Livestock News

Timing and application critical in getting ahead of cattle lice


Many winters can be a challenge for controlling lice in the beef cow herd, and varying weather conditions may be the heart of the issue.

“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,” said Jon Seeger, DVM, managing veterinarian with Zoetis. “When the lice population exploded [like it did in one recent season], we were past the duration of activity for many products.”

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, they can replicate quickly.

“It is important to understand the life cycle of a louse to truly apply parasite control products at the right time,” 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.”

Seeger says this means that the parasite control product has to last long enough to not only kill the current 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,” 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.”

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.
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