Differences between the anticoccidial potencies of monensin in maize-based or wheat-based chicken diets

Experiments were carried out to investigate why the anticoccidial ionophore monensin is more potent against the coccidium Eimeria tenella in chickens fed on a maize-based diet (as in the USA) than in chickens fed on a wheat-based diet (as in the UK). The explanation seems to be that the pathogenicity of E. tenella is lower in maize-fed chickens than in wheat-fed chickens, whether monensin is present in the diet or not. Possible reasons for this are suggested. The better survival of maize-fed birds may be partly due to protective effects of the higher concentrations of vitamins A and E derived from their diet. Furthermore, the higher concentrations of niacin and riboflavin in wheat than in maize may enhance coccidial pathogenicity. These opposing factors might combine to cause equivalent infection levels to produce more severe coccidiosis in chickens fed on a wheat-based diet than on a maize-based diet.