Facts and fiction regarding anthelmintic efficacies in cattle

an updated assessment

Abstract

Very few label claims for cattle anthelmintic efficacies are factual under all circumstances. This is because: 1) no new class of anthelmintic has been commercialized in the USA since the mid 1980s; 2) worm populations are forced into selection for resistance every time a bovine is treated; 3) some resistant female worms can void >2000 eggs per day; and 4) rarely are anthelmintics given at the farm level wherein sustainable effectiveness is safeguarded. Given the above, it is not shocking that most label claims of effectiveness and persistence for ALL anthelmintics (endectocides, flukicides, and nematocides) are currently overstated. Lack of excellent nematocidal efficacies has been either accepted as normal or overlooked by cattle people, a state of affairs made possible by the fact that bovine nematodiasis is largely a subclinical condition. Lack of anthelmintic efficacy is not connected to suboptimal animal performance. Routinely, there is no "real world” quantification ofthe detriment caused by post-treatment worm burdens; an observation primarily reserved for research projects. The efficiency of the cattle industry (beef and dairy) and the per-animal productivity in the US have been on a steady rise for decades, due in large part to advances in nutrition, genetics, husbandry, and disease control. Unfortunately, the trend in effective chemical control for parasites over the same period has been in the opposite direction. Advances are sorely needed in both chemical and non-chemical (husbandry, vaccine, biological, nutriceutical, genetic) parasite controls. In this paper, a few observations will be made on anthelmintic efficacies, and the impact of ineffective nematocidal control.