CALCIUM AND PHOSPHORUS-METABOLISM IN GROWING PIGS .3. A MODEL RESOLUTION

The combined results of absorption and balance studies with kinetic studies on growing pigs were used to formulate and resolve a model of the metabolism of Ca and P and to evaluate the nutritional implications of increasing the intake of these minerals. Parameters of Ca and P absorption, excretion, bone accretion, bone resorption and intermediate mineral movements were calculated for a pig on either medium (8.4 and 7.7 g/d), or high (13.0 and 11.7 g/d) Ca and P intake. Utilization (balance/intake x 100) of Ca and P consumed in excess of the medium level was extremely poor (22 and 18%, respectively), compared to the utilization achieved at the medium level of intake (51 and 32%, respectively), which suggests that the pig's requirements have been met by the medium intake level. Bone accretion was not influenced by intake. However, bone resorption decreased by 63 and 47% from medium to high intake of Ca and P, respectively. These results and reports on persistent bone abnormalities in Danish pigs fed high levels of minerals indicate, that optimum mineral supply is not only a question of increasing mineral intake. The implication is rather that the pig's physiological regulation of bone growth and development is set at a different level than the corresponding regulation of muscle growth. Moreover, elevated level of mineral intake might impair normal bone development due to a decreased bone resorption.