SENSITIVITY OF FIELD ISOLATES OF EIMERIA TO MONENSIN FOLLOWING THE USE OF A COCCIDIOSIS VACCINE IN BROILER-CHICKENS

The sensitivity of field isolates of Eimeria to monensin was investiga ted following the use of a commercial coccidiosis vaccine. Monensin wa s not effective against isolates from five commercial farms where iono phores had been used for many flocks. Monensin was more effective, how ever, against isolates obtained from the same farms following the use of a coccidiosis vaccine. No further improvement in drug efficacy was noted after five successive flocks in which the vaccine was used.