Horse metacarpal bone: age, ash content, cortical area and failure stress interrelationships.

In a study of interrelationships among the parameters of ash content, failure stress and cortical area of the horse metacarpal bone, bones from 41 horses aged 1 day to 33 years were analyzed. Calcium, phosphorus and magnesium in bone ash at all ages ranged from 35 to 39, 14 to 17 and .32 to .85%, respectively; range of calcium to phosphorus ratios was 2.1 to 2.6. There was no correlation between age and either percentage calcium or phosphorus in the ash or calcium to phosphorus ratio. Ash content of the bone reached a maximum at 4 years of age which was maintained through age 7 years, then declined. Area of the cortical portion of the bone increased sharply between 1 day and 1 year, from 4.6 + 1.2 to 6.7 + 2.4 cm2; highest values, averaging 8.8 + 1.5 cm 2, were found at 4 to 7 years of age. Failure stress values of the fresh bones increased sharply between 8 months and 1 year of age, with a maximum of 2328 kg/cm 2 reached at 4 to 7 years of age. A positive correlation was found between age and: ash content (r 2 = .57, P<.01); cortical area (r 2 = .63, P<.01); failure stress (r 2 = .51, P<.01). A lower positive correlation was found between failure stress and cortical area (r 2 = .40, P<.05), and a linear regression analysis of failure stress relative to ash content showed a positive correlation (r 2 = .58, P<.O1). Findings indicate that the metacarpal bone reaches maximum ash content, cortex area and failure stress resistance at age 4 to 7 years. (