Paul Jaynes, a retiree living in Florida, was heartbroken when his 9-year-old Labrador, Cookie, suddenly stopped walking last year. The once-athletic dog struggled to stand and, if she moved at all, collapsed after a few steps.

He carried his 90-pound companion to his truck, drove her to the vet and braced himself. Surely she couldn’t live like this.

Instead of giving him bad news, Jaynes’s veterinarian told him about a newly available procedure involving stem cells. In a single day, the vet said, his office could remove cells from Cookie’s fatty tissues, process them and re-inject them into her joints. She could go home immediately.

“It was very dramatic,” Jaynes says. “The day after surgery, she was standing. . . . Within a week, she was almost back to her old self.”

Six months later, Cookie is still going strong, Jaynes says. While he has no doubts about the treatment, some veterinarians worry that marketing of stem-cell therapy for animals has gotten ahead of the research needed to validate its use.

“Most of what you hear is anecdotal — ‘Oh, I tried this, and it helped my dog,’ ” says Jeffrey Peck, a veterinary surgeon in Mait­land, Fla. “This has grown in its marketing exponentially greater than it has grown in evidence.”

Much of his practice is in orthopedics — typically, dogs with hip dysplasia or arthritis. He tried stem-cell therapy in 2008 but dropped it after a dozen cases in which he saw no improvement.

“I don’t refuse to do it if a client really wants to try, but I give them my disclaimer,” he says. At $1,400 to $3,000 for the procedure, most pet owners opt out, he says.

Some of Peck’s colleagues are decidedly more optimistic about the therapy.

Janis Fullenwider, owner of a Florida animal hospital, began offering the treatment about a year ago, and has treated only five dogs so far.

“I think it will turn out to be extremely promising — not just for osteoarthritis but for all kinds of things,” she says.

Her enthusiasm comes despite an early — and profound — disappointment. Four years ago, one of her dogs was a subject in a pilot study to test stem-cell therapy for cardiomyopathy in Dobermans, half of which eventually develop the fatal heart-muscle disease. Fullenwider’s dog died the day after the treatment.

Although the dog might have died that day in any event, researchers said the stem cells showed no sign of helping.

Research on stem cells for pets is growing. The University of Florida, for instance, is conducting a study involving dogs with arthritic elbows (the middle joint of the front legs).

Fourteen have completed the six-month trial, during which the owners, other veterinarians and technicians are kept in the dark about which dogs are getting the therapy and which are getting a placebo. The placebo dogs get the treatment at the end.

“I think for this application — for arthritis — it’s very useful, says Anna Dunlap, a veterinarian and orthopedic fellow working on the study. “The owners tend to guess correctly. They’ll come in at three months and say, ‘I think my dog is in the stem-cell group because he’s really improving’ — and they’re usually right.”

Her research uses stem cells from canine umbilical cords harvested during Caesarean-section births. The more common practice is to remove them from fatty tissue — either behind the dog’s neck or on its abdomen — then process the cells and inject them into the troublesome site. Although adverse effects are rare, the procedure does bring a risk of joint infection.

— Fort Lauderdale Sun Sentinel