Quarter Crack - The Hoof Mechanism

The Hoof Mechanism

The horse hoof is not at all a rigid structure. It is elastic and flexible. Just squeezing the heels by hand will demonstrate that. When loaded, the hoof physiologically changes its shape. In part, this is a result of solar concavity, which has a variable depth, in the region of 1–1.5 cm. In part, it is a result of the arched shape of the lateral lower profile of the walls and sole, so that when an unloaded hoof touches a firm ground surface, there is only contact at toe and heels (active contact). A loaded hoof has a much greater area of ground contact (passive contact), covering the lower wall edge, most of the sole, bars and frog. Active contact areas can be seen as slightly protruding spots in the walls and in the callused sole.

The shape changes in a loaded hoof are complex. The plantar arch flattens, the solar concavity decreases in depth and heels spread. The hoof diameter increases to a 'dilated' configuration and P3 drops marginally into the hoof capsule. There is some recent evidence that a depression takes place in this phase, with blood pooling ('diastolic phase') mainly into the wall corium. When unloaded, the hoof restores its 'contracted' configuration, the pressure rises and the blood is squeezed out ('systolic phase'). There is a secondary pumping action, with the flexion of the foot, as it is raised.

The hoof mechanism ensures an effective blood circulation into the hoof, and it aids general circulation, too.