Eimeria tenella: development of resistance to arprinocid and decoquinate in the chicken.

Resistance to arprinocid was developed in Eimeria tenella after seven serial passages in chickens given progressively greater concentrations of drug. Resistance to the quinolone decoquinate developed after eight passages. These results taken together with the observation that resistance to both drugs developed within a year of their introduction suggest that some indication of the likelihood of the emergence, in the field, of resistance to a given drug, may be obtained by comparing it with a standard reference drug in experimental studies.