Lice are a common winter problem in cattle, especially in cold climates. Heavy infestations can rob valuable nutrition when cattle need it most, decreasing gain and leaving cattle more susceptible to disease.
Here is more recent information on lice control in beef cattle:
Doug Colwell, a livestock parasitologist in Lethbridge, Alberta, says two types of lice infest cattle, chewing lice and sucking lice. Chewing lice are probably the most common, but large populations of sucking lice are probably the most damaging.
All lice cause severe irritation and itching, causing cattle to react by rubbing, licking or chewing on themselves. Infested animals are often restless, focusing on their discomfort rather than eating. And, the broken skin that can result is an avenue for secondary infection, says Ralph Williams, a Purdue University entomologist.
Spread by direct contact
Lice are spread by direct contact; calves pick up lice from their mothers or herdmates. Lice can infest cattle all year round, but their numbers are typically low in summer because most lice shed off in spring with winter hair, says Jack Campbell, a University of Nebraska professor emeritus and veterinary entomologist.
Cattle’s winter hair coat provides lice protection and an ideal environment for reproduction, he says. The life cycle is 20-30 days and the entire cycle takes place on the host, which makes lice an easier parasite to kill.
Adult females attach their eggs to hairs, which hatch in 5-14 days. When the nymphs emerge, they look similar to adults, but smaller, and go through three molts within a week. They advance to egg-laying adults in about 14 days.
Campbell explains that adult lice don’t live very long apart from the host; nor do the eggs attached to hairs survive long in cold weather.
By March, longer days, more intense sunlight and the increased temperature will begin to crash lice populations, Colwell adds. “The lethal limit for lice is around 104°; the back of an animal in full sunlight gets warmer than that,” he says, so they retreat to cooler places on the animal.
Treatment and control
Maintaining cattle on a high plane of nutrition is the first step in lice control. “You need to ensure they’re healthy going into winter and well fed,” Williams says. Healthy cattle in good body condition have more resistance to lice and rarely carry heavy loads, he adds.
Most ranchers treat for lice at fall weaning; in some regions, this treatment also gets the last of the horn flies, as well as grubs. Campbell says the ivermectin pour-on formulation is fairly effective against both chewing and biting lice, whereas the injectable formulation is not.
Lee Townsend, University of Kentucky Extension entomologist, explains that pyrethroid pour-on insecticides are effective against all types of lice, whereas the avermectins, moxidectin and eprinomectin (systemic products) mainly kill sucking lice.
“Fall treatment using a systemic product is very effective for sucking lice,” Williams says. “For chewing lice, there are several brands of pyrethroid-based pour-ons that spread over the body via skin oil.”
Spraying is an option, too, but doing so on cold days can stress the animal, he adds. When using a spray, it’s important to wet the entire animal with high pressure to ensure both the skin and hair are thoroughly soaked.
Some pour-ons are systemic and are absorbed into the body to kill sucking lice, grubs and internal parasites at the same time. Systemic products that control external parasites (lice, ticks) and internal parasites (worms) are called parasiticides. Systemic products (either pour-on or injectable) must be used before winter to avoid adverse reactions due to death of migrating grubs, Williams says.
“If you fall-treat for lice and they recur later in winter, you can repeat the same treatment used in the fall,” he explains. “But, if you didn’t use a systemic product, you shouldn’t use it later in winter if the herd has any history of cattle grubs,” he adds. Dying grubs can create swelling around the esophagus or spinal cord. A non-systemic pour-on product for lice at that time would be safer.