Moderation of Monensin-Induced Growth Depression by Dietary Potassium

Abstract Experiments were conducted to investigate further an interrelationship between dietary composition and response of chicks to monensin. In three experiments with broiler chicks where a monensin level of 100 or 100 and 120 pp m was fed, no significant (P>.05 ) growth depression was observed regardless of dietary composition. In other experiments, 140 or 160 ppm monensin significantly depressed growth rate, and the depression with 160 ppm was significantly greater when the diets contained either 20% fish meal or poultry by-product meal than when a diet with no animal protein was fed. In another experiment chicks were fed to 4 weeks either a cornsoy diet (CS) or an isocaloric diet with 20% fish meal (FM) containing concentrations of either 0, 120, or 160 mg monensin/kg and either 0 or .3% added K (as carbonate). Growth rate of chicks fed the FM diet with the highest monensin level was significantly depressed below all other treatments, but adding K counteracted the growth depression. Another factorial experiment (2 × 2 × 2 × 3) was conducted comparing the CS and FM diets with monensin concentrations of 0, 120, and 160 mg/kg, added K concentrations of 0 and .3%, and dietary sodium levels of .18 and .28%. With respect to main effects on growth rate, monensin significantly depressed it and potassium increased it, but no significant effects were observed with diet or Na supplementation. A significant interaction between monensin and K was observed. Similar effects were observed with feed/gain ratios except that a significant diet times K interaction was obtained. These results suggest that the growth depression sometimes observed in commercial broilers fed diets containing monensin may be eliminated by dietary supplementation with potassium carbonate or other changes in ration formulation.