Observations on the mineral metabolism of pullets. V: Acid-base equilibrium and reproductive activity

Abstract

1. Calcium and phosphorus balance experiments with pullets during which the plasma alkali reserve of the birds was followed are described. Evidence is produced in support of the view that the onset of reproductive activity in the pullet is accompanied by an increase in plasma alkali reserve, as well as of calcium retention, provided the ration contains adequate calcium carbonate.2. These high levels of plasma alkali reserve tend to decrease with the beginning of laying, but apparently the plasma alkali reserve of laying birds tends in general to remain higher than that of the non-laying bird or of cocks.3. The possible bearing of these observations on bone mineral composition and Ca/P retention ratios is discussed.4. It is shown that on a cereal ration moderately low in calcium, where the apparent digestibility, of phytic acid phosphorus is of the order of 40–70%, it was not possible to correlate apparent digestibility with the calcium metabolism of shell formation. When the same ration was supplemented with 5% calcium carbonate, so that the apparent digestibility was of the order of 9–25%, then it was possible under circumstances of intense laying to detect a slight increase of apparent digestibility in association with laying.