Hair loss, lick marks and an unthrifty appearance are among the signs of a lice infestation. (Photo by Dr. Larry Hawkins)

As fall temperatures give way to winter, cattle lice numbers will increase.

Cattle lice are insects that thrive in cold conditions. Populations are most noticeable during December, January and February, and they decline during March when temperatures warm.

Lice are transmitted via animal-to-animal contact. Cattle with hair loss, an unthrifty appearance and leaving hair on fences and other objects from rubbing may be a sign of lice infestation.

Other factors, however, can mimic lice infestations, such as natural shedding, poor nutrition, mite infestations, mineral deficiency, photosensitivity and other diseases.

To determine if lice are the problem, secure the suspect animal(s) in a chute and perform a two-handed hair parting on the top line, withers and face.

Lice numbers of up to five per square inch represent a low population, six to 10 represent a moderate population, while more than 10 are considered a heavy population.

Studies indicate that heavy lice populations may reduce weight gains by as much as 0.21 lb. per day. These studies also show that calves fed at a higher nutrition level had lower lice populations and were affected less severely by lice than calves fed a maintenance ration.

Cattle louse treatment products fall into several categories: animal sprays, non-systemic (contact) pour-ons and endectocides (systemic pour-ons, absorbed internally and systemic injectable).

Some non-systemic pour-ons require just one application, and some require two applications spaced two to three weeks apart.

Systemic injectables work better on the three species of sucking lice than on the little red chewing louse.

A systemic pour-on effectively kills both chewing and sucking lice. Use of systemic control products between Nov. 1 and Feb. 1 is not advised as they may cause a host-parasite reaction from killing developing cattle grubs while they are in the esophagus or spinal canal of the animal.

If you are using these products, check with your veterinarian to be sure the timing of application is correct for your region of the country.

A systemic product used during fall weaning will not be a problem. Producers who did not use a systemic during fall weaning should consider using only non-systemic control products during this November to February time frame.

Successful louse control depends on application timing. Many livestock producers will administer an endectocide treatment at weaning time, usually late September or October, with intentions of controlling internal parasites, cattle grubs and cattle lice.

Producers who use this management strategy should monitor their cattle for signs of lice especially from December through February. This is necessary because while fall applications may help reduce lice populations, they may not remove the infestation.

If replacement animals are brought into a herd during the winter months, they should be examined for lice. If present, the animals should be isolated and treated before introduction into the existing herd.

When applying any insecticide control products, please read and follow label instructions.

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(Photo by Dr. Larry Hawkins)