Calcium and Phosphorus Interrelationships in the Intestine of the Fowl

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Abstract
The solubility and interrelationships of intestinal calcium and phosphate were investigated in two trials involving chicks and in one involving laying hens. Dietary calcium was the variable in one chick and one hen trial while dietary phosphate was the variable in the second chick trial. Analyses were performed on ultrafiltrates as well as total contents taken from four intestinal segments and stomach output material. The concentration of ultrafilterable calcium decreased with the distance from the pylorus while total calcium increased, in most cases. A similar trend existed also for phosphate, except that an increase was noted between the stomach output and the duodenal contents. Concentration of ultrafilterable calcium increased with concentration of total calcium, at all levels of the intestine. The rate of this increase was lower in the posterior as compared to the anterior segments. Regression of intestinal calcium on phosphate in chicks was positive with a slope of about 2 at all levels of the intestine. This constant relationship suggested precipitation of a rather defined mineral in the intestine. With laying bens the function of phosphate on calcium could be described exponentially with phosphate concentration approaching an asymptotic value. The implications of these results with regard to calcium and phosphate absorption are discussed.