Terrain, who pulled up in Friday's Iowa Derby, came out of the race with broken sesamoid bones in his right front ankle and had to be euthanized.

Trainer Al Stall said that the bones were shattered so severely that Terrain could not be saved. The gelding also had a condylar fracture in the cannon bone of his leg.

Terrain, the even-money favorite in the $250,000 race, was pulled up approaching the far turn after jockey Robby Albarado felt him take an awkward step.

"Robby said he felt something on the backside and tried to wrap up on him right away," Stall said. "... If you could freeze frame and stop him right then, he might have been all right, but he had adrenaline and he was a fighting type of horse."

Terrain was known as a small gelding who outran his size. He had won three of nine starts and $512,084 in a career marked by game efforts against the nation's best horses.

He was second in the Breeders' Futurity and fourth in the Breeders' Cup Juvenile last year and had been third in the Louisiana Derby, fourth in the Blue Grass Stakes and seventh in the Preakness Stakes this year.

Stall said that Terrain was his second horse to suffer a fatal breakdown in 19 years of training.

"It takes your confidence away from you," Stall said. "You think, 'What's next?' "