When Pete Giangiulio heard the news about Barbaro yesterday, he thought of the autistic foal on his Unionville farm who walks in tiny circles all day and will feed only at 11 p.m.

"She'll never race. She'll never breed. But we keep her world small," said Giangiulio, who owns Castle Rock Farm. "She's happy. She has a quality of life.

"I'm sure Barbaro lived in a happy little world this last year," he said. "But when the Jacksons [owners Roy and Gretchen] saw that it was no longer possible for him to be happy in it, they made the decision they had to make. It's emotional and it's very difficult, but it's the right decision."

What often makes that moment so difficult, racehorse owners said yesterday, is the emotional attachment that develops between the athletic animals and the humans who train and care for them.

"You feel the same way you would if you lost a loved one," said Stuart Janney III, a Maryland breeder whose parents owned Ruffian, the great filly who was euthanized after fracturing a leg in a 1975 match race at Belmont Park.

Patricia Chapman, who with her late husband, Roy, owned 2004 Kentucky Derby winner Smarty Jones, said she's often been asked why humans and the racehorses they own grow so close.

"I've never had a good answer," she said from her home in Boca Grande, Fla. "But when you watch them race, you just know that they're trying with their whole heart for you. They ask for so little in return. They're just special creatures who are gifts from God."

Not everyone believes there is a divine element to that horse-human connection. Some owners compare the relationship to that between members of an athletic team. Others see a kind of minor-league version of the parent-child dynamic at work; "a maternal/paternal thing" was how Giangiulio described it.

Like children, horses need help to survive, require constant supervision, and do best when they've been treated with the right mix of love and discipline.

"We've domesticated these animals to the point where they can no longer care for themselves, so we have a responsibility to them," said Rick Abbott, who operates the Charlton breeding farm in Cochranville. "We raise them, and they look to us for their care and well-being. That's how the bond forms."

All agreed that once it becomes clear that a horse has little to look forward to but suffering, the decision to end its life, while never easy, is typically an obvious one.

"At a certain point, it becomes pretty cut and dried," Abbott said. "No matter how much you want to save the horse, you understand that it's just not going to work. That's why I hate to see people put their dogs through chemotherapy and all these unspeakable things. But they do it because they just don't want to make that difficult decision."

Art Zubrod, who breeds standardbred racehorses on his Versailles, Ky., farm, has been there. Last fall, at the University of Pennsylvania's New Bolton Center, he had to put down his best horse. Artsplace, who had won more than $3 million, was harness racing's horse of the year in 1992 and had become an extremely successful sire.

But as he aged, Artsplace developed laminitis, the same disease that contributed to Barbaro's demise. He would improve for days at a time and then slip backward. In the week before the horse was put down, Zubrod and the veterinarian talked several times a day.

"I can remember being on the phone with him near the end," Zubrod said. "Both of us were choking up simultaneously, thinking about what was to come. But when that time came [to put him down], we knew that as long as we had the best interest of the horse at heart, there was no other decision we could make."

While it's the owners who, with the vet, ultimately determine an ailing horse's fate, the decision impacts all those who have worked with the animal.

"There's grooms, exercise boys, jockeys, trainers as well as owners," Giangiulio said. "They're all invested."

In the end, though, the need to conclude an ailing animal's life is frequently a routine part of the horse world.

"I'm no horse hugger," Giangiulio said, "but the life of a horse is no less important to that horse than the life of a human is to a human. As hard as it is for them now, the Jacksons have had this happen before, and they'll have it happen again. They understand that you can't keep them alive for you."

Contact staff writer Frank Fitzpatrick at 215-854-5068 or ffitzpatrick@phillynews.com.