Parasite drug resistance is on the rise. While horse-care patterns usually evolve over decades, we could be facing a radical change in the way we deworm our horses because the comfortable methods that we’ve used for a quarter century actually may be harming our horses. Our familiar deworming schedules may need to be replaced, and egg counts should help us decide which drugs to choose.
When paste deworming arrived and went directly into the hands of horseowners, parasite-related illnesses among horses declined. Caring vets cheered. (Some veterinarians, motivated more by money, weren’t as enthusiastic.) Worm worries appeared to be history.
Now it seems that the quick squirt-and-be-done home procedure could have backfired. We���re overdoing it, and we’re not getting veterinary feedback when we choose a drug. We might not be using the right drugs for the right worms, and we might be creating resistance among parasites, too. While resistance to pyrantel, the drug found in daily dewormers, probably doesn’t surprise anyone — after all, it’s the same drug given day after day — it’s surprising that a constant rotation of different drugs might have a similar effect.
Horse Journal has received requests for a revised schedule for deworming that readers can just pin on the barn bulletin board to use. Praziquantel — the tapeworm drug found in ComboCare, Quest Plus, EQuiMAX, Zimectrin Gold — wasn’t available the last time we did a deworming schedule. However, our veterinary editor Dr. Eleanor Kellon concluded that deworming isn’t that simple anymore.
We need to consider using a “slow rotation” process, one that the cattle world has been using for some time. This means we choose one drug and use it for a full year, then rotate it with another drug for the next year, and so on (except, of course, for getting bots and tapes).
We’re also learning that we may do our horses a favor by not deworming as often. Instead, we should check to see if the horse needs deworming. (Sort of reminds us of blood titers and vaccines, doesn’t it’) In order to protect our horses from parasites, we’re going to need parasite-egg counts.
Change is never easy, especially when it involves something you’ve believed for decades. Heaven knows, I’m not looking forward to taking a plastic bag of manure to the vet’s office several times a year. However, bringing the vet back into the deworming process is a real bright spot. It’s the best form of preventative medicine we could administer.
-Cynthia Foley
