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Innovations in Parasite Management

Goal of new long-acting dewormer is to break the parasite life cycle.

OVERLAND PARK, Kan. (Nov. 3, 2015) — Why deworm cattle? Well, duh! It’s to kill worms. Right?

That is correct, but according to Merial technical services veterinarian Tony Moravec, there is more to it. Moravec talked about innovative parasite management, and deworming pasture cattle in particular, during the 2015 National Angus Convention Nov. 3-5 in Overland Park, Kan.

Moravec said relieving cattle from the burden of parasitic worms helps the animals’ immune systems function better. Cattle are then more apt to receive optimum benefit from nutrition and other health management practices. Moravec said the goals of deworming are improvement of feed conversion, weight gain, milk production and fertility.

Moravec reviewed the life cycle of worms, explaining how cattle ingest worm larvae present on grazed pasture forage. Within the animal, worms mature, reproduce and their eggs pass from the animal in feces.

“Then, it starts all over again. There is potential for grazing cattle to become reinfected with every bite,” said Moravec. “The traditional approach to parasite management is to clean up the cow, but what if we could break the cycle?”

Noting how Merial’s Longrange® injectable dewormer remains active for an extended period, Moravec said treatment early in the grazing season can relieve animals of their parasite burdens and decrease the infectivity of pastures. Most conventional dewormers remain active for a few weeks, or only a few days, and animals have ample opportunity to become reinfected unless deworming is repeated multiple times during the grazing season.

A long-acting dewormer eliminates worm larvae ingested later, with less frequent handling, and fewer eggs are passed to contaminate pastures.

Addressing the issue of parasite resistance to dewormers, Moravec said there are two opportunities for resistance to develop, regardless of the kind of dewormer used. One opportunity, called head selection, can result at the time of treatment, when a complete kill is not achieved and some parasites survive to reproduce. Moravec said this most often occurs when animals are under-dosed.

Resistance due to tail selection occurs as the dewormer’s drug ingredient is exiting the animal’s body, dropping below therapeutic levels. Parasites exposed to sub-lethal drug levels survive and reproduce. With either head selection or tail selection for resistance, the result is a next generation that is hard to kill.

Moravec advised producers to administer dewormer at doses appropriate for individual animal weight, and not a pen average, to reduce head selection for resistance. Using a dewormer with a long contact kill time, and does not depend on slow release of a drug stored in fat tissues, will help remedy tail selection for parasite resistance.

According to Moravec, Longrange injectable parasiticide offers persistent activity for up to 150 days. Its extended duration of activity is provided by technology that allows a gradual release of eprinomectin within two peaks, after which the drug rapidly exits the animal’s body.

Editor’s Note: This article was written under contract or by staff of the Angus Journal, which maintains the copyright. To request permission to reprint, please contact Shauna Hermel at 816-383-5270.