Isolates of Eimeria tenella: studies on resistance to ionophorous anticoccidial drugs

Four isolates of Eimeria tenella obtained from the field were partially resistant to monensin. This resistance was not lost after 10 passages in unmedicated chickens, indicating that it was stable. One of the four isolates was examined and found to be resistant also to narasin, salinomycin and lasalocid.