The absorption and excretion of minerals by laying hens in relation to egg shell formation

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Abstract
The absorption and urinary and faecal excretion of calcium, phosphorus, magnesium, sodium, potassium and chloride were studied in four colostomised laying hens during 24 hr periods. The urinary excretion of ammonia was also determined. Data for 10 laying and 5 non‐laying days were obtained. On laying days (a) net absorption of all minerals, expressed either as actual weights or as a percentage of intake was greater, (b) urinary excretion of phosphorus, potassium and ammonia was greater and of calcium, magnesium and chloride less and (c) retention of all minerals was greater, than on non‐laying days. The urinary findings can be largely explained in terms of the requirements of the shell gland for calcium and bicarbonate ions and the need to excrete the phosphate liberated from the skeleton during egg shell formation.