Rotational Deworming can Promote Drug Resistant Parasites

thehorse.com June 29, 2015

Traditional parasite control programs involved rotating dewormers with a number of different products at regular intervals. At that time, most horse owners were concerned about Strongylus vulgaris (large strongyle bloodworm).

Thanks to that traditional approach, S. vulgaris infections don’t occur very often. The two-month schedule associated with rotational deworming worked well on strongyle eggs because it takes about that amount of time for reappearance after treatment.

While S. vulgaris is no longer a large threat, according to the American Association of Equine Practitioners (AAEP) Parasite Control Guidelines, horse owners should still take action against other parasites, including small strongyles (cyathostomins) and tapeworms (Anoplocephala perfoliata), which have been recognized as a potential cause of colic.

But many veterinarians are now recommending a different approach to deworming that is less likely to result in anthelmintic (dewormer) resistant parasites. If rotational deworming was so successful, why switch strategies now? Shouldn’t those same strategies work on other parasites? The answer, quite simply, is “no.”

“Calendar-based rotational deworming is an outdated practice,” says Hoyt Cheramie, DVM, an equine specialist for Merial Large Animal Veterinary Services. “That’s because the life cycles and biology of small strongyles and tapeworms are different from large strongyles, and the rotational strategies designed for them aren’t as effective at controlling small strongyles and tapeworms.”

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April 23, 2016

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