Check Cattle for Lice in Late Winter/Early Spring
By : Rory Lewandowski, Extension Educator Wayne County
Check beef and dairy cattle for lice infestations during the late winter and early spring months. Although lice can be present throughout the entire year, high numbers of lice are most likely during winter months when cattle have longer, thicker hair coats, which make self-grooming less effective in reducing lice numbers. Hot summer temperatures, and for pasture-based production systems, direct exposure to sun, plus rain showers, all play a role in reducing lice numbers and offer further explanation of why heavy lice infestations are most often seen during winter months.
There are two type of lice that may infect cattle: sucking lice and biting lice. It is possible to have both types of lice on any one animal. Sucking lice are blood feeders while biting lice feed by scraping cells from the surface of the skin and the base of hairs. Eggs, commonly called nits, are laid and glued as single eggs to hairs. Although there is some variance between lice species, in general, eggs hatch in approximately two weeks into an immature life stage called a nymph. Nymphs resemble adults except that they are smaller. They go through three molts, shedding their skin each time until they reach full adult size in about three weeks. Within a few days of adulthood, females begin egg laying and generally lay one egg per day. Adults typically live two to three weeks. Both sucking and biting lice spend their entire life cycle on the host. Sucking lice will die within a few hours off the host while biting lice may survive for several days if not exposed to direct sunlight. There is no alternative host for either type of lice. Lice are species specific. Cattle lice need cattle as hosts.
It is possible for lice to reach population levels of thousands or even tens of thousands on infected cattle. These types of infestations are associated with reduced weight gains, anemia, predisposition to other disease/illness as a result of accumulated stress and depressed immune response and/or slow recovery from an illness/disease. The economic impact of cattle lice is variable and not always well correlated with the severity of the infestation. However, a figure of ten or more lice per square inch is observed in most instances with a detrimental economic impact. One factor that can reduce the negative effect of lice is a high energy diet. Conversely, a diet low in energy can exacerbate the negative effects of a heavy lice infestation. This certainly should wave a caution flag for many cattle operations since there was a lot of high fiber, low protein and low energy hay made last year that is currently being fed.
Symptoms of a heavy lice infestation are readily visible. Cattle rub and scrape themselves to relieve the itching caused by lice. Clumps of hair will fall out, leaving bare and raw spots on animals. Other areas of the hair coat may exhibit a matted appearance. Cattle with especially heavy infestations of sucking lice are sometimes described as looking “greasy”. This is due to the cattle rubbing that crush the lice, resulting in a mixture of crushed lice, lice feces, blood and serum from the sucking wounds deposited on the skin of the infected animal.
Lice are effectively controlled with a systemic pour-on treatment of any of the ivermectin class of pesticides that include doramectin, eprinomectin, ivomectin or moxidectin. All of these products provide long-term control with a single application. These products are safe to use for a winter louse control application if cattle have previously been treated for grubs before November 1st. If cattle have not been treated for grubs, use of these systemic products may result in an adverse reaction if cattle grubs are at a critical stage in their migration, which may find them accumulated around the esophagus and/or spine of the animal. If grubs are killed when they are at these sites an inflammatory reaction can occur resulting in severe bloat or paralysis of the rear legs of the animal. Generally, the critical period is between November 1 and early January here in Ohio, and after that it is safe to use systemic products for louse control again. However, a February 7, 2001 OSU Extension Beef Cattle Letter article on grub and lice control written by former OSU Extension Veterinarian for Beef/Sheep, Dr. William Shulaw, contains the statement: “Treatment of cattle with grub larvae late in the winter or in early spring may kill the grubs without much danger to the animal, but the larval activity, or reaction to their death, can still cause muscle and subcutaneous tissue damage visible at slaughter.” Therefore, another alternative to treat late winter/early spring lice outbreaks in herds that have not been treated for grubs is to use non-systemic insecticides that contain active ingredients such as lambda-cyhalothrin, cyfluthrin or permethrin. Pour-on formulations are most effective.