Anticoccidial Drug Resistance: Differences Between Eimeria acervulina and E. tenella Strains Within Broiler Houses

ABSTRACT Differences between the anticoccidial drug resistance of Eimeria acervulina and E. tenella strains to Bonaid (0.01 l%),Coyden (0.0125%), and Deccox (0.003%) were evaluated in mixed species cultures isolated from 155 different broiler houses. Drug-resistant E. tenella strains were not found in cultures containing drug-sensitive E. acervulina. Interspecies differences, characterized by drug-sensitive E. tenella in the presence of drug-resistant E. acervulina, were found in cultures from 8 of 31 (25.8%) flocks being medicated with Coyden, and in cultures from 30 of 52 (57.7%) flocks medicated with another anticoccidial(s) following exposure to Bonaid, Coyden, or Deccox. These differences were attributed either to a faster rate of drug resistance development in E. acervulina, or the introduction of drug-sensitive strains during periods of exposure to another anticoccidial(s). Lengthening the period of exposure to a secondary anticoccidial(s) increased the likelihood of recovering drug-sensitive strains