Calcium and phosphorus metabolism in broilers: Effect of homeostatic mechanism on calcium and phosphorus digestibility1

SUMMARY In this paper, we present a review of the current knowledge of calcium and phosphorus metabolism as it relates to homeostatic mechanisms in poultry; contrasts with mammalian systems, as well as information that is available for mammalian systems but not for avian systems, are included. The importance of understanding these homeostatic mechanisms and their effect on Ca and P absorption are discussed briefly in the context of correctly formulating poultry diets. Clearly deficiencies, excesses, or imbalances in Ca and P result in a cascade of changes, including increases or decreases in the absorption of these 2 minerals from the intestinal lumen. The effect of these changes on the actual digestibility of Ca and P from ingredients or diets has not been determined yet; most of the methodologies we used for the determination of P digestibility are done under deficient conditions. The methods used to determine the release of Ca and P from diets when phytases were used were also done under deficient Ca and P conditions. given the effect of Ca and P homeostatic mechanisms on absorption, methodologies and, possibly, the quantitative the effect of these homeostatic mechanisms on values generated for Ca and P should be reviewed before they can confidently be applied.