Effect of dietary ingredients on monensin toxicity in chicks

A corn-soybean (CS) diet and diets containing medium or high levels of animal protein (AP) calculated to contain the same concentrations of the main nutrients promoted essentially the same growth rate and feed utilization in 20-day-old chicks. Supplementation with monensin sodium (100 or 120 mg/kg) depressed growth rate of the chicks fed all three diets. However, effect of the drug was much more severe in chicks fed the diets containing AP. This interaction resulted in significant (P < .05) differences in body weights between chicks fed the CS diet and PA diets. Moreover, feed-to-gain ratio was significantly (P < .05) adversely affected by monensin only in chicks fed the AP diets. Supplementation of the high AP diet with extra vitamin E, a mixture of arginine and tryptophan, or a mixture of silicon, chromium, and molybdenum failed to prevent the growth depression caused by monensin. These studies demonstrate that ingredient composition of diets for broiler chicks affects the magnitude of growth depression caused by monensin supplementation.