Herding the U.S. cattle industry toward a paradigm shift in parasite control.

Contemporary management of nematode parasitism in cattle relies heavily on a single class of drugs, the macrocyclic lactones (MLs). The potency and convenience of the MLs, along with the low cost of generic formulations, have largely supplanted the need for critical thinking about parasite control, and rote treatment has become the default 'strategy'. This approach to parasite control has exerted substantial pressure to select populations of nematodes that can survive recommended dosages of ML products. Although macrocyclic lactones have been available for over 30 years, putative ML resistance in U.S. cattle was not reported until fairly recently. This pattern begs the question, "Is this a new, emergent problem, or an old issue that is finally commanding some attention?" The implications of bovine anthelmintic resistance should stimulate a paradigm shift for U.S. cattle producers and their advisors. However, there are significant obstacles to changes in current thinking. It is anticipated that cattle producers will be extremely reluctant to abandon historical practices unless they can be convinced of the value of alternatives that are communicated through targeted education, practical demonstrations, economic analyses, and scientific evidence. Historically, the management advice of practitioners has not relied strongly on parasite epidemiology, and practitioners may not have the knowledge to implement evidence-based recommendations. Pharmaceutical companies could play a significant role in helping to shape and shift the thinking about sustainable use of anthelmintics. However, their primary responsibility is to stockholders, and they have strong economic incentives for maintaining the status quo. It is complicated and difficult to change attitudes and practices, and it will take more than logic or fear to shift the parasite control paradigm in the U.S. cattle industry. Achieving that goal will require collaboration among stakeholders, a consistent, straightforward and understandable message about resistance, and recommendations that are practical as well as effective. But if we hope to ultimately influence producers and their advisors, we need to be conscious of how individuals and groups change their minds.
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