Antiparasitic resistance and grazing livestock in the United States (JAVMA, Vol 244, No. 9, May 1, 2014)

Antiparasitic resistance, specifically resistance to anthelmintics among gastrointestinal parasites of cattle, small ruminants, and horses, is both a health and a welfare issue for US grazing livestock and potentially threatens animal agricultural production. The veterinary community broadly accepts that antiparasitic resistance is widespread among small ruminant parasites, particularly in Australia, New Zealand, South Africa, and some South American countries. And, many veterinarians and livestock producers acknowledge that antiparasitic resistance is also a problem among small ruminant parasites in the United States. However, awareness of antiparasitic resistance in cattle and horse parasites in the United States and other countries is relatively low, even while reports of resistance involving parasites of these species are increasing. Although the FDA Center for Veterinary Medicine (CVM) determines whether antiparasitic drugs for animals are safe and effective before approval, the drugs’ continued effectiveness after approval largely depends on how they are used by veterinarians and producers.

As a consequence of sole reliance on the use of antiparasitic drugs for parasite control and other unsustainable management practices, such as treating entire herds on the basis of set protocols instead of actual need, widespread resistance to all major families of broad-spectrum anthelmintics may develop in the near future. To help combat this threat, the CVM has developed an outreach initiative to educate veterinarians and livestock producers on how to integrate selective antiparasitic drug use with sustainable management practices. The goal is to maintain the effectiveness of current antiparasitic drugs for as long as possible. As part of this initiative, the CVM has been collaborating with other regulatory agencies, veterinary professional organizations, livestock producer groups, the animal drug industry, researchers, and educators on efforts to slow the development of resistance among parasites affecting US grazing livestock.

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