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Get ahead of lice with a plan to control the population

published: October 20th 2017
source: Zoetis


The winter of 2016-17 was a challenge for controlling lice in the beef cow herd. Varying weather conditions may have been the heart of the issue as it means a critical adjustment in parasiticide application timing.


“The weather the fall of 2016 was mild up through Thanksgiving, so lice didn’t really begin to replicate until early December,” said Jon Seeger, DVM, managing veterinarian with Zoetis. “Often, we tend to apply our external parasite control products in conjunction with other herd events like weaning or pregnancy-checking earlier in the fall. When the lice population exploded, we were past the duration of activity for many products.”


Dr. Seeger explains that lice are on cattle throughout the year, but populations tend to migrate to the lower parts of the body during the summer months seeking area out of the direct sunlight and heat. As weather turns colder, the hair coat gets longer and denser, and the days get shorter, lice move to the neck, shoulder and rump areas. When weather conditions are right, lice can replicate quickly.


“It is important to understand the life cycle of a louse to truly apply parasite control products at the right time,” Dr. Seeger said. “The adult louse lives about 14 days on the animal, laying eggs which are attached to the hair shaft. The eggs hatch about 14 days later.”


Dr. Seeger says this means that the parasite control product has to last long enough to not only kill the current lice population, but also the lice that will hatch from the current egg population as current parasiticides do not kill the eggs. 


Therefore, it’s important to read the label for duration of activity information. For example, Dectomax® (doramectin) Pour-On has 77 days of duration against the cattle biting louse (Bovicola bovis), and is the only pour-on with duration against long-nosed cattle louse (Linognathus vituli) at 42 days.


“By knowing how long the product is active in the animal’s system, it gives us a better idea of when to apply the product for the best control of lice,” Dr. Seeger said. “If the lice season extends beyond the duration of the active ingredient, it may be necessary to re-treat the herd. Work with your veterinarian to establish the best timing for optimum control with a proven effective product.” 


Dr. Seeger offers the following tips as you work with your veterinarian to improve your lice control efforts this fall and winter:

  • Treat every animal — don’t miss any. Lice spread easily.
  • Time application to control lice in concert with weather / temperature conditions as they vary from year to year. Apply product when the weather is colder and lice are replicating, not based on convenience to apply with other herd working events.
  • Apply the correct dose based on the weight of animal. For Dectomax Pour-On the dosage is 1 mL per 22 lbs. of body weight. This is critical for the product to be most effective.
  • Be conscientious with applying the product — apply down the middle of a clean, dry animal from shoulders to tailhead.


For more information about lice control and Dectomax Pour On, please visit with your veterinarian or Zoetis representative.


Dectomax Pour-On has a 45-day pre-slaughter withdrawal period. Do not use in female dairy cattle 20 months of age or older. Do not use in calves to be processed for veal. Dectomax has been developed specifically for cattle and swine. Use in dogs may result in fatalities.


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