small size, cattle lice can still be seen with the naked eye or with a magnifying lens after parting the hair of the infested animal. Lice eggs or nits attached to the hair [Fig. 2] are good indicators of an infestation. Cattle lice infestations usually start in the head, ears, topline, and brisket. Heavily infested cattle will have lice all over the body. Inspecting cattle for lice should start in the fall and continue through winter.
An average infestation level of three or more lice per square inch of skin is considered economically significant in beef cattle on a growing or finishing ration. Research from the University of Nebraska indicates that lice infestation levels of 10 or more lice per square inch of skin can reduce average daily weight gains by up to 0.12 pound per day (Campbell, 2006).
There are many effective endectocides formulated as pour-ons and injectables. Because biting lice do not directly feed on blood, they are less affected and may not be included in the label of the injectable formulations of some endectocides [see Table 1]. However, both biting and sucking lice can be effectively controlled by endectocides formulated as pour-ons.
In addition to endectocides, insecticides that kill lice on contact [see Table 2] are also available and effective against both sucking and biting cattle lice species. They can be applied as pour-ons, sprays, backrubber oils, and dusts.
Because lice infestations usually build up later in the season, fall treatments with endectocides for helminths and cattle grubs may not be enough to also satisfactorily control cattle lice. A separate treatment for lice is usually necessary in the winter.
Consult with your veterinarian when using endectocides or any systemic insecticides to discuss application timing in connection with cattle grubs (Hypoderma lineatum and Hypoderma bovis), which may or may not also be present in the host animal to be treated.