Understanding Lice Infestation in Cattle

Lice Infestation in Cattle

Lice Infestation in Cattle

Lice are a common winter problem and heavy infestations with these small, flat-bodied insects can lead to economic losses due to reduced weight gains and general “unthriftiness” of infested cattle. In calves, moderate-to-heavy lice infestation has led to a 0.21 pounds/day reduced weight gain, according to a University of Nebraska-Lincoln study.

In general, lice populations are low in the summer months due to the effect of direct sunlight and  shorter hair coats. Additionally, self-grooming and rain keep the lice population in low numbers.

Understanding the life cycle and the detection of these parasites is important so that accurate prevention and control can be initiated with the goal of the smallest financial investment coupled with the most effective treatment.  

What types of lice affect my cattle?
Five species of lice are found on cattle in North America. Four are sucking lice:  short-nosed cattle lice, long-nosed cattle lice, little blue lice, and cattle tail lice. The fifth species is the biting lice. The sucking lice take a blood meal by inserting their mouthparts into a cattle vessel. The biting lice scrape bits of cattle skin, and eat that material. 

What is the life cycle of lice?
Lice have legs that can grasp onto hair very well, and they produce eggs, called nits, that are glued to hairs of cattle. After approximately two weeks, an immature form of lice, the nymphs, hatch out of the eggs. The nymphs resemble the adult form, and have the same sucking and chewing habits, but, unlike the adult lice, are unable to produce eggs. During colder weather, the life cycle from egg to nymph to adult louse takes three to four weeks. Lice are host specific and spend their entire lives on the host animal. Lice are unable to survive off the host for very long.  

How do I know my cattle have lice?
The sucking lice cause irritation of the skin, which leads to itchiness. Therefore, one of the first signs you can observe is that cattle that have lice will be scratching and rubbing themselves against trees, fences, feed bunks or other objects. This rubbing behavior will consequently lead to damage of the hair coat and hide. The hair coat will look dry and scaly, and hairless areas on the body will be seen. Two of the five species of lice are only found on the face and tail of cattle. Sucking lice may be found on the head, neck, withers, base of the tail, brisket, and along the inner surfaces of the legs.

Biting lice also cause itching and distress due to the movement and feeding habits of this parasite. Moderate infestations of biting lice in beef cattle typically lead to lesions on the withers, upper parts of the ribs and shoulders, and along the back.

When large numbers of lice are present — and other factors such malnutrition, cold stress, shipping and concurrent infection with internal parasites exist — the whole body can become affected, leading to weight loss, ill thrift and a compromised immune defense mechanism. In some cases (with a very high number of sucking lice), anemia, abortion or even death of animals can occur due to severe blood loss. 

Even if cattle do not seem to be infested with lice, it is advised to inspect for lice before purchasing or when they are handled for common procedures such as vaccinations or branding. Simply spread the cattle hair with your fingers to see if lice or eggs are present.  It is recommended to evaluate multiple areas on the body such as face, neck, brisket, back and tail head.

In severe lice infestations, sucking lice might be densely packed, creating characteristic quarter-sized black or blue spots. Biting lice do not like to be crowded and are usually not found in tight clusters. More than three lice per square inch indicate a need for treatment. 

How do my cattle become infested with lice?
Lice are transmitted from one animal to another by contact.

Up to one or two percent of the cattle in a herd can carry a high load of lice, even in the summer when high temperatures reduce the number of lice. These carrier animals are the source of re-infestation during the fall. Usually, the carriers are a bull or a cow in poor body condition. Offspring of carrier cows are also heavily infested. As such, beef cows should be treated before calving, and carrier cows should potentially be removed from the herd.

How can I control cattle lice populations in my herd?
Factors promoting lice infestations are crowding, reduced light intensity, malnutrition, weather and decreased immune system response. Therefore, it is important to maintain good cattle health through a high plane of nutrition, adequate body conditions, appropriate mineral supplementation and vaccination protocols. Cattle in good health are more resistant to lice infestation and will have lower lice numbers.

Newly-acquired livestock should be examined for lice, and, if necessary, isolated and treated before introducing them to the herd.

Control measures should be initiated before lice numbers on the cattle become high. Cattle should be inspected in the late fall for lice, and treatment should done before lice numbers are high and economic losses occur.

How do I treat my cattle against lice?
The control of this parasite is easy, and, generally, treatment is initiated in the fall to prevent a lice build up in the winter months.

Treatment with most of the available insecticides is effective against nymphs and adult lice. Lice eggs are not affected by most insecticides. Therefore, treatments at two-week intervals enable the stockman to kill any lice that have hatched since the preceding treatment. Many different insecticides and application methods are available for cattle lice treatment, such as sprays, pour-ons, or injectable products. The most popular application method is a pour-on due to its ease of application. Pour-ons are effective against sucking and biting lice on beef cattle. Injectable avermectins (e.g. ivermectin) are only effective against the sucking lice. 

Remember that your treatment success will depend on the proper dosing of all animals in the herd. Under-dosing or non-treatment of animals will lead to that herd being easily re-infected. Also, remember that “days until slaughter” will vary depending on the drug used. Therefore, it is always advised to check the drug label before applying.  

Can I use self-application devices such as dust bags or oilers for my cattle?
Self-application devices are handy, but they apply only a little or none of the insecticide to the brisket, abdomen or legs. Therefore, they will provide some lice control, but the best results are obtained when these self-application devices are used to prevent a serious build-up of lice populations. Insecticide-impregnated ear tags used for fly control have been ineffective in controlling lice.

What other things should I consider when treating lice?
Read the label on the pesticide used, especially when considering treatment of the same animal with a different pesticide in the near future. Toxic reactions may occur in cattle as a result of multiple applications of pesticides if administered too closely together or as a result of a combined effect of the drugs.

If medications for grubs are used for lice control after the “safe cut-off date,” there is a high risk of choking, bloat or paralysis as a result of an immune response to the cattle grubs dying in the tissues of the animal. Use grubicides for lice control only before the “safe cut-off date” or on cattle that have been already cleared of grubs.

 For specific recommendations on insecticides and treatment timing for lice control in your herd, please contact your local veterinarian.

*This article may not be reproduced without the written consent of the UC Davis School of Veterinary Medicine.

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