KENNETT SQUARE, Pa. (AP) – Doctors were “pulling out all the stops” to save Kentucky Derby winner Barbaro, who suffered a significant setback in his recovery from laminitis after months of upbeat reports.

Chief surgeon Dean Richardson removed damaged tissue from Barbaro’s left hind hoof, and co-owner Gretchen Jackson said Wednesday that the colt was lightly sedated and back in a protective sling in his ICU stall at the University of Pennsylvania’s New Bolton Center.

“They’re taking extreme measures,” Jackson said. “They’re treating it very aggressively. They’re really pulling out all the stops to help him.”

Jackson said she brought Barbaro grass on Wednesday morning and said the colt’s appearance was “not as bright.” But she added her husband, Roy, visited Barbaro later in the day and his appearance had visibly improved.

Barbaro was being treated aggressively for his discomfort and is in stable condition, according to a statement released Wednesday morning by the Center. The tissue was removed Tuesday night.

“Things were marching along pretty smoothly until this,” Jackson said. “We’ve been there before with him. He’s a horse that wants to live.”

Barbaro had become uncomfortable with his left hind foot, and a cast was removed after some new separation on the inside portion of his hoof was found. The cast had been on a week to help realign a bone.

The cast change could have caused some inflammation, said Dr. Kathleen Anderson, Barbaro’s attending vet when the horse was racing and stabled in trainer Michael Matz’s barn at the Fair Hill Training Center in Elkton, Md.

Anderson said Barbaro has proved he was strong enough to overcome his latest medical obstacle.

“We all know most horses don’t get this far,” she said. “The bottom line with Barbaro is the fractured leg is the one that would have been the end of most horses. He won’t be getting to the big green field any time soon, but I don’t think this is insurmountable.”

It was the first bad news after months of progress. The owners and Richardson even talked about releasing Barbaro from the hospital, perhaps by the end of the month.

“It’s sad that’s he’s had a setback because he was marching along toward living outside the hospital,” Jackson said. “The only thing we care about is that he’s not in pain.”

Barbaro shattered his right hind leg in the Preakness on May 20. In mid-July severe laminitis, a potentially fatal disease caused by uneven weight distribution in the limbs, resulted in 80 percent of Barbaro’s left hind hoof being removed.

“I was there yesterday and it was obvious he was not comfortable in that foot,” Jackson said. “The easiest and best way to work on Barbaro is when he’s laying down. They had to wait until he was laying down and when they removed the cast, they discovered some reason for him feeling pain.”

Just over a week ago, Richardson said Barbaro’s right hind was getting stronger and should eventually be healthy enough to allow the colt to live a comfortable, happy life.

But he also warned: “Barbaro’s left hind foot, which had laminitis, remains a more formidable long-term challenge. The foot must grow much more for him to have a truly successful outcome.”

The disease, called laminitis or founder, involves inflammation and structural damage to tissue that bonds the horse’s bone to the inner wall of the hoof. Richardson said in July that Barbaro’s laminitis was “basically as bad a laminitis as you can have. It’s as bad as it gets.”