Comparative efficacy of anticoccidials under the conditions of commercial broiler production and in battery trials.

Coccidia were isolated from a commercial broiler farm with a history of suspected drug resistance. The sensitivity profiles of the Eimeria spp. isolates against the anticoccidial drugs nicarbazin (NIC), narasin (NAR), halofuginone (HAL), salinomycin (SAL), meticlorpindol plus methylbenzoquate (MET), and monensin (MON) at the recommended dose levels were followed in three battery trials (B1, B2, B3) corresponding to a field study over three periods of commercial broiler keeping (F1, F2, F3). Shuttle programs were performed in F1 (NIC/MON) and in F2 (MET/MON) while only SAL was used in F3. Eimeria acervulina and E. tenella were isolated from indicator birds in F1 while only E. acervulina could be found during F2 and F3. In trial B1 the isolate from F1 was identified as resistant against HAL and partly resistant against NIC and MON, the two drugs that were used in F1. Following the replacement of NIC in the starter feed by MET the respective isolate from F2 showed no resistance against ionophores (trial B2) while partial resistance against HAL was still present. Since SAL was the most efficient drug in B1 and B2 only this drug was applied in F3. Apart from a resistance against HAL no resistance against any of the other tested anticoccidials was found in the isolate from F3. SAL controlled coccidiosis efficiently in the field and best productivity was recorded in F3. This study shows that battery trials have a good predictive value in respect to the efficacy of anticoccidials under the conditions of commercial broiler production.