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DURING egg formation, large quantities of calcium are deposited as carbonate on the developing shell. The site of shell formation, the oviduct shell gland, is not a calcium storage organ; consequently, calcium must be mobilized rapidly from body stores to meet the periodic requirements of shell formation. Since the body calcium is located almost entirely in osseous tissue, it must pass through the circulatory system in rather large quantities during each period of active shell formation (about 14 hours; Bradfield, 1951). There is also an increase in calcium absorption from the gut during shell formation (Buckner et al., 1930), which contributes to the fluctuation in blood calcium concentration. The literature contains several reports of the influence of shell formation on blood calcium. Charles and Hogben (1933) found that plasma calcium concentration during egg formation was about 20% higher than during non-laying periods. However, their data for hens with a forming . . .
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Winget et al. (1958) studied this question.
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