Calcium turnover in different bone segments of laying fowl

¹ The Volcani Institute of Agricultural Research, The National and University Institute of Agriculture, Rehovot, Israel

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.

Key Words: calcium metabolism in avian species • calcium metabolism and egg-shell calcification • medullary bone and shell • calcification • utilization of dietary Ca⁴⁵

Submitted on May 27, 1964