Utilization of Calcium and Phosphorus from Hydrous and Anhydrous Dicalcium Phosphates

Abstract

Studies were conducted with chickens and turkeys to determine factors which affect the nutritional availability of phosphorus from dicalcium phosphates. Incorporation of orally administered 45Ca and 32P from either 45CaH32PO4 or 45CaH32PO4·2H2O into bone was 25 to 50% greater from the hydrous form than from the anhydrous form in 1-week-old birds. For chickens the differences in incorporation of 45Ca and 32P from anhydrous and hydrous dicalcium phosphate decreased gradually, so that at 5 weeks of age, equal amounts of 45Ca and 32P were incorporated into the femur when chicks were fed either form of the phosphate. In turkeys, the incorporation of 45Ca and 32P was greater when supplied in the hydrous form than in the anhydrous form throughout the 5-week experimental period. Further studies were conducted with 1-week-old chicks and turkeys fed controlled amounts of feed and killed at 1, 2 and 4 hours after oral dosing. Incorporation of 45Ca and 32P into the femur from anhydrous dicalcium phosphate was again less at each time interval than incorporation from hydrous dicalcium phosphate. Measurement of the rate of solution for CaHPO4·2H2O at pH 3 to 7 indicated that the differences in incorporation may be due in part to differences in solution rates. The solution rate and the amounts of 45Ca and 32P incorporated into the bone were both higher with hydrous dicalcium phosphate.