These Ain't Your Father's Parasites: Dewormer Resistance and New Strategies for Parasite Control in Horses

Most veterinarians continue to recommend anthelmintic (dewormer) treatment programs for horses that are based on knowledge and concepts that are more than 40 years old. However, recent studies demonstrate that resistance and multiple-drug resistance in equine parasites is extremely common, but few horse owners or veterinarians take this into account when making treatment decisions. Parasites are highly over-dispersed in hosts, such that a small percentage of hosts (20%) harbor most (80%) of the parasites. The common practices of recommending the same treatment program for all horses despite great differences in parasite burdens, of recommending frequent preventive treatment of all horses without any indication of parasitic disease or knowing what species of parasites are present, of recommending the use of drugs without knowledge of their efficacy, of failing to perform fecal egg count surveillance and of failing to determine if treatments are effective, are all incompatible with achieving optimal and sustainable parasite control. Consequently, it is necessary that attitudes and approaches for parasite control in horses undergo a complete overhaul, and that both horse owners and veterinarians become educated in these important issues.