evaluating the resistance of eimeria spp. field isolates to anticoccidial drugs using three different indices.

background: in this study, the presence of resistance to diclazuril, amprolium+ethopabate and salinomycin, representing some of the commonest anticoccidials in iran’s poultry industry, against three mixed eimeria field isolates were investigated. methods: three eimeria field isolates, collected from typical broiler farms in iran, were propagated once, inoculated to 480 broilers, comprising 30 chicks in each treatment. the non-medicated or medicated diets containing one of the above mentioned anticoccidials were provided ad-lib . drug ef-ficacy was determined using the global index (gi), anticoccidial sensitivity test (ast) and opti-mum anticoccidial activity (oaa). results: none of the field isolates were fully sensitive to the selected anticoccidials. all isolates showed reduced sensitivity/partial resistance to salinomycin. resistance to amprolium+ethopabate was evident and partial to complete resistance was recorded for diclazuril. conclusion: limited efficacy of the selected anticoccidials is obvious. considering the cost of conti-nuous use of anticoccidials in the field, altering the prevention strategy and rotation of the anticocci-dials with better efficacy, would prevent further economic losses induced by coccidiosis.