Limited nutritional energy supply differentially impairs growth and bone mineralization of the developing lumbar vertebrae in minipigs

Bone development during puberty and adolescence may influence the later risk of osteoporosis. The aim of this study was to investigate whether the three-dimensional development of the lumbar vertebrae is impaired in terms of bone mineral density and temporal control during the pubertal growth spurt when caloric intake is limited. Two groups of prepubertal female Gottingen minipigs (each n = 6) were fed either ad libitum (free fed) or with reduced food intake (controlled fed) for 12 months using a standard diet. Apparent volumetric bone mineral densities (vBMD) and size of the 4th vertebra were measured by quantitative CT in monthly intervals. The weight of free-fed animals was 29.5 +/- 0.9 kg compared to 25.9 +/- 3.5 kg in the controlled-fed group at the end of the observation period (mean +/- SD; p < 0.05). The maximal cross-sectional area of the 4th vertebra was 148.2 +/- 3.4 mm(2) in free-fed animals compared to 143.1 +/- 6.3 mm(2) in controlled-fed animals (P < 0.05) as both, the cortical and the medullary area were greater in the free-fed group. In contrast, cancellous and cortical bone mineral densities were not different between the two groups; however, maximal densities were reached earlier in the free-fed group. As regards the height of the vertebra, no difference was observed between the groups after 12 months (25.46 +/- 0.54 mm in controlled fed vs. 25.56 +/- 0.45 mm in free fed), although the peak height was reached earlier in the free-fed group. In both groups, the maximal growth rate in the cross-sectional direction was reached earlier compared to the longitudinal direction (both P < 0.05). Growth in the longitudinal direction that occurs in the primary and secondary epiphysis does not appear to depend on caloric intake contrary to the periosteal and endocortical bone generation in the cross-sectional direction. When limited energy is available, the organism seems to preserve the development of normal body height, while accepting reduced strength of the vertebra.