Regulation of net intestinal calcium uptake in hens laying obligatory soft-shelled eggs.

1. Individually caged laying hens had a loop of thread inserted into the shell gland. This resulted in the laying of soft shelled eggs. 2. A balance study was performed for a one week period before and after the operation. After the operation birds with threads consumed less calcium than before. Their requirements for calcium for eggshells decreased, resulting in increases in both calcium excreted and calcium retained. 3. Net calcium extraction in the digestive tract was measured in groups of birds with threads and intact controls, when shelling or not, by examining ratios of Ca to TiO2 in different gut segments. Observations were made during the period following premature oviposition in birds with threads, but within the normal shelling period of control birds. The period of study was at least two weeks after the operation. 4. Birds with threads absorbed less calcium than control birds up to the upper jejunum. 5. Control birds secreted calcium between the upper jejunum and colon, but birds with threads showed little change in absorption in this part of the digestive tract. 6. The increase in calcium absorption in intact birds was a response to the stimulus of shelling an egg or replacing calcium in medullary bone during a pause day, rather than of ovulation.