Approaches for testing worms for drench resistance include assays conducted on worms of specified life cycle stages in the laboratory to determine the proportion of worms killed by varying concentrations of anthelmintic. These assays include the egg hatch assay (EHA) to detect resistance against benzimidazoles (BZ, white drenches) and the larval development assay (LDA) to detect resistance against benzimidazoles (BZ, white drenches) and levamisole (clear drenches). These assays are largely used as research tools.
DNA tests have been developed to detect resistance to the benzimidazole (BZ, white drench) anthelmintics. As the technology becomes cheaper, genomic tests will likely replace more labour-intensive laboratory assays. The mutations responsible for macrocyclic lactone (ML) and levamisole resistance are not known, so currently no DNA tests are available to assess resistance to these chemical groups.