STUDIES OF RESISTANCE TO ANTICOCCIDIALS IN EIMERIA FIELD ISOLATES ANDPURE EIMERIA STRAINS

Ten Eimeria field isolates from North Germany were studied in battery tests for sensitivity to selected anticoccidials. A high percentage of the Eimeria field isolates (9 out of 10) showed resistance to anticoc cidials, mostly multiple resistance. Partial or complete resistance to maduramicin was found in 7 field isolates, to monensin in 6, to salin omycin in 5, to nicarbazin in 8: to halofuginone in 7, to robenidine a nd toltrazuril in 1, and to diclazuril in 2 field isolates. Multiple r esistance had developed in 7 of the 10 isolates. Cross-resistance betw een maduramicin, monensin, and salinomycin occurred in 5 Eimeria isola tes. One isolate showed cross-resistance between diclazuril and toltra zuril. From the resistant isolates 15 pure E. acervulina and 5 pure E. brunetti strains were obtained by single oocyst infections. Seven of the E. acervulina and 4 of the E. brunetti strains showed resistance o r partial resistance that was also present in the original isolate. Te n of 11 resistant strains were multiply resistant.