Calcium turnover in different bone segments of laying fowl

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Abstract
The turnover of calcium in various bone segments was studied by a single-dose technique in Nicarbazin-treated hens, and by a long-term feeding of a Ca45-labeled diet in normal laying hens. Nicarbazin treatment prevented ovulation and shell formation with only a slight effect on plasma Ca concentration. In the treated hens, exchangeable Ca comprised 3.3%, 0.5%, and 5.2% of the Ca in femur ends, cortical, and medullary segments, respectively. Accretion rate was highest in the medullary and lowest in the cortical segment. Results of the long-term Ca45 feeding indicate the following sequence for the turnover rate of Ca in bone segments: tibia medullary = femur medullary >> femur ends > tibia ends = sternum > humerus ends > femur cortical > tibia cortical = humerus cortical. During a 12-day period at least 70% of Ca in the medullary segment was replaced. On continuous feeding of Ca45 to laying hens, plasma and egg-shell specific activity reached a maximum level, higher than that of the diet, between 12 and 20 days.