Bone composition and Ca45 retention in fowl as influenced by egg formation

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Abstract
Ca45 was intravenously administered to laying hens close to the time of ovulation. Groups of five birds were killed at intervals ranging from 30 min to 14 days, after dosing, and calcium, phosphorus, and radioassays were made on their blood plasma, on ends and cortical and medullary segments of their tibias and femurs, and on eggs laid previous to killing. Radioactivity in blood plasma and eggs decreased with time. There were no significant changes in amount and calcium and phosphorus content of tibia and femur segments during one and more reproductive cycles. Radioactivity of bone segments increased to 2 hr after dosing and later markedly declined, paralleling eggshell deposition. Specific activity of the medullary segment was higher than that of ends or cortical segment. It is suggested that the decline in radioactivity of bone is caused mainly by exchange with stable calcium during its transfer from gut to eggshell, although resorption of bone may also take place. The high specific activity of medullary bone 2 days after dosing suggests a greater turnover of calcium in this segment than in the other segment studied.