Monday, February 21, 2011

Anthelmintic resistance

Anthelmintic (dewormer) resistance is a worldwide problem. It is when deworming fails to reduce fecal egg counts by 95 percent or more. Severe resistance exists when an anthelmintic fails to reduce fecal egg counts by more than 60 percent.

There are two ways to determine anthelmintic resistance: the fecal egg count reduction test (FECRT) and the DrenchRite® larval development assay (LDA).

With a fecal egg count reduction test, before and after fecal egg counts are compared for an anthelmintic treatment. It is suggested that both treated and untreated (control) animals be evaluated, so that the differences observed can be attributed to the anthelmintic and not something else. Producers can learn to do their own fecal egg counts. 

The DrenchRite® assay test is an in vitro test for drug resistance. It utilizes a pooled fecal sample from 10 or more animals. The test is available through the University of Georgia College of Veterinary Medicine. It is an "expensive" test but offers an alternative to the laborious task of performing fecal egg counts.

Anthelmintic resistance varies significantly by farm and region, but depends to a large extent on past anthelmintic use. If you have dewormed your animals frequently with certain drugs, you should expect some level of resistance. If you have injected anthelmintics or used pour-on products, this will have accelerated drug resistance.

Sheep and goat producers are encouraged to test for drug resistance, as the success of any effective parasite control program (e.g. FAMACHA©, Five Point Check©) depends upon the use of effective treatments.

DrenchRite® Larval Development Assay

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