Magnesium Toxicity: Effect on Phosphorus Utilization by Broiler Chicks

Excessive dietary magnesium (Mg) (.3, .5, and .9% additions to a corn-soy basal diet) fed to broiler chicks was found to be cathartic and significantly decreased 28-day body weight, significantly increased mortality, and induced leg abnormalities. Increasing dietary phosphorus (P) significantly ameliorated the detrimental effects of Mg toxicity except at the highest Mg level (.9% addition). Increasing dietary chloride (Cl) significantly increased body weights of Mg intoxicated chicks and significantly reduced the hypermagnesemia induced by excessive dietary magnesium. Excessive dietary magnesium increases the need for dietary P. Failure to monitor Mg content of diets may contribute to the ambiguity of ascertaining the P requirement of domestic fowl.