PSI-1 - Depletion and Repletion Dynamics of Individual and Regional Bone-mineral Reserves in Replacement Gilts Fed Different Levels of Dietary Phosphorus and Calcium

Abstract: The aim of this study was to evaluate the ability of replacement gilts to compensate (repletion), before their insemination, bone-mineralization deficit in individual bones or bone regions that resulted from low dietary phosphorus (P) and calcium (Ca) supply during the growing period (depletion). A total of 24 gilts were fed according to a two-phase feeding program (60-95 and 95-140 kg BW, respectively). During the depletion period, the gilts were fed ad libitum a finisher diet providing either 100% or 60% of the estimated P requirement (D100 with 2.1 g and D60 with 1.2 g digestible P/kg, respectively). During the repletion period, half of the gilts from each finisher diet were randomly assigned to either a restrictively fed control or a high-P diet (R100 with 2.1 g and R160 with 3.5 g digestible P/kg, respectively) according to a 2 × 2 factorial design, resulting in four treatments: D60-R100, D60-R160, D100-R100 and D100-R160. Bone mineral content (BMC) in the entire body, individual bones (femur and spine lumbar L2-L4), and bone regions (front legs and hind legs) were measured in each gilt at two-week intervals using dual-energy X-ray absorptiometry (DXA). At 95 kg, gilts fed D60 had lower BMC in the entire body, all individual bones and bone regions than those fed D100 (P< 0.001). The spine lumbar L2-L4 lost more BMC (-17%; P< 0.001) than the other sites, which decreased by 7% in the hind legs (P=0.001), 9% in the femur (P=0.002) and 10% in the head and trunk (P=0.043 and P=0.006). At 140 kg, all sites studied had similar BMC. In D60 gilts, recovery was reached 2 (P< 0.001) and 4 weeks (P< 0.001) after the depletion period when fed the R160 and R100 diets, respectively. These results show that replacement gilts can regain mineral deficits in all individual bones and bone regions.