Cassandra Olds, extension livestock entomologist
Although most healthy cattle can manage lice burdens without intervention, some animals will develop heavy burdens which may require insecticide intervention. Lice populations are most active from December through to March with numbers naturally declining as we move into the warmer summer months.
Lice can be divided into two broad groups based on their feeding biology. Biting lice (also called chewing lice) feed on hair, skin and/or skin secretions. This feeding activity causes irritation and animals can often be seen scratching and rubbing which can cause significant damage to facilities and fences. Noticeable patchy hair loss may occur in animals with high lice burdens which will increase animal stress as they battle to insulate, leaving them susceptible to frostbite. Sucking lice are blood feeders with specialized mouthparts which tap directly into blood vessels similarly to mosquitoes. Severe infestations can result in anemia and production losses, especially in calves. Infestations of sucking lice can also cause rubbing, scratching and increased self-licking. In addition to production losses, lice feeding also results in hide damage, reducing leather quality. Long haired animal breeds with dense thick coats provide extra insulation and protection for lice and these breeds can be especially prone to infestations (Figure 1).
Identifying which lice type you have can be important as it may direct your insecticide choice. As a general rule, biting lice have large, dome shaped heads while sucking lice have more narrow, tapered heads (Figure 2). Only one species of biting lice impacts cattle (cattle biting louse, Bovicola bovis, Figure 1), with females being able to reproduce without mating. This is the most predominant lice species impacting cattle and is commonly found on adult animals especially along the back line of the animal and around the wither area. Four species of sucking lice impact cattle in the US, three of which are not common on the Great Plains region [little blue cattle louse (Solenopotes capillatus), shortnosed cattle louse (Haematopinus eurysternusis), cattle tail louse (Haematopinus quadripertusus)]. The fourth species of sucking lice, [longnosed cattle louse (Linognathus vituli, Figure 3)] can transmit Theileria orientalis, infection causing the disease theileriosis which can cause significant mortality, milk reduction and reduction in calf gains. This species can reach high numbers on calves but is found infrequently on adults. Special attention should be paid to the dewlap, neck and shoulders, as this is a preferred feeding site. By maintaining vigilant management and biosecurity, producers can protect their herds and flocks from lice, ensuring healthier and more productive livestock year-round.
Lice are host specific, meaning that the cattle lice are not shared with sheep, pigs or horses and visa-versa, but multiple species of lice can infest the same animal. As wingless insects, lice require direct body contact to move from animal to animal. Inspect new animals entering the herd to avoid lice introductions. Economic threshold for lice infestations is ten lice per square inch. To do this, part the hair of the animal and if more than ten lice are found per square inch, animals should be treated. Good lighting can help as lice are often light in contrast to the darker fur. If treating individual animals, keep treated animals separate until the treatment course has been completed to ensure they don’t transfer lice to untreated individuals. Tough egg casings protect the developing lice (also called nits) from insecticides, requiring that treatment be given twice, usually two to three weeks apart. This will kill any nymph lice emerging from the eggs before they are able to reach sexual maturity and lay eggs.
Several pyrethroid based pour-ons are available which effectively control both sucking and chewing lice. Those that also contain diflubenzuron, an insect growth regulator, need only be applied once as it targets the egg stage as well as emerged lice. Macrocyclic lactone products (moxidectin, ivermectin, eprinomectin etc.) are available as both pour-ons and injectables and provide extra coverage for nematodes. While a pour-on will target both sucking and chewing lice, injectables will only control sucking lice since biting lice do not feed on blood. Spinosad pour-ons offer a third chemical class for rotation, but similar to pyrethroids will require a second application to be effective. Although organophosphate chemicals will effectively kill lice, these are mainly available as spray or dust applications which may not be as practical to use in winter. If using duster or self-application oiler, put it in a place which animals will frequent often.
Do not use the same chemical group year after year, instead use a single chemical group for a year (pyrethroid, spinosad or macrocyclic lactone) before moving onto the next chemical group the following year. This rotation will allow you to not use the same chemical group more than once every three years, slowing the rate of insecticide resistance. Always check withdrawal periods and apply insecticides according to the manufacturer’s label. A list of chemicals and product names can be found by searching this database.
