You've seen poster children for the Shriner's Children's Hospitals. Often these depict a child with orthopedic problems. Foals often have orthopedic problems, too. Problems classified as DOD include physitis, angular leg deformities, flexure leg deformities, osteochondritis dessecans and the wobbler syndrome. All relate to disturbances in the normal growth of bone.
Some cases occur without any outward signs.
Foals may get better with no or little effect on their future usefulness. These injuries may not be noticeable until there's an enlargement of a joint or lameness. Lame foals are commonly stalled with their dams. Stall rest results in less stress, so the new bone is weaker than that under pasture conditions. When turned out a few days later, the foal runs and plays, crushing the newly laid-down, but weaker, bone.