Gram-positive bacteria (e.g., Clostridium perfringens – the cause of necrotic enteritis). Non-ionophores (chemical) anticoccidials These are compounds produced by chemical synthesis. Each anticoccidial in this category are quite different from each other and from ionophores. They either kill coccidia (cidal activity) or suppress coccidia (static activity). They have no known antibacterial activity and, hence, are not antibiotics. They are not used in human medicine and are classified as not medically important (category IV). What are the non-ionophore anticoccidials? They are products containing nicarbazin, amprolium, zoalene, decoquinate, clopidol, robenidine and diclazuril. Proprietary trade names, respectively, include: Nicarb, Amprol, Zoamix, Deccox, Coyden, Robenz and Clinacox. How do they work against coccidia? Unlike ionophores, each non-ionophore anticoccidial works against coccidia in a unique way; there is not a common mode of action. Generally, non-ionophores (chemicals) act by interfering with one or more stages of the life cycle of the parasite. Amprolium, for example, acts by providing a fake nutrient (vitamin B1) to the coccidia, starving them in the process. What should I know about them? Non-Ionophores are generally safe, but birds do not tolerate nicarbazin in hot weather. Also, there may be changes in eggshell colour as well as reduced fertility in reproductively active birds. All non-ionophore anticoccidials are approved for use in broiler chicken production but only amprolium, zoalene, robenidine and diclazuril are approved for use in turkey production. They all have a zero-day withdrawal except for Robenz (six days). Coccidia develop resistance to CANADIAN POULTRY 11 non-ionophores so each product should be used with careful planning. It is recommended to not use the same non-ionophore back-to-back for more than two grow-outs and also allow a one year rest period. The exception to this is nicarbazin, which has no reported development of resistance. It is important to note that cross-resistance does not develop with non-ionophore anticoccidials, making them invaluable in rotation programs. Although non-ionophores have been used in rotation programs for many years, the latest use is for reduction of the third peak of cycling in broiler chickens vaccinated against coccidiosis. To counteract the disadvantages (mortality, unevenness, wet litter, necrotic enteritis) of excessively high oocyst counts with cycling of coccidia, zoalene (non-ionophore) is being used to reduce the third peak of cycling. Note: zoalene is optimal for this purpose because it reduces the peak but does not entirely shut down cycling (development of immunity). Summary The Canadian poultry industry is fortunate to have a wide range of anticoccidials available to use in the prevention of coccidiosis and, indirectly, necrotic enteritis. Knowing whether a product is an ionophore or non-ionophore (chemical) is invaluable in designing rotation programs. We have to save the products we have now since each one has a contribution to make and there are no new ones on the horizon!