Owners are often concerned about internal parasites–maybe a little too concerned–and their actions to rid horses of all parasites are leading to the unintended consequences of making some deworming products ineffective.

To get a better handle on controlling equine internal parasites, owners need to understand parasites, their life cycles, and the effects deworming has on a herd. Many oral medicines are available over the counter to treat common parasites, but the problem is they have been overused, fueling parasite resistance to these compounds.

Some owners believe if they don't deworm all of their horses frequently, then they are not doing everything they can to protect their horses, explains Debra Collins Ruffin Taylor, DVM, Dipl. ACVIM, an associate professor at Auburn University's College of Veterinary Medicine, in Alabama