Manganese utilization in the chick: effects of excess phosphorus on chicks fed manganese-deficient diets

Young chicks were used in a 16-d feeding study to evaluate the effects of excess dietary P on Mn utilization. The basal casein-dextrose diet (1.4 mg Mn/kg) was supplemented with 0, 3.5, 7.0, or 10.5 mg Mn/kg from MnSO4.H2O and was fed in the absence or presence of .8% excess dietary P (equal P contributions from KH2PO4 and NaH2PO4). Diets containing .8% excess P were also supplemented with .8% excess Ca (CaCO3) to keep the Ca:P ratio above 1:25 so as to prevent anorexia associated with excess dietary P per se. Both growth rate and total tibia Mn responded linearly (P < .01) to Mn supplementation in chicks fed the normal level of P, but those fed excess P responded erratically. Excess P did not affect growth or tibia Mn in chicks fed the basal diet, but birds fed diets with supplemental inorganic Mn grew slower (P < .01) and had lower (P < .01) quantities of Mn in tibia when excess P was supplemented. Manganese content in the tibia of chicks fed excess P was 55% of that in chicks fed an adequate level of P.