Horse Illustrated Magazine

Rotating Classes

All dewormers are not alike. Each dewormer has an active ingredient (chemical) to control parasites in your horse. These chemicals fall into one of three different “classes,” and each controls different parasite species. When rotating dewormers, you need to rotate classes, not just the brand name or the chemicals within each class, otherwise certain parasite species may continue to flourish in your horse despite your best efforts.

Below is a chart of the three classes and the chemicals in each. For information on the various parasites each chemical controls, talk to your veterinarian and refer to dewormer product labels. Because they are considered drugs, equine dewormers—and their label claims—are highly regulated by the Food and Drug Administration.

Download the full dewormer chemical classes chart >>

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