No abstract

Anthelmintic resistance (AR) in gastrointestinal nematodes of cattle is becoming increasingly prevalent worldwide, so there exists a need to develop novel approaches to manage and slow this progression. Refugia are the proportion of the worm population not selected by drug treatment, and the greater the proportion of the worm population left untreated (in refugia), the slower the progression of AR. Sources of refugia include worms in animals left untreated, stages of parasites not affected by the treatment, and free-living stages in the environment (e.g. eggs/larvae on pasture). Studies in sheep demonstrate that managing refugia will reduce the progression of AR without negatively impacting the health or productivity of the flock. However, many of these strategies are impractical for use with cattle, and consequently have not been tested or widely implemented in cattle. One refugia-based strategy with good potential applicability to the cattle industry is 'selective non-treatment’ where a percentage of the herd is deliberately left untreated. In this study, we examined the use of a selective non-treatment strategy in Stocker cattle.