Influence of exercise on bone mineral density of immature cortical and trabecular bone of the equine metacarpus and proximal sesamoid bone

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Abstract
Bone mineral density (BMD) and cross-sectional area (CSA), measured using peripheral quantitative computed tomography, were determined in the left third metacarpal bone (MCIII) and left medial proximal sesamoid bone (psb) in 3 differently exercised groups of foals. Group(box) (n = 14) was confined to a box stall from birth to age 5 months, Group(training) (n = 14) was kept in similar box stalls but additionally given a daily exercise programme consisting of an increasing number of gallop sprints and Group(pasture) (n = 15) remained at pasture. At 5 months of age, 8 foals from each group were randomly selected and subjected to euthanasia, the remaining 19 foals were given an identical light exercise regimen for an additional 6 months and were killed at age 11 months. In MCIII CSA increased with age and was also significantly (P<0.05) larger in Group(pasture) compared to Group(box) at age 5 months. At 11 months this difference had disappeared. In the dorsal cortex, BMD was significantly (P<0.05) higher in Group(box) than in both other groups. At age 11 months all significant differences had disappeared. In the psb, CSA increased with age, but there were no differences between the exercise groups. At the apical level, trabecular BMD was higher in Group(training) than in Group(box) and Group(pasture) (P<0.001 and P<0.01, respectively). At 11 months, trabecular BMD in the foals that had belonged to Group(training) was less than in the foals that had belonged to Group(box) (P<0.05). It is concluded that box-rest during the first months of life results in a retardation of normal development which is compensated for when the restriction on exercise is lifted. Exercise during the first months of life induces an increase in CSA in the third metacarpal bone. In the psb exercise increases BMD, principally in trabecular bone. There is an indication that the specific training regimen used in this study led to an overstimulation of the bone resulting in less active mineral deposition in the longer term.