Concussive laminitis (road founder), Concussive Soring Practices: When horses are subjected to excessive, fast, or
prolonged work on hard surfaces they may develop laminitis as a result of
trauma to the laminae, particularly if their horn quality is poor.
Road founder is considered a "mechanical" means of obtaining high front end action. It causes the horses to lift (snatch) their legs higher (away from pain).
An excerpt from an article by James Rooney, DVM:
Road founder is tearing of the tissues between the distal phalanx and the
hoof wall. The lesion is most severe and obvious
at the apex of the third phalanx, extending a variable distance toward the
quarters. Histologically, there is disruption and tearing of collagen fibers
with hemorrhage and edema. With time the damaged area is filled with
granulation and, eventually, scar tissue.
In the old literature this was described in carriage horses, animals with
heavy bodies, relatively light legs, and long toes for flashy, high
"action." These animals characteristically moved at speed on hard surfaces,
for considerable distances, and pulling considerable loads. This combination
of conditions is not often met with in modern times, but road founder does
occur in heavier horses with long toes.
The clinical signs with road founder can vary from slight to severe lameness
of one or both front feet and in the acute stage are not readily
differentiated from classical laminitis. The subsequent clinical course is
less catastrophic, of course.
"It ain't 'unting on the 'ill wot 'urts the 'orses 'oof, its 'ammer, 'ammer, 'ammer on the 'ard 'igh road."
Translation: It ain't hunting on the hill that hurts the horse's hoof, it's hammer, hammer, hammer on the hard high road.