Magnesium metabolism in the laying fowl

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Abstract
Laying fowls were fed on synthetic diets containing 49, 118, 486, 655, 1242 and 2176 mg/kg magnesium. Magnesium intake and plasma concentration were significantly correlated: 49% of the plasma Mg was diffusible. The hens fed on magnesium‐deficient diets (49 to 118 mg/kg magnesium) were hypomagnesaemic while those receiving 2176 mg/kg were hypermagnesaemic. In the deficient hens the liver showed magnesium depletion, increased calcium content and decreased fresh weight. Skeletal muscle was unaffected by the dietary variations in Mg. The magnesium concentration in the femur was positively correlated with the plasma magnesium concentration. Femurs showed a loss of magnesium and increased mineralisation (especially of the medullary bone) in deficient hens, and a net gain of magnesium in the birds receiving 2176 mg/kg magnesium. The magnesium concentrations in egg shells, albumen and yolk were also positively correlated with the plasma magnesium concentration. The shells of eggs laid by magnesium‐deficient hens were thin, a reflection, apparently, of the reduced plasma calcium levels associated with the decreased bone mobilisation.