Killing Resistant Parasites


"Parasite resistance has emerged as a dilemma in the livestock industry as many classes of parasites are becoming resistant to dewormers," began Meghan Blanek, graduate student in the Department of Animal Science at Texas Tech University. Her research found a deworming regimen that would decrease parasite resistance in horse herds.

"Reports of resistance to benzimidazoles in the literature are frequent in herds administered benzimidazole products for a significant period without rotation of different classes of anthelmentics or with frequent dosing intervals," said Blanek.

Blanek's study involved 13 mares, three yearlings, and 12 weanlings given only fenbendazole for 18 months prior. When using a fecal egg count reduction test (FECRT), the horses showed resistance.

A quarterly rotation was used by treating the horses with pyrantel pamoate in June, ivermectin/praziquantel in September, and fenbendazole in December, said Blanek.

Results showed that the horses had higher FECRT than before the study, and no significant difference in efficacy exhibiting a greater than 98% efficacy.

"This study showed that fenbendazole resistance in a herd can be broken with rotation of anthelmintic classes, and that fenbendazole can be effectively implemented in a future rotation program," she said.

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About the Author

Marcella M. Reca Zipp, MS

Marcella Reca Zipp, M.S., is a former staff writer for The Horse. She is completing her doctorate in Environmental Education and researching adolescent relationships with horses and nature. She lives with her family, senior horse, and flock of chickens on an island in the Chain O'Lakes.

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