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

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 2-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, one-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 4 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 2-week intervals using dual-energy X-ray absorptiometry (DXA). At 95 kg, gilts fed D60 had less 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.