Fenbendazole at triple the normal dose would not control O. circumcincta. Anthelmintic resistance, once established, thus appears to be fairly stable and long lasting. Use correct doses of anthelmintics . Easier said than done. Avoid too frequent treatments .
Genes expressing resistance are normally at a low frequency in a population of nematodes.
Frequent use of an anthelmintic increases the frequency of these resistant genes since the resistant survivors of treatment become more numerous in succeeding generations and eventually become the dominant strain in a population. If the treatment interval approaches the prepatent period of a nematode then the whole population is exposed to the drug in the course of a grazing season. As a result, the population of free-living stages rapidly becomes one derived from nematodes that have survived exposure to the anthelmintic. Therefore, drug control programs should be based on a minimum number of treatments. Rotate drugs .