Fall is the time of year we think about lice control, but is that the correct timing? More and more we hear producers and veterinarians lament about lack of effectiveness of lice control. Are lice getting harder to treat? Here’s a little history:

Cattle can have two types of lice: chewing lice (also called biting lice) and sucking lice. They live their entire life cycle on the animal. Yes, some lice can fall off the animal and live in bedding for a few days, but that is of minor significance when we think about controlling the parasite. The lice that you see causing excessive scratching and hair loss around the neck and shoulders during the winter are actually on the animal the entire year. Lice are at a much lower population during the warmer months of the year and they seem to infect some animals much easier than others. When the weather turns cooler and the cow’s hair grows longer, a louse population explosion ensues. One way cattle limit the lice population during warm weather is by licking themselves and others. A rough cow tongue applied to a slick, summer haircoat is quite efficient in eliminating some annoying lice. In winter, the cow’s long and thick haircoat protects the pest from the cattle grooming practice.

If you deworm your cattle with an injectable ivermectin-type product (Ivomec, Dectomax, Cydectin) you should also pour your cattle with a lice-control product. These injectable products are very good at controlling the sucking lice, but lack effectiveness against the chewing lice. Any newly purchased animals should be poured for lice and quarantined from the herd for 30 days.

Many veterinarians recommend a lice control product that contains an insect growth regulator (IGR) so that the cattle have lice control throughout the winter with only one application. Examples of products with an IGR are Clean-up II and Prozap Protectus. These products kill the adult lice and the nits (eggs) before they hatch. Most other products only kill the adults and require two treatments.

The application process is critical to obtain excellent results for controlling lice. If you use a product that is dosed at 3ml/100# with a maximum of 30ml/adult cow, the following application method is ideal:

1. For animals 1000# and over, set the dial to 13 ml and start at the poll and depress the trigger on the gun as you move the gun toward the middle of the back. Getting past the shoulders is the key.

2. Now do the same starting at the tailhead and go to the middle of the back. If there is a 6-10-inch area at the middle of the back without product, that is not an issue.

3. Set the dial to 4ml (or if you have a large herd, have a separate jug and gun) and put 4ml on the face. Some lice live under the chin, and this will help to kill these.

4. When applying the product, use the tip that is a single hole (not the shower tip) and press the tip down to the hide. The product must contact the hide to work.

Spraying a lice control product on the side of a cow as she walks or runs past is not going to give you the results you desire.

Timing of lice control is also critical. If you are walking cows through the chute well ahead of winter, this is too early to use a lice control product. Wait until cows start to develop a winter coat to treat them. Our rule of thumb for Central Indiana is to pour cows between Thanksgiving and Christmas. You want to wait until the louse population explosion occurs so that the insecticide will be the most effective. In some instances, this later time will correspond to when you give a pre-calving vaccination to the cows to help prevent calf scours and/or an inactivated IBR-BVD vaccination to improve colostral immunity of these pathogens.

Are lice developing resistance to some of the products? While we do not know for sure, it is a possibility. Nonetheless, utilizing the best product, pouring as outlined above and waiting to treat until the start of winter are all things you can do to decrease your chance of an outbreak.

If you have any questions about lice control, please contact your herd health veterinarian.