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How do I evaluate a Fecal Egg Count Reduction Test (FECRT)?


Administration of an anthelmintic does not guarantee the animal has been dewormed.

A Fecal Egg Count Reduction Test (FECRT) can be used to assess anthelmintic efficacy by calculating the percentage of worms killed by the drug administered. To perform the test:

Conduct a FEC before deworming followed by a second FEC 7, 10, or 14 days post treatment (varies with drug). A reduction of less than 90-95% indicates resistance.

FECRT Test Analysis Table

Kaplan, 2004 performed FECRTs on 1274 horses at 44 large stables in Georgia, South Carolina, Florida, Kentucky, and Louisiana. Four different dewormers were evaluated on each farm: fenbendazole, oxibendazole, pyrantel pamoate and ivermectin.

The percent of farms found to harbor resistant worms were as follows: 97.7% for fenbendazole, 0%, for ivermectin, 53.5% for oxibendazole and 40.5% for pyrantel pamoate. In terms of actual reductions in fecal egg counts (FEC), the mean percent reductions for all farms were 24.8% for fenbendazole, 99.9% for ivermectin, 73.8% for oxibendazole and 78.6% for pyrantel pamoate. With the exception of ivermectin, these values are far below the levels needed for effective worm control.

The problem of anthelmintic resistance in small strongyles is worsening.

The prevalences of resistance to fenbendazole, oxibendazole, and pyrantel pamoate found in this study were far greater than in any previously published report. Furthermore, results from all 5 southern states were remarkably similar despite major differences in the types of farms and in physical geography. This suggests that drug resistance in small strongyles is highly prevalent throughout the entire southern United States and probably nationwide. These results indicate the following:

(1) that drug resistance in small strongyles is much more common than is commonly recognized
(2) that the problem of anthelmintic resistance in small strongyles is worsening
(3) anthelmintic resistance may be more severe in the United States than elsewhere in the world.

Egg Reappearance Period (ERP):
The ERP is the time interval between the last effective anthelmintic treatment and the reappearance of eggs due to re-infection.
……..Moxidectin: 10 – 12 wks
……..Ivermectin: 6 – 8 wks
……..Pyrantel pamoate: 4 – 5 wks
……..Fenbendazole: 4 – 5 wks
Avoid administering any dewormer more frequently than its ERP. Younger horses tend to have shorter ERP than older horses.

“I never felt right treating something I couldn’t see, and I always suspected my horses didn’t need to be wormed as often as recommended. Now I have my own FEC lab and Eggzamin has helped me learn to do the test and  identify parasites. I can test my horses to determine if they need treatment, and I am finding that they need it much less frequently!”   

~ Lee Posey, Oregon