Attention to detail is important when planning lice control

The vast majority of beef cow-calf producers in Western Canada will use a pour-on endectocide product for parasite control, usually at some point in autumn.

Most of those producers are mainly concerned about lice control. Using the pour-on product has become such a routine procedure that many of us don’t pay a lot of attention to the details.

It would appear that in the past few years, lice outbreaks have appeared to be slightly increasing in frequency. This may be due to several factors. Lice are very heat sensitive and prefer cold weather. We’ve had a couple of fairly cold winters in the past two years, which potentially makes lice more difficult to control.

Biting lice are not as easily controlled with avermectins and we may be potentially seeing more cases of biting lice rather than sucking lice. There could also potentially be a gradual build-up of some level of resistance to some of the avermectins that are commonly used to control lice. This is difficult to prove because there isn’t an easy test for resistance and so we don’t know how much this factor might be contributing.

Finally, we might be getting a little more careless about when and how we apply our parasite control products.

To ensure optimal lice control we need to pay attention to details:

  • Use the correct dosage and apply it correctly. Make sure you are applying the correct dosage in a long strip along the backline of the cow. Many producers underestimate the weight of their cattle and sometimes use an inadequate dosage. Readjust the dosage for larger cows and smaller heifers. It is also important to not apply these products when the cattle are wet or exposed to a lot of rain or snow. Like any veterinary pharmaceutical product, we need to read and follow the directions on the label.
  • Prevent reinfection of your herd. Absolutely all of the animals in your herd need to be treated with the pour-on product within a four-week period. If you leave just one or two animals untreated, they can be a source of lice that can then re-infect the rest of the herd later in the year. Don’t forget to treat your bulls as well.
  • Don’t re-introduce lice with additions to the herd. If you bring other animals into the herd after you have treated the main herd, they should be treated at least 10 to 14 days before introduction to make sure they don’t re-infect your cattle that have already been treated. This may mean that you have to effectively quarantine these new cattle until they can be introduced safely.
  • Treat the cattle at the correct time of year. Most outbreaks of lice infestations happen in cold weather, often in February and March. Lice are very sensitive to heat and prefer cold temperatures. In hot weather, they tend to hide on the underside of the cattle and are less likely to be killed when using pour-on products. If you treat the cattle too early in the year when temperatures are still warm, you will be very unlikely to get a good kill of the lice population. If your cattle come home from pasture in September, you should definitely wait until colder weather before applying the pour-on endectocide products.
  • If you do see itchy cattle, get a diagnosis before reapplying endectocides. Lice are easy to identify and can be seen if you inspect the hair around the head, sides of neck, dewlap, flanks and tail switch. Biting lice are very mobile and move quickly away when the hair is parted. They are light brown in colour and have a rounded head. They are often seen on the dorsal surface and the flanks of the animal. Sucking lice are usually fixed in place and are somewhat easier to find as a result. They are grey or blue-grey in colour and have pointed heads. They are more likely to be found in the head and shoulder area of the animal.

If we pay attention to all of these details when using the pour-on endectocide products, I believe lice outbreaks will become much less common. It is such an easy product to apply that it is easy to get careless and not follow all of the label directions. Ensuring you don’t treat too early in the year when temperatures are still warm and ensuring you don’t re-introduce lice through animal additions or by failing to treat certain animals will prevent many of the problems we see.

Your veterinarian can help with getting a definitive diagnosis of itchy cattle to rule out other causes such as mites or other causes of dermatitis. They can also help you to choose from a variety of products, such as permethrins and endectocides, that will work best for your operation to help control external parasites.

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