The Past, Present, and Future of Equine Deworming

Parasitologists now recommend deworming based upon the each horse’s needs, determined by fecal egg counts.

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Forty years ago, Don McLean was singing "Bye, Bye Miss American Pie" on the radio, gas was 55 cents a gallon, just 52% of American households had color television sets, and rotational deworming was considered the best and most efficient treatment for equine parasites. Not anymore.

"Horse owners should be saying ‘bye, bye’ to the outdated practice of calendar-based rotational deworming," says Hoyt Cheramie, DVM, MS, equine specialist for Merial’s Large Animal Veterinary Services. "We have new science that tells us there is a better, more effective way to control parasites in horses."

Where We’ve Been
In 1966, Gene Lyons, PhD, and Harold Drudge, DVM, introduced an equine parasite control program designed to suppress large strongyles, the most prevalent and threatening equine parasite at the time. Using information then available, they proposed a simple formula: treat every horse on the property the same–deworming every other month, year-round. They also suggested alternating between products to target all parasites.

Horse owners began adopting their suggestions. Then, as new drug classes came on the market, pyrimidines (pyrantel) in the 1970s and avermectin/milbemycins (ivermectin and moxidectin) in the 1980s/90s, rotating between products became even easier, making the practice widely suggested by veterinarians and a standard way of deworming among horse owners

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