Calcium metabolism in laying hens. 5. Calcium balance and mobilization of calcium sources for eggshell formation.

and reviewed by SIMKISS17) and PETERSEN15), recently. It has been known that calcium metabolism is affected by genetical, physiological and environmental factors in addition to a number of nutritional factors. MUELLER et al.13) stated that less observations were obtained on the principal pathway and biokinetic aspects of calcium metabolism in laying hens, and their data gave many informations on these problems. The exact amount of calcium obtained from the bone and directly from the diet for eggshell formation varies considerably as a result of many factors concerning the calcium metabolism and is not known specifically. In previous reports by ITOH and HATANO10,11), the effects of time of feed intake (morning and evening) for eggshell deposition and excretion of calcium, and the changes in eggshell deposition of radiocalcium during the shell formation period of an egg were discussed on two groups of laying hens during 10-day period with radiocalcium administration and following 10-day period without Ca45 administration. The objectives of report presented here are: (a) to determine the calcium and radiocalcium balance and find the quantitative aspects of calcium metabolism in laying hens; and (b) to discuss the changes in the quantitative mobilization of the calcium sources for eggshell formation, on the basis of data in the experiment previously reported10,11).