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Late fall better for lice and parasite control in cattle

Animal Health with Roy Lewis: A two-pronged approach to deal with internal and external pests

This diagram put together by Doug Colwell a research scientist at the Lethbridge Research Centre, shows the zones on an animal were lice are most likely to concentrate and be visible. Colwell is internationally recognized for his studies on the interactions between insect parasites and their animal hosts.

There has been lots of talk and questions from producers and large-animal veterinarians regarding the strategy needed for more effective lice and internal parasite control.

I the last couple of years there has been a large increase in the incidence of lice in Western Canada. Producers are searching to find ways to control lice that don’t involve running cattle through the chute any more than necessary.

We know lice prefer the cooler temperatures of fall and winter to multiply and therefore become more evident on common body locations. We also know how quickly lice can transfer to calves in the spring and cause irritation and blood loss.

Proper timing of treatment will hopefully improve product effectiveness. Unfortunately, we have gotten away from the very late fall and winter treatments mostly because it was more convenient to apply products during warmer temperatures

However, research is showing that moving from late-summer or early-fall treatment to late fall should improve product effectiveness. This would apply to feedlot cattle as well. It may mean that summer-placed cattle will need to be lice-treated at first implant, for example.

Along with timing, alternative products such as the category-three insecticides with names such as Boss, Saber, De-Lice or Cylence can be used effectively. Again, timing is critical for these pour-on products with slight differences in formulation. Basically, they are lower-volume pour-ons and are not systemic. They have no effect on internal worms. They are only effective for external parasites such as lice, although some are effective on ticks and mange as well. Ticks and mange mites are rarer. Follow your veterinarian’s recommendations if these parasites are encountered.

Some people are combining the late-fall treatment of the ivermectin products together with an internal dewormer and then following up with the insecticide pour-ons later in the winter if they see any clinical signs developing or as a routine to get a good treatment into them prior to calving.

Two applications

The other alternative is to go with two applications of the category-three insecticides to get the eggs later when they hatch. Either way should work fine but they do most likely involve another treatment through the alleyway to apply products properly.

Plan to treat the whole herd as a unit at the right time so you’re not leaving any group untreated as a source of contamination and spread to the others. New introductions or purchases should be treated upon entry into the herd.

Other options include using cattle oilers with approved products such as ectiban while others have a pymethrin base. Use either canola or mineral oil to carry the pest-control product. Even the rub brushes used by cattle in pens can be effective to physically remove the lice.

We will find this two-pronged approach to lice control will probably continue to be necessary. Keep in mind the need to follow the label recommendations. Unlike antibiotics, prescriptions cannot be written by veterinarians for species not included on the product label. This makes if difficult to find treatments for species like goats or bison that are not included on most insecticide labels.

We have gone a long time without much need to deal with lice, but now need to address timing, alternating products and examining to see which lice are causing us problems in order to better determine the optimal treatment strategy.

About the author


Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.



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