Sensitivity of field isolates of Eimeria from two broiler complexes to anticoccidial drugs in the chicken.

The spectrum of resistance to seven currently used anticoccidial drugs in isolates of Eimeria obtained from farms two broiler complexes was examined. All isolates were resistant to monensin, salinomycin, and narasin. Lasalocid was more effective in controlling coccidiosis than the other ionophores, although most isolates were classified as resistant to the drug. The majority of isolates were sensitive or showed reduced sensitivity to robenidine, clopidol, and decoquinate. It was concluded that for drugs that have been used extensively (e.g., monensin and salinomycin), examination of isolates from one or two farms may give results applicable to the entire complex. For drugs that have been used infrequently, however (such as robenidine, clopidol, and decoquinate), examination of isolates from at least five farms would be desirable to establish the spectrum of drug sensitivity.