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July 2013
Do you know which dewormer(s) are effective on your farm?



by E. Nelson Escobar
Small Ruminant Specialist
University of Maryland Eastern Shore

It is a constant complaint among farmers, extension agents, and animal scientists the fact that anthelmintic (dewormer) resistance is an on-going and increasing problem around the world.

In Australia, 90% or more of sheep farms are reporting that the sheep drenches farmers traditionally used to manage worm burdens are no longer effective as expected. In southern Germany, worms (Trichostrongylus spp.) in a Dorper sheep flock were reported to be 100% resistant to ivermectin and albendazole, and partially resistant to levamisole. This is called “a triple anthelmintic resistance.”

How is anthelmintic resistance determined?
Anthelmintic resisistance can be determined by a fecal egg count reduction test (FECRT). A FECRT is a test that yields results which are unique to every farm and identifies which drenches (anthelmintics) are effective to manage the worm population present at the farm.

The identification of an effective anthelmintic must be part of the integrated parasite management (IPM) practices, because if the FAMACHA© score in a sheep or goat is more than 3, the treatment administered to the animal must be effective in order to comply with the IPM criteria: the right drench at the right time.

However, the majority of producers do not know which drenches are effective to treat the population of worms infecting the sheep or goats at their farms. By the way, an updated chart listing anthelmintics and recommended withdrawal times (for goats) is available on the web site of the American Consortium for Small Ruminant Parasite Control.


By doing a FECRT every 2 to 3 years the sheep/goat farmer will be using an efficacious drench at the right time. Dr. Steve

Hart has described the procedure to estimate the egg



count reduction after a treatment and it is available on the web site.

Basically, fecal egg counts (FEC) are done before drenching and 10 to 14 days after drenching. The fecal egg counts are compared to determine if there was a reduction in the FEC values. It is a quick measure of dewormer efficacy.

The DrenchRite Assay can also be used to identify worm species and effective treatments.

Do not delay . . . do a FECRT today!

Love, S. 2011. Factsheet: Drench resistance and sheep worm control. NSW Government, Industry and Investment.
Voigt, K., M. Scheuerle and D. Hamel. 2012. Triple anthelmintic resistance in Trichostrongylus spp. in a German sheep flock. Small Ruminant Research. 106:30-32.

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