Phosphorus, but not calcium, affects manganese absorption and turnover in chicks

Two balance studies with growing chicks were conducted to evaluate the effects of excess Ca or excess P on endogenous fecal Mn excretion and true Mn absorption. An isotope-dilution technique was used to estimate endogenous manganese in excreta. Supplements were added to a corn-soybean diet containing 1% Ca, 0.7% P (0.5% available P) and 37 mg Mn/kg. In Experiment 1, supplemental Ca levels of 0, 0.5 and 1.0% from feedgrade limestone were compared. True absorption of Mn was not affected by Ca level (P greater than 0.10) and averaged 2.8% for birds fed the Mn-unsupplemented diet. In Experiment 2, a 2 x 3 factorial arrangement of treatments included: 100 and 1000 mg/kg supplemental Mn (from MnSO4.H2O) and 0, 0.4 and 0.8% added P supplied by dicalcium phosphate. Excess P significantly decreased true absorption of Mn (P less than 0.01). In birds fed 100 mg/kg supplemental Mn, absorption of Mn decreased 22% as excess P increased from 0 to 0.8%, whereas in birds fed 1000 mg/kg supplemental Mn, Mn absorption decreased 59% as a result of 0.8% P supplementation. These results confirm that the antagonism of Mn by inorganic P is due to reduced gut absorption of Mn.