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It’s Been a Lousy Year for Range Cattle – Got Lice?

by Wyoming Livestock Roundup

As we have gotten around the state for spring activities this year, one common topic has come up with at least 10 ranchers – lice on cattle. Across the central and southern parts of the state, ranchers have indicated that this spring has been one of the worst years for lice that they can remember. 

Lice problems

Not only do lice make a cow and calf look physically bad due to the loss of hair, lice will also reduce weight gains, reduce milk production, reduce feed efficiency, slow the animal’s ability to recover from other stresses like disease, cause anemia due to blood loss and generally cause an animal to be unthrifty. Infestations may also lead to death losses, as at least four Wyoming ranchers have indicated they lost heavy bred cows that ended up on their backs from trying to scratch themselves in ditches to relieve the irritation. 

When cows start dying from lice, treatment becomes very economical. 

Lice problems generally become apparent in the late winter and early spring.  This year, as folks were gathering cattle for branding, the infested animals were very noticeable. The reports of lice infestation have also come in from ranchers using a variety of different treatment options, both injectables and pour-ons, at single application in the fall or multiple, with application in the spring and fall, times of the year. 


To better understand lice infestations and reduce potential losses, it is critical that we understand how the lice problem is an interaction between the parasite’s biology, animal production, weather and rangeland plant nutrition. 

First, lice spend their entire life cycle on the animal host.  Female lice deposit up to one egg per day, and the life cycle is completed in three to four weeks.  Therefore, many lice generations can occur in a relatively short amount of time. Lice eggs can take up to two weeks to hatch, depending on species and environmental conditions. A parasite treatment with shorter residual activity than this will not kill those un-hatched lice.

Lice are transferred from infested animals to un-infested animals through direct contact.  This can include nose-to-nose contact through a fence, particularly during the winter. 

Secondly, lice problems can accelerate during cold weather conditions when animals are under stress.  This describes this past spring pretty accurately as we continued to have cold and wet weather through early May. 

Third, animals that are in lower than ideal body condition due to inadequate nutrition may be more susceptible or less resilient to infestations. 

Fourth, animals that are also under stress from internal parasites and have a suppressed immune system may have higher than average infestations.  Thus, an integrated approach to managing lice is needed because many factors contribute to infestations.

In Wyoming we have four species of lice.  Three of these are sucking species and include the longnosed louse, the shortnosed louse and the little blue louse.  The other species is a biting or chewing species called the cattle biting louse or Bovicola bovis and is one of the most common species in the state.

Sucking lice used to be very common, but it is thought that the use of injectable insecticides have generally taken care of those species. However, injectables are unlikely to control the cattle biting louse, and it appears that much of the outbreak this year is from that species. 


The most effective timing of treatment is in the fall before lice populations have built up.  Four types of insecticide applications are available and include insecticide dusts – such as permethrin products, Python Dust or Rabon; backrubber insecticides – such as permethrin products, CoRal, Ravap, Ectiban or Prolate; pour-ons – such as Ultra Boss, Ectiban, Clean up, Ivermectin, Cydectin, etc.; or injections – such as Ivomec, Dectomax, Cydectin or other ivermectin products. Injectable products are only effective for sucking lice. 

Treating now in late spring/early summer is likely too late of an intervention and is unlikely to be profitable. This is because lice cannot persist when the animal’s skin and haircoat temperatures rise much past 104 degrees Fahrenheit. Only a few individuals are able to survive the summer and likely persist in the folds of skin where it remains cooler.

The use of a fall chemical treatment should be effective but may not be a silver bullet. 

Integrated treatment strategies

To truly manage the root of the lice problem, several other strategies should be considered and integrated with chemical treatment. 

First, maintaining ideal body condition of cows, especially in the fall and going into winter can improve their ability to deal with any parasite, including lice.  This can be accomplished by paying attention to pasture and forage conditions, production cycles and alternative feed resources. 

Second, during particularly severe winters, pay very close attention to the nutritional demands of animals and consider ways to optimize the quality of forage resources that are available to maintain condition.  This period of time is very difficult on cows, especially those that are calving earlier in the year and are in the later gestational stage. 

Third, manage other parasites, including internal parasites, to minimize parasite stress and optimize the immune system. Treatments for internal parasites are typically applied in the spring. 

Fourth, consider that some individual cows are more resistant to parasites and some individual cows are more susceptible to parasites than others.  This resistance can be heritable and conveyed to offspring that may become your replacement cows or future bulls. 

Anecdotally, this has been observed for lice infestations this spring where ranchers confirmed that an individual cow that was highly infested with lice had a heifer daughter that had been retained and also was highly infested.  Observationally, both were more infested than the average cow in the herd.  While I was unable to find any research documenting heritability of lice resistance in cattle, I did find a study that documented lice resistance heritability in sheep. 

Therefore, using lice infestation as another criteria for culling individual cows and their offspring may be important if lice are the primary parasite an operation is dealing with and could be considered as a longer term strategy to managing this problem.

A good resource is a publication from our retired Livestock Parasitologist Prof. John “Jack” Lloyd, “Insect and Related Pests of Livestock in Wyoming” that can be found online at

For more information contact me at and check out my blog “Rangelands4u” at

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