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The building resistance against dewormers

Photo by Anna Hastert

Product resistance seems to be more apparent in the agriculture industry.

A veterinarian talks about resistance to dewormers and offers suggestions for cattle producers tackling parasites.

Merck Animal Health continues its 15+ years worth of research into parasites.

Technicians collect fecal samples, in an effort to better understand treatment efficiency. They collect samples pre-treatment and log egg count numbers, then collect samples post-treatment and again, log egg count numbers. Dr. Kevin Hill, DVM, Merck Animal Health says egg count numbers should be reduced significantly post-treatment.

However, data suggests the effects of current treatment methods are decreasing.

“We should have a 90-percent kill, or reduction in count. We’re finding out that we don’t,” Dr. Hill said. “Most of the products being used today – Those reductions are more in the neighborhood of 60- to 70-percent. So we’re not doing a good job of killing parasites these days.”

Dr. Hill says organisms naturally adapt to treatment methods.

“The key idea is that most of the wormers we’re using today are in the ivermectin class. We’ve been using them for 30 years, and they’ve been doing a wonderful job. All biological organisms, over time, find a way to adapt and become resistant. That’s what our database is telling us…we no longer have the high efficacy rates we use to have, so we have to look for solutions,” Dr. Hill said.

Dr. Hill says introducing new deworming molecules to the market takes time. United States cattle producers currently have two molecules to utilize in treating parasites.

“Fortunately, we already have one in place, called fenbendazole. The secret with fenbendazole, which would commonly be referred to as a white wormer, is it’s an entirely different chemical class than the ivermectin,” Dr. Hill said. “If we switch, it’s extremely effective. It’s best to combine the two classes, so we don’t develop resistance to fenbendazole. Use fenbendazole at the same time as ivermectin, and we virtually have a 100-percent kill.”

Dr. Hill encourages producers to talk to their local veterinarian about best treatment plans.

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