Reduction of anticoccidial drug resistance by massive introduction of drug-sensitive coccidia.

Massive introduction of a drug-sensitive attenuated strain of Eimeria tenella in a floor-pen heavily contaminated with a drug-resistant strain produced a marked reduction in the proportion of drug-resistant oocytsts in the litter. This provides a useful adjunct to planned immunization programs since the procedure protects the birds against subsequent challenge through immunity imparted by the introduced strain while restoring the effectiveness of the anticoccidial drug which was previously ineffective because of the predominance of drug-resistant coccidia.