Manganese utilization in chicks as affected by excess calcium and phosphorus ingestion

Three experiments were conducted to assess Mn utilization in the presence or absence of excess Ca and P from various sources. Supplements were added to a corn-soybean meal diet containing 1% Ca, .7% (.5% available) P and 37 mg of Mn per kg. Three percentages of supplemental Mn from MnSO4.H2O (0, 500, and 1,000 mg of Mn per kg) were used to construct a standard curve of tibia Mn regressed on the 14-day supplemental Mn intake (r averaged .96 for the three experiments). From this, the tibia Mn values obtained from chicks fed diets containing 1,000 mg of supplemental Mn per kg of diet plus 1% added Ca from various sources, were used to calculate bioavailable Mn via standard-curve methodology. In Experiment 1, analytical-grade (AG) CaCO3, feed-grade (FG) oyster shell and FG dicalcium phosphate decreased Mn utilization by 20, 15 and 53%, respectively, but FG limestone was without effect. Experiments 2 and 3 were conducted to determine how different combinations of Ca and P, as well as different cationic forms of P, affected Mn utilization. The results from these experiments indicated that feeding .88% of excess inorganic P, regardless of source and whether fed alone or in combination with excess Ca, reduced Mn utilization by 50 to 65%. Among the Ca sources, only oyster shell caused a reduction in Mn utilization. It is evident that excess dietary P is more antagonistic to Mn than is excess Ca.