Professor H. D. Chapman
Use of anticoccidial drugs in the USA
Two categories of drug are employed by broiler producers to control coccidiosis in poultry, ionophore antibiotics and synthetic agents (chemicals). As in other Countries, the compounds most commonly employed in the USA are the monovalent ionophores (salinomycin, monensin, narasin) and occasionally the divalent ionophore lasalocid (1). Whereas ionophores are used in the starter and grower feeds, chemicals (nicarbazin, diclazuril, and zoalene) are mainly employed in the starter feed (1). A mixture of both types of drug (nicarbazin and narasin) is also available. The same drug (single drug program), or different drugs (“shuttle” program) may be incorporated in feeds for a single flock. Most producers also employ a rotation program in which a shuttle program is used in the spring and a single drug program during the summer, fall and winter months. Although ionophores are still widely used, they are not as effective as when first introduced and, if employed continuously, resistant strains of Eimeria may develop (2). The choice of chemical is difficult because drug resistance to them is widespread. Medication is most effective when the level of infection is low; proper attention should, therefore, be given to appropriate management and hygiene.