Effect of Dietary Magnesium and Fluoride on Bone Mineralization in Young Chicks

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Abstract
Tracer techniques were used to examine the reduced bone mineralization observed in young chicks fed diets elevated in both magnesium (4500 ppm) and fluoride (800 ppm). The distribution of 45Ca 1 hour after injection of the isotope into a ligated intestinal segment was examined in 2-day-old chicks fed control and high magnesium plus high fluoride diets. Although no differences in intestinal absorption were observed, decreased femur uptake and increased plasma levels of 45Ca were found in the chicks fed the high magnesium plus high fluoride diets. At an early age (2 to 6 days) chicks fed the high magnesium plus high fluoride diets incorporated less 45Ca and 32P into their femurs 4 hours after intraperitoneal injection when compared with chicks maintained on control, high fluoride or high magnesium diets. As a result of the reduced femur 45Ca incorporation, plasma 45Ca levels were elevated in the high magnesium plus high fluoride group. At later ages (8 to 10 days) incorporation of injected 32P into femurs was not affected by dietary treatment, but 45Ca incorporation was elevated in the high magnesium plus high fluoride group. Analysis of plasma and soft tissues for calcium revealed no treatment differences at 4 days, but 45Ca levels in plasma 4 hours after intraperitoneal injection were elevated above control values at every age studied. Results of in vitro studies have suggested that bone from chicks in the magnesium plus fluoride group incorporate less 45Ca and 32P than bones from chicks in the other groups when incubated in plasma of chicks from the same treatment.