Fecal Egg Counts may Help Combat Antiparasitic Resistance in Cattle

The Problem

When left untreated, intestinal nematodes, also known as worms, decrease cattle feed intake and cause intestinal tissue damage and blood loss. These effects reduce efficiency at every level of production, from reproduction and milk production to weight gain in the feedlot. The losses lead to increased costs to the producer and harm to the cattle’s wellbeing.

The Work

Eva Wray, a post-doctoral research associate for the Arkansas Agricultural Experiment Station, tested the effectiveness of different drug classes for treatments of worms using fecal egg counts. If the egg counts decreased, then the treatment was effective. If the egg count increased, the treatment was ineffective. When exposed to ineffective worm treatment, parasites sometimes reproduce faster through a process called “compensatory responsiveness.”

Wray worked with Jeremey Powell, veterinarian and professor of animal science, who administered worm treatments and collected samples.

The Results

Wray’s findings indicate that parasites infecting Arkansas cattle may be resistant to the macrocyclic lactone drug class, which includes ivermectin, cydectin and moxidectin. The overuse, misuse and lack of new products have led to extensive drug resistance in Arkansas.

The “white wormers,” named because of their white color, are still effective for treating parasites, and Wray hypothesizes it is because they are administered orally. Oral antiparasitic products for treating cattle are not popular as “pour-on” treatments because of how time consuming and difficult it is to round up cattle and administer the medicine. The macrocyclic lactone treatments are poured on cattle feed, which is easier to administer.

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The Value

Using the correct dewormer saves producers money, because they are not spending money on ineffective drugs and their animals are healthier and more productive. Successfully treating for worms can help farmers earn as much as $130 more per head of cattle, Wray said.

Using fecal egg counts to determine the treatment threshold also benefits producers because it guides them on knowing when an animal requires treatment. Taking the time to use an effective treatment can also extend the effectiveness of these drugs over time by slowing the development of resistance.

About the Researcher