Most beef farmers are familiar with lice outbreaks on their cattle during the winter. It is a common fact that lice populations on cattle peak during the winter months. However, lice can still pose problems in the spring.

Lice are small, flat-bodied insects with legs modified for grasping hair. They depend on cattle to survive and can only live separate from an animal for a few days. There are two common species of lice that infest cattle: sucking lice and biting lice. Sucking lice suck blood from the host, while biting lice eat dander.

Female lice lay eggs at the base of the cattle’s hair. The eggs are glued individually to hairs and hatch in about two weeks. When the eggs hatch, the baby lice, called nymphs, emerge. The nymphs resemble the adults but are smaller. It takes the nymphs about three weeks to mature into adult lice. Adult lice live for two to three weeks, and the females lay about one egg per day.

Signs of infestation

The telltale signs that your cattle are suffering from a lice infestation are hair loss, raw spots, reduced weight gain and a general lack of thriftiness. While hair loss is not a big deal in the summer months, losing hair in the winter months can result in frostbite. USDA has estimated that livestock producers lose up to $125 million per year due to effects of lice infestations. This number includes both direct performance losses and wear and tear to facilities from cattle scratching themselves.

Cattle lose growth and production due to lice when they are itchy and distracted from eating. Their health is impacted from the inflammatory skin damage caused by both types of lice and blood loss from feeding by sucking lice. Therefore, determining the severity of the infestation is one of the most important things you can do.

To determine the severity of infection to an animal’s health, count and record the number and species of lice that are found per square inch of hide. A quick method to identify species of lice involves noting their reaction to being disturbed when the hair is parted. Sucking lice tend to stay stationary when disturbed and cluster together. Biting lice move when disturbed and do not like to be by other lice, so you will see individuals jumping around.

If the infestation is fewer than 10 lice per square inch, you can consider not treating. The economic threshold to treat is 10 or more lice per square inch of hide.

To treat or not to treat

If you decide to treat, it is important to select a product that will work for the population of lice you have present. Sucking lice feed on blood, so they are controlled more effectively with a systemic injectable product. Biting lice, however, feed on dander, so a systemic product has little effect on them. Biting lice are more effectively controlled with a topical treatment.

It is important to make sure you apply the product as directed by the product label to avoid future resistance issues, and follow all drug withdrawals.

You should also check the animals several weeks after treatment to make sure the treatment was effective. You may decide not to treat because lice numbers are low or the animals do not seem bothered by the lice infestation, but continue to routinely inspect the cattle to determine if their condition changes and treatment is warranted.

Keep in mind that lice populations will begin to decrease in activity as the weather begins to warm. Read more about dealing with lice in this article.

Schlesser is the Extension dairy agent in Marathon County, Wis. This column is provided by the University of Wisconsin-Extension’s Wisconsin Beef Information Center.