Anthelmintic resistance of bovine gastrointestinal nematodes to macrocyclic lactones in Japan

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Fecal egg count reduction tests using ivermectinpour-onformulation were conducted to investigate the prevalence of anthelmintic resistance in gastrointestinal nematodes on cattle farms in Aomori and Hokkaido, northernJapan, in 2009 and 2010.The egg count reductionsof predominant infecting nematodes, Cooperiaspp., were lower than90% on one farm in Aomori and two farms in Hokkaido after ivermectin treatment on August. The egg count reductions below 90% strongly suggest the presence of anthelmintic resistance. This is the first confirmation of ivermectin-resistantnematodes in cattle in Japan.