The effects of different exercise conditions on metacarpal bone strains in Thoroughbred racehorses

Excessive strains are thought to cause dorsal metacarpal disease (shin-soreness) in young Thoroughbred racehorses. Strains were measured on the dorsal cortex of the third metacarpal bones in 6 yearling (16 to 19 months old) and 6 adult (4 to 8 years old) Thoroughbred horses during exercise on a treadmill and on different track surfaces (sand, grass, woodchip, bitumen and dirt). Strains were always higher on the outside limb than the inside limb during turns. Strains were higher in the non-lead limb than the lead limb in canter and gallop. Strains increased with fatigue. Changing the track surface, inclining the treadmill to 5.2 degrees and changing the angle of the ground reaction force by changing hoof balance did not increase strains. These findings suggest that track shape will directly affect the incidence of shin soreness, while track surface and camber will not have a direct effect.