Can race horses break down

Just as the starting bell sounded and the race began, Ruffian hit her shoulder extremely hard on the starting gate. She recovered quickly, but was obviously in pain and leaning more heavily on her right foreleg compensating for the pain. The first quarter-mile (402 m) was run in a blazing 22 1/5 seconds, with Ruffian ahead by a nose. Little more than a 1 furlong (201 m) later, Ruffian was in front by half a length when both sesamoid bones in her right foreleg snapped. Vasquez tried to pull her up, but the filly wouldn't stop. She kept on running, pulverizing her sesamoids, ripping the skin of her fetlock as the bones burst through, driving the open wound into the sting sand of the Belmont track, tearing her ligaments, until her hoof was flopping uselessly, bent up like the tip of a ski. She was known for her incredible love of running and unwillingness to lose. She had never before been behind in a race. http://en.wikipedia.org/wiki/Ruffian_(horse) http://www.YouTube.com/watch?v=fsi_ixx4pAY