Lice are lousy deal for cattle

Cooler weather brings weaning calves, politician promises, hunting season and increased incidence of lice predation in cattle. Left uncon­trolled, lice can cause problems in the herd. Protecting cattle from lice entails understanding the life cycle of lice, recognizing the potential damage and using effective methods of control.

In general, every herd has some level of lice infestation. Lice are carried from season to season by a small percentage of the herd that act as reservoir hosts. Clinical signs of lice-infected cattle generally begin with constant rubbing and scratch­ing within the herd. Fences, posts, water troughs, trees and any other stationary object could be subject to damage from this rubbing. As the in­fection and irritation continue, large hairless patches will become evident on animals.

Beyond clinical signs, further diagnosis requires seeing adult lice on the skin. Parting the hair will reveal the lice. They are very small— roughly the size of a grain of sand— but can still be seen. The economic threshold for treatment is roughly 10 lice per square inch.

Louse life cycles are generally three to four weeks and spent entire­ly on animals. First, female lice lay eggs, which are glued to the host’s hair. Nymphs hatch from the eggs one to two weeks later and become fully developed adults in about two weeks. Adult females can lay approximately 30 to 40 eggs during their life. If not controlled, a single adult female in September can result in approximately 1 million lice by January.

Two types of lice live on cattle: sucking lice and biting lice. Sucking lice feed on the host’s blood and are most often found along the top line of an animal’s back. However, they can spread to the poll and tail head. Biting lice, which ingest skin, hair and scabs, are more widespread on the body. In the U.S., cattle can be infested by one species of biting louse, Bovicola bovis, and four spe­cies of sucking lice: the long-nosed cattle louse (Linognathus vituli), the little blue cattle louse (Solenopotes capillatus), the short-nosed cattle louse (Haematopinus eurysternus), and the cattle tail louse (Haematopi­nus quadripertusus).

Lice infestation can result in lame­ness, allergic responses, restlessness, agitation and skin damage from ex­cessive rubbing or scratching. Open skin leaves cattle more inclined to illness and infections. If left uncon­trolled, lice can cause anemia, lower milk production, decreased feed efficiency and reduced weight gain. Cattle with lice will recover from disease stress slower than non-infest­ed cattle.

Both sucking and biting lice are equally harmful to cattle, and both respond to the same treatments. There are a variety of insecticides that can effectively control lice. Dusts, pour-on products and sprays provide easy-to-use and versatile treatment options. Traditional treat­ments involve a two-step process: First, treatment to kill adults and nymphs on the animal, followed by a second treatment three weeks later to kill adult lice and nymphs that hatched from eggs after the first treatment. Treated cattle should be re-examined about two weeks later.

One treatment option is avermec­tin endectocides. These products come in pour-on formulations and injectable formulations. Avermectins treat internal intestinal nematodes but also treat external parasites such as lice. It is important to note that the injectable formulations do not work on biting lice since they do not blood feed. Another option is a non-systemic topical treatment, typically pyrethroid products similar to what is used to control horn flies during the summer. These products are very effective against adult lice but do not affect the larvae or eggs. Retreatment is often needed 14 days after initial treatment.

Management practices should be undertaken to prevent re-infestation. Lice are spread primarily through animal-to-animal contact, includ­ing feeding, resting, breeding or shipping. Due to this threat, facilities used by infested cattle should either be treated with insecticide or remain empty for 10 days before allow­ing clean stock to enter. Any new animals should be isolated from the resident herd and treated before they are introduced to the herd.

Read the pesticide label and use only according to the directions. Know what personal protection equipment is required. Be sure that those making the application are trained in the proper use of each product and the appropriate equipment.

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