Response of 21 Canadian field isolates of chicken coccidia to commercial anticoccidial drugs.

Coccidia were isolated from 30 broiler farms in major poultry-producing provinces of Canada; 21 mixed-species isolates were tested for sensitivity to anticoccidial drugs. Eimeria acervulina was identified in 20 samples, E. maxima in 15, and E. tenella in 10 of the mixed-species isolates. On the basis of weight gain after infection, 3 isolates were judged sensitive to amprolium, 5 to monensin, 9 to salinomycin, 14 to lasalocid, 19 to halofuginone, and 20 to nicarbazin. Similar trends in sensitivity/tolerance were identified from the percent reduction of intestinal lesion scores of medicated birds compared with scores of unmedicated, infected controls. These results were consistent with the previous pattern of use of anticoccidial drugs in commercial poultry in Canada.