LOUISVILLE, Ky. -- Uncle Mo won't run in Saturday's Kentucky Derby because of a puzzling internal ailment that has reduced his appetite and energy. The loss of the biggest name in a field already short on star power makes the race even more wide open.
Owner Mike Repole announced the decision to scratch the colt Friday morning, about 40 minutes before Derby wagering opened. Uncle Mo was the 9-2 second choice on the morning line.
His absence reduces the field for the Derby to 19 horses. Dialed In is the 4-1 early favorite. Churchill Downs oddsmaker Mike Battaglia was expected to revise the morning line later Friday.
In 2009, favorite I Want Revenge was scratched on the morning of the Derby with a career-ending leg injury. A week before last year's Derby, heavy favorite Eskendereya dropped out with a bad ankle.
"It shows how tough our business is and how unfortunate it is, too," said Dialed In trainer Nick Zito, superstitiously knocking on a wood sign on his barn. "We all would have liked to see him run. It's devastating."
The Derby dreams of Repole and trainer Todd Pletcher aren't completely dashed. Repole owns and Pletcher trains 20-1 shot Stay Thirsty, but their biggest hopes rested with Uncle Mo.
"Uncle Mo is a franchise player," Pletcher said. "Our confidence level with a healthy Uncle Mo would have been pretty high."
Repole has 100 family and friends in town for the race.
"He had tremendous pressure on him," said Robert LaPenta, owner of Dialed In. "He's not only feeling bad for himself, he's feeling bad for all of the people who had such high hopes."
Jockey John Velazquez, who is 0 for 12 in the Derby, lost his mount on Uncle Mo. He was then named to ride Animal Kingdom, replacing Robby Albarado, who broke his nose in a spill earlier this week. Ramon Dominguez will be aboard Stay Thirsty.
Hall of Fame trainer Bob Baffert empathized with Pletcher, having lost two of his other Derby contenders, The Factor and Jaycito, on the road to the Derby.
"You're never safe until you put that saddle on because anything can happen," said Baffert, who will saddle Midnight Interlude. "Everybody says there's no woofing in your sport. That's because we don't want to jinx ourselves. You woof afterwards, when you win."
Pletcher, who trained Eskendereya, still won his first Derby last year with long shot Super Saver.
"Honestly, I've never had a horse as good as Uncle Mo," he said. "To not make it here is a big letdown. I take it as a personal failure."
Uncle Mo's illness, which began as a gastrointestinal inflammation, was discovered after he was upset as the heavy favorite in the Wood Memorial on April 9. He led most of the way before finishing third, beaten by a length.
The colt was put on medication, which Pletcher said helped initially, and he continued training in preparation for the 1 1/4-mile Derby, the opening leg of the Triple Crown series.
On the track during workouts, Uncle Mo appeared to be in good form, and Repole said the colt was 100 percent sound. He "galloped like a monster" Friday morning, Pletcher added.
Around the barn, though, he was showing signs that something was amiss. His appetite was lower, he lost weight and his coat didn't look good, Pletcher said.
"We've got something going on inside that I don't know what it is. The best vets in the world don't know what it is," the trainer said. "When you don't know, that's when I get scared."
Three vets examined Uncle Mo on Thursday and didn't say the colt couldn't run in the Derby. However, after they left the barn, Pletcher sat down with Repole and said he didn't want Uncle Mo to go.
"I'm actually relieved and now I'm really concerned and worried about Uncle Mo," Repole said. "We've gotten the best vets. I'm willing to give this horse the best resources to come back. He is a superstar."
Pletcher said Uncle Mo had a GI infection, but no one is sure if it was the main issue or a secondary problem. The colt's blood work showed a specific enzyme was elevated, and the vets couldn't explain why.
"They're baffled," Repole said. "That's what gets us nervous the most."
For now, Uncle Mo will remain at Churchill Downs and may visit a clinic for another diagnosis.
Pletcher decided Thursday that Uncle Mo shouldn't run and Repole agreed. Both defended the decision to enter the horse on Wednesday, which ensured that Sway Away would be excluded from the field, limited to 20 starters.
"We weren't trying to prevent someone else from entering. We needed every minute to try to figure this out and we ran out of time," Pletcher said.