Progress in the control of coccidiosis with anticoccidials and planned immunization.

New anticoccidials continue to be introduced to the poultry industry on an average of about one every 2 years. Revised requirements have increased costs of discovery, development, and approval by the Food and Drug Administration to several million dollars for each product. Gross sales of anticoccidials are now estimated to be in excess of $30,000,000 annually. Anticoccidials are almost universally used in starter rations for meat-type birds being raised under floor-pen management. Protection is more important with these fast-growing birds than with egg-producing types where immunity and cage layer management modify demands for anticoccidials. Coccidiosis mortality has generally been eliminated by all 25 approved anticoccidials if properly used. Selection of specific anticoccidials is based on the ability of the anticoccidial to: (1) improve weights and (2) feed conversion, and (3) to suppress development of lesions. Costs of the product may influence decisions on which one to use. With some anticoccidials the rapid emergence of drug resistant strains has been the biggest problem. "Switching" among the 13 classes of anticoccidials and the so-called "shuttle program" are common methods used to avoid development of resistance. Preventive medication will probably continue to constitute the major method of coccidiosis control with meat-type poultry if attempts to develop economic cage-type management do not supplant current litter and floor-pen management. Immunity acquired through incidental or planned immunization is more important in control of coccidiosis with layer and breeder flocks raised in floor-pens. Some progress in development of avirulent immunogenic strains of different species of coccidia has been reported and further research efforts in this direction should be encouraged.