It's generally not life- or career-threatening and is typically corrected with minor surgery.
"It's been a devastating thing, but we have to do what's right for the horse," said Mandella, who has never won the Derby with six previous starters. The trainer said Omaha Beach will have surgery in Kentucky in the next few days and will be sidelined for two to three weeks.
The ordeal will knock him off the Triple Crown trail.
"It's such a disappointment, but we'll fight again," Mandella told the AP. "We won't be out a long time."
The scratch was another blow to cancer survivor Rick Porter, the colt's 78-year-old owner.
Porter has twice finished second in the Derby, in 2007 with Hard Spun and the following year with filly Eight Belles, who broke her ankles past the finish line and had to be euthanised.
"He's a great sport," Mandella said. "I've got very good support."
Omaha Beach had been the 4-1 early favourite.
Mandella's dry sense of humour came out when he said, "My wife has my leg tied down so I can't jump out of the window."
Smith had chosen to ride Omaha Beach instead of Roadster and now he won't have a chance to win the Derby for the second straight year.
He rode Justify to victory last year.
"I'm a little bummed out, but the horse is okay and we're going to be all right," Smith said. "The good news is it wasn't anything that is life-threatening."
- AP
