A steeplechase horse is racing strongly, in contention to take the victory. But suddenly there’s a bobble after the final fence–a tendon is strained, and he pulls up lame. But almost immediately the horse’s body senses the injury and reacts, calling on its secret weapon–stem cells. Already the healing process is underway.

Stem cells are the primitive cells stored in various parts of the body, waiting to be sent out on missions to repair injuries. If a bone breaks or a ligament or tendon is strained or torn, signals are picked up by the stem cells and they travel to the site of injury–where they transform into whatever tissue is needed.

But today equine veterinarians have found a way to enhance this already impressive power: They’re harvesting stem cells to inject directly into an injured tendon.

Tendons and ligaments usually heal poorly because they have very little blood supply. So injecting a concentrated dose of cells directly into the injury promotes improved healing.

In early research it was thought that embryos were the only source of stem cells, but now we know that adult stem cells are located in many parts of the body, including bone marrow and fat tissue.

In this process, a small piece of fat is extracted from the fatty tissue next to the horse’s tail head, to obtain the necessary stem cells. The horse is under local anesthesia or anesthetized. With a cooperative horse, it takes about five minutes to harvest the 30 grams of fat that’s required.

If enough cells are injected into an injured tendon, they create elastic, normal tendon tissue during healing. The best results occur if this procedure takes place during the first month after the injury, while the body is still trying to regenerate new tissue and before scar tissue is formed. But chronic tendon lesions can benefit from these cells to help remodel scar tissue.

A Transformation

One stem cell success story is the 4-year-old Thoroughbred, Prospector’s Trick, owned by veterinarian Frederick Lewis and trained by Jeff Runco at Coleswood Farm near Charles Town, W.Va.

Jeff’s wife Susan has galloped horses for many years and handles race horse rehabilitation at their farm. She also shows hunters when time permits, although taking care of the mares and foals keeps her busy.

Prospector’s Trick had a promising future (one win and four seconds in six starts) but injured a tendon in his last race. Even with time off, the tendon hadn’t healed properly and each time they tried to bring the horse back into training the tendon would develop heat.

“It wouldn’t hold up when we started breezing him again. The tendon never looked terrible, but never really healed and had suspicious areas on ultrasound examinations,” said Susan.

After unsuccessful attempts to bring the horse back into training, Lewis decided to try stem cell therapy. Now, after several months of careful rehabilitation, Prospector’s Trick is sound and preparing to return to racing.

“I’m excited about it; the horse seems to be training out of it,” said Lewis. “He’s ready to run again and will have his first race very soon. He’s held up very well, so far. According to his trainers, it’s healing marvelously and he’s training well.”

Dr. Ian Harrison handled the procedure, which was done at Valley Equine Associates in Ranson, W. Va., adjacent to the Charles Town Racetrack.

Harrison works with race horses and performance horses, including Olympic-level three-day event horses and has done stem cell therapy on five patients. “Prospector’s Trick was the third one we did. He had a significant lesion in his superficial flexor tendon,” said Harrison. “He’d had the earlier injury, so it was a mixture of an acute injury and a chronic injury.”

The horse was brought to the clinic and a small sample of fat was harvested. It was shipped to VetStem, Inc., a lab in California, to concentrate the cells, and the concentrated stem cells were sent back in syringes, ready for injection. When the cells arrived, the horse returned to the clinic and the stem cells were injected directly into the injured tendon.

“Generally there’s about a three-day turnaround,” said Harrison. “We try to harvest the fat on a Monday, and the samples are back on Wednesday. We inject them that day, bandage the horse’s leg, and the horse goes back home.”

Harrison is amazed at the transformation. “On an ultrasound exam six weeks after we did the procedure, it basically looked like a normal tendon. We still have a long way to go [with stem cell therapy] to make sure a tendon has functional tissue that will stand up to the rigors of racing, but ultrasound showed there was certainly a tremendous improvement in this horse,” he said.

“If you’re using ultrasound as one of your criteria for watching a wound heal, there’s a dramatic improvement when using stem cells, compared with use of several other products,” Harrison added. “There are other products with similar sorts of claims. One of the old ones was Baptin, but horses treated with it tended to have a very high rate of breakdown injury.”

Harrison also noted there’s promising work being done now with A-cells used in conjunction with shock wave therapy. “[This therapy] seems to stimulate some very normal tendon repair, but my real interest in stem cell therapy is that it seems to be one of the few true physiologic treatments for the tendon,” said Harrison. “By putting cells in there that are going to produce normal tendon fibers, we help the horse create a strong structure again.”

On The Road To Recovery

After the injection, the horse begins a program of gradual rehabilitation.

“The protocol we’ve been using is a week in the stall, a couple of weeks of hand walking and then we ultrasound, to make sure there are no signs of any cellulitis or any other problem,” said Harrison. “The recovery, as evidenced by ultrasound, seems to be great. Several of these horses are back in training now, with no clinical signs of any tendon problem at the moment, so we are hoping that this kind of progress continues.”

It’s yet to be determined whether stem cell therapy can shorten the period of physical therapy. Many horses with a significantly injured superficial flexor tendon will take a minimum of four to six months to return to training. The stem cell therapy may not shorten that time period, but it certainly seems to aid normal healing, so the tendon can be strong again–without the scar tissue that puts it at risk for further injury and tearing.

The Runcos put Prospector’s Trick on a rehabilitation program immediately after the procedure. “The horse had already had three months off because of the injury, which was a year old. I walked him the very day of his stem cell injection, because I’d done a lot of reading about this and read the research articles,” said Susan.

Susan has a master’s degree in biology and understands the medical aspects of procedures used on their race horses. “I knew the importance of proper rehab. The veterinarian who came up with this procedure recommends immediate light use of the tendon, so the cells will line up properly as they heal.

Use of the tendon trains the stem cells to turn into the proper kind of tissue,” she explained.

The Runcos also used an Equicizer, which is similar to a hot-walker, with a central turnstile arrangement. Instead of being tied, however, the horses are free to move at will and are directed by gates that divide the round pen into sections.

Prospector’s Trick used the Equicizer 30 minutes a day for a month. Then he walked 40 minutes a day for another month. “I gave him two full months of walking before he started any faster work,” said Susan.

Prospector’s Trick then had two full months of jogging. “You can set the machine at various speeds. He was walking about 4 miles per hour, then jogging about 10 miles per hour. We had him jogging 2.5 miles per day after starting gradually–with shorter distances at first.

He had a full month of 2.5 miles per day before he went back to the track,” she said.

Susan noted that from a biological standpoint, stem cell therapy makes a lot of sense.

“It’s fairly non-invasive and innocuous because it uses the horse’s own stem cells. There’s no immunological issue [with cells coming from an outside source]. The risks are minimal; if you use sterile procedures there’s not much risk at all. The only setback is the expense. It costs about $2,500 to have this done. But if I had a horse I thought very much of, it would be worth doing, especially if it makes the difference in whether he becomes sound and able to compete,” she said.

Three of the horses that have undergone stem cell therapy at Valley Equine Associates are back in full training and doing well. “With more people doing this around the country, we’ll soon get a feel for whether this is normal tendon tissue, and whether we can alter the rehabilitation program. At this point that remains to be seen, but it certainly looks promising at the moment,” said Harrison.

“If you look at the extrapolations and use your imagination, you should theoretically be able to use stem cell therapy to help heal lots of things–such as fractured sesamoids or other problems,” said Harrison. “These cells become whatever they need to be. We could try putting them into the muscle or nerve supply of horses that have paralyzed larynxes, for instance. There are many things we might be able to fix with stem cells, besides putting them in a tendon. I think there will be a lot of work done on this in the near future.”

The Miracle Of Stem Cells

Vet-Stem, Inc., of San Diego, Calif., is the first company in the United States to offer stem cell harvesting. Robert Harman, DVM, and his co-founders had been involved in developing and testing human stem cell therapies since 1990, and formed their company in 2002 to work with equine veterinarians.
Cell biologists at the laboratory isolate and concentrate stem cells from fat tissue sent to them by veterinarians all over the country.

Some veterinarians use bone marrow or cultured bone marrow to treat tendon and suspensory ligament injuries inhorses, since bone marrow is a rich source of growth factor–which aids the healing process–as well as stem cells. But there’s a higher concentration of stem cells in fat tissue, and they’re easier to obtain.

“There are stem cells in muscle and other tissues, but fat is best for harvesting these cells because you can take out a little fat and the animal doesn’t miss it,” said Harman. There are few blood vessels or nerves in the pad of fat alongside the horse’s tail head so this is an easy place to collect the fat.

“The veterinarian makes an incision 2 inches long, goes in with a pair of surgical scissors and collects about 2 tablespoons of fat. He puts it into our special transport media and sends it to our lab via FedEx, on ice. It takes about six hours to process in the lab. If we get it by FedEx in the morning we can send it out again in the afternoon,” said Harman.

“We don’t culture these cells. Some people grow them into certain tissues [like cartilage] and implant that tissue in the injured site,” he explained. “But injured tissue is a very complex environment. The cells themselves are smarter than we are, in knowing what kind of tissue they should become. So we just put in these primitive cells, in their natural state. The local damage tells them what to do. If we put them in a tendon, they make new tendon. If we put them in a fracture they turn into osteoblasts and make bone. If you inject them into a heart, they make new heart muscle.”

Under natural conditions in the body, stem cells are waiting in the fat and are attracted to wherever there’s injury or inflammation.

“You can put them into the blood intravenously and they go wherever they’re needed,” he said. “This is how Mother Nature heals injured tissues. If a body suffers injury, signals go out through the bloodstream, the cells ‘hear’ that signal, and come. It’s a numbers game, however. The reason not enough of them get attracted to a tendon or ligament is that these tissues don’t have a very good blood supply. So injecting these cells directly into the tendon can aid healing.”

At this point in time, most horses being treated with stem cell therapy are high level performance horses in which proper healing, with no scarring, is important–so they can regain full use and soundness for peak competition levels.