Osteoinductive response in the dorsal aspect of the carpus of young thoroughbreds in training occurs within months.

Bone mineral density (BMD) was measured by dual x-ray absorptiometry (DXA) in the carpus of 6 Thoroughbreds age 24 months that were exercised on the treadmill for 4.5 months, and of 6 matched control horses. A sagittal slab of known thickness was sawn from one or more of radius, radial carpal (Cr), third carpal (C3), and third metacarpal (Mc3) bones. After the 4.5 month treadmill exercise, there was a significantly greater volumetric BMD in the dorsal aspect of C3 (P = 0.006). Treadmill-exercised horses also had higher BMD in the dorsodistal aspect of the radius (P = 0.03), the dorsal half of Mc3 (P = 0.012), and the dorsal aspect of Cr (P = 0.04). In other areas of interest (AOI) studied on the palmar aspect of the bones, significant increases in exercised horses did not occur. These sizeable changes in bone mass occurred within a few months of initiation of exercise. With technical development, DXA could be applied in vivo for investigation of changes in bone mass of horses which are growing and exercising under various regimes. The data are also relevant to the development of scientifically based training protocols.