Manganese turnover in chicks as affected by excess phosphorus consumption

A repletion-depletion assay was conducted to evaluate the effect of Mn status and excess dietary P provided as dicalcium phosphate on Mn excretion and turnover. Chicks were fed either Mn-adequate (30 mg Mn/kg) or high Mn (1000 mg Mn/kg) casein-dextrose diets for 7 d. Following this loading period, the chicks were fed a Mn-deficient casein-dextrose diet (1.4 mg Mn/kg) with or without 0.5% excess P supplied from dicalcium phosphate. Whole body (without feathers) and selected body tissues (liver, kidney, gut, tibia and feathers) were assayed for Mn content at 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 15 and 20 d after initiation of the Mn-deficient diet. Excess P had little effect on Mn turnover. All tissues showed significantly reduced biological half-lives (P less than 0.05) as a result of loading chicks with a high level of Mn (1000 mg/kg) during the 7-d loading period. However, there was wide variation in Mn turnover rates among tissues. Liver, kidney and whole body contained readily exchangeable manganese in much higher proportions than did bone.