Bone development is more rapid in younger animals but declines as the animal reaches market weight. Because of this, a higher die-tary concentration of calcium and phosphorus is required for starter and grower than for finisher pigs. Although the rate of bone formation declines as the animal enters the latter stages of growth, the skeleton is still growing albeit at a slower rate. During the latter growth period, bones widen and become thicker and thus stronger. Finisher pigs therefore have the capacity to deposit calcium and phosphorus in their bone tissue beyond that needed to attain optimum growth responses. The need for the higher deposition of minerals in bone is not necessary for pigs destined for market, whereas gilts that are being retained for the breeding herd need to store additional minerals which can serve as reserves for later reproduction. Consequently, replacement gilts fed a finisher diet containing lower calcium and phosphorus concentrations will likely develop a weaker skeletal structure. Increasing the dietary calcium and phosphorus by 0.10% above that recommended for market swine will result in optimum bone mineralization in replacement animals.