With the growing number of parasite populations resistant to anthelmintics, today’s parasite control programs require more thought and planning than simply deworming all horses in a herd every other month. Fecal egg count testing, selective deworming, and environmental controls can help you create an individualized–and effective–program for your farm and your horses.

Putting this type of deworming program in place takes some upfront effort and cost, but it can save horse owners money in the long run, and more important, it might help delay the emergence of parasites that are resistant to the available ¬anthelmintics.

"Most common equine parasites are resistant to at least one class of dewormer," says Craig R. Reinemeyer, DVM, PhD, president of East Tennessee Clinical Research Inc., in Rockwood, Tenn. "And it has to do with how intensely various products have been used. We need to deworm less, and we need to deworm more intelligently."

For a long time horse owners and farm managers thought the best way to control parasites was with drugs, drugs, and more drugs, but many parasites have consequently developed resistance to the dewormers we use, explains Ray M. Kaplan, DVM, PhD, Dipl. EVPC, professor of parasitology at the University of Georgia College of Veterinary Medicine in Athens. "The more often you deworm, the more drug resistance you will have," he says