Recovery of bone strength in young pigs from an induced short-term dietary calcium deficit followed by a calcium replete diet.

This study investigated whether the deficits in bone strength of pre-pubertal pigs, induced by short-term deficits in dietary calcium can be recovered if followed by a calcium-fortified diet. Young pigs were divided into two groups based on diet: a marginal Ca diet (70% of established Ca requirements) or an excess Ca diet (150% of established Ca requirements) for 4 weeks. Each group was then randomly sub-divided into two groups and fed diets with either marginal or excess dietary Ca for 6 weeks in a cross-over design, resulting in four treatment groups: H150-H150, H150-L70, L70-H150, and L70-L70. Animals were DXA scanned at 2-week intervals during the 10-week period to obtain whole body bone mineral content (BMC) and density (BMD). After animals were euthanized, right femurs were collected for this study. Traits such as bone mineral density, mass, volume, area moment of inertia (MI) and the section modulus (SM) were computed from computed tomography (CT) data and failure load was measured from four-point bending tests. DXA results showed significant reduction in BMC (61.6%) and BMD (37.5%) in the (L70-L70) group compared to the (H150-H150) group. DXA results additionally showed that deficiencies induced by the 4-week marginal Ca diet in the (L70-H150) group were not recovered with a subsequent excess Ca diet. While mechanical test results also showed significant reduction (75%) in strength in the L70-L70 group, compared to the H150-H150 group, they revealed no differences between the failure loads of the (L70-H150) group and the (H150-H150) group. Similar results were also found for bone mineral mass and volume, indicating that recovery from a short-term dietary Ca deficiency is possible at the pre-pubertal stage. Furthermore, bone mineral content and bone volume calculated from CT data correlated highly with failure load (R(2)=0.78 and 0.84, respectively), while density, MI and SM only showed weak-to-moderate correlations (R(2)=0.40-0.56), implying that bone mineral mass and volume calculated from CT data are good non-invasive surrogates for strength of growing bones.