Growing Beef Newsletter
January 2026, Volume 16, Issue 7
'Tis the season for itchy cattle
Chris Clark, ISU Extension and Outreach beef specialist
For beef cattle producers in the Midwest, the hope of the new year is often accompanied by itchiness and hair loss in their cattle. Lice are common parasites of cattle that often show up in late winter because the pathogens tend to thrive in winter conditions.
Lice are tiny, wingless insects that are common external parasites of cattle. There are two general types of lice: sucking and chewing lice. Sucking lice feed on the blood of host animals while chewing lice tend to feed on skin cells, exudates, hair, and other organic material found on the surface of the skin. Lice are cold weather organisms and are most active in the winter months. They are spread by direct contact so closer quarters in winter feeding areas can play a role in direct transmission from animal to animal.
Common clinical signs include excessive rubbing, restlessness, hair loss, rough hair coat, skin irritation, and presence of lice and nits. It may be tempting to overlook lice infestation as merely a nuisance but, particularly with severe infestations, lice can cause performance issues and numerous secondary problems. By stealing nutrients and causing behavioral signs that may burn calories and interrupt normal feeding, lice have been shown to reduce weight gain by up to 0.21 pounds per day. Additionally, lice can reduce feed efficiency, hair loss can increase risk of cold stress, damaged skin can be at risk of secondary bacterial infections, and stress and anxiety can suppress the immune system increasing risk for illnesses like Bovine Respiratory Disease. Of course, sucking lice can potentially suck enough blood to cause anemia and can serve as vectors for systemic bloodborne diseases such as Anaplasmosis and Theileria.
To optimize treatment success, work with your veterinarian to choose the best product and follow label directions. There are numerous medications and formulations to pick from. One important consideration is whether to use systemic or topical medication. Systemic means that the medicine gets absorbed into the bloodstream and these medications can be injectable or pour-on. Care must be taken to not use systemic drugs during the winter in cattle that may have migrating grubs in the esophagus or spinal column. Killing these grubs can cause severe inflammatory reactions that can cause severe and potentially fatal conditions such as bloat and paralysis. Work with your veterinarian to determine your risk level and the appropriate timing for use of systemic endectocides in your geographic area. Topical medications may be safer options during the during the winter months because they are not absorbed systemically and should not kill migrating grubs. Rather, they kill lice or disrupt parasite life cycle through direct contact with the organisms on the skin.
Keep in mind that systemic drugs tend to be more effective to treat sucking lice while topical drugs tend to be more effective at treating chewing lice. Systemic drugs are not that effective against chewing lice because the organisms do not get readily exposed to the blood of the host. Topical medications though, will contact and kill both sucking on chewing lice on the skin of the animal. Therefore, if animals are infested by chewing lice, if producers do not know which type of lice their cattle have, or if there is concern about grubs during the winter, topical medications are the better choice.
Whatever medication is chosen, proper application is critical. Some drugs are effective with just one dose while others are labeled for reapplication two weeks after the first dose. All animals in the group should be treated as untreated animals can serve as reservoirs of parasites and sources of reinfestation for treated cattle. Apply the proper dose based on label directions and animal weight. Underdosing may allow some lice to survive while overdosing can be an issue in terms of side effects, withdrawal times, and things like that. Knowing animal weights and dosing accordingly is critical for efficacy and safety.
Follow label directions regarding placement of pour-on medications. Especially for topical pour-ons, adequate coverage is important for efficacy. Labels may describe dosing along the midline from poll to tailhead or perhaps applying part of the dose to the face or head. For best results, follow these application directions just as described on the drug label. Finally, to slow the development of resistance it can be helpful over time to rotate through different drugs with different modes of action. Again, your veterinarian can help you develop a drug rotation schedule that makes sense for your operation.
This time of year, most of us are looking forward to warmer weather, and with warmer weather, lice will become less active and ultimately go into dormancy over the summer. In the meantime, thoughtful management can help mitigate the problem and minimize performance loss and secondary issues.
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