For thoroughbreds in this U.S. Caribbean territory, being fast enough to win, place or show is a matter of life and death _ losers often don't even make it off the racetrack grounds alive.

More than 400 horses, many in perfect health, are killed each year by injection at a clinic behind the Hipodromo Camarero racetrack, said chief veterinarian Jose Garcia. The Associated Press on Friday examined clinic log books that confirmed Garcia's account.

The handwritten logs list the names of the horses, the trainers, the date of execution and the dosages of lethal drugs. Garcia allowed an AP reporter to view the logs but prohibited him from taking notes or photographing the pages.

Unlike on the U.S. mainland, where many former racehorses are retrained for riding or sent to refuges, the animals have few options in Puerto Rico. Owners say caring for and feeding a losing racehorse is too expensive.

"If it doesn't produce, after a while I give it away or I kill it," said Arnoldo Maldonado, 60, a businessman who races about five horses a year. "It bothers me, but it has to be done because there is no money to pay for them. ... I'm not going to keep losing."

The killings also bother veterinarians who carry them out.

While many horses are unsuitable for adoption because of injuries or bad tempers, far more could be rescued than the current few dozen a year, Garcia said.

The veterinarians at the racetrack clinic have an informal system of contacting farms and breeders about a possible home for the animal when a healthy horse comes in to die. But so far there are no programs such as the U.S.-based Thoroughbred Retirement Foundation, which rescues horses coming off the track.

The racehorses put to death in Puerto Rico are not being killed because they have suffered a serious injury, like Eight Belles, the filly euthanized after breaking both front ankles in the Kentucky Derby on May 3. Here, even when a second home is available, veterinarians say that some owners want losing horses executed anyway _ some to save money, others for revenge.

"You'll get a few owners who get so upset, they just want the horse dead," said veterinarian Shakyra Rosario.

She often asks trainers if they have extra space so she doesn't have to kill a healthy horse, and there are Puerto Ricans such as trainer Berti Zequeira who make it their business to rescue the rejects.

Lionel Muller, senior vice president at Hipodromo Camarero, Puerto Rico's only racetrack, said owners generally have the horses killed only as a last resort when they cannot find a suitable second home.

"Most of the horse owners really love the horses. You don't want to get rid of a horse that way," he said.

With a stable of about 1,300 horses, the flower-trimmed track on the north coast holds races five days a week. Tourists and other fans cheer from open-air grandstands and a skybox restaurant. About $210 million a year is bet at the Hipodromo and at off-track betting booths.

The U.S. horse racing industry also struggles with unwanted thoroughbreds. AP's efforts to obtain figures were unsuccessful, but advocacy groups say sanctuaries created over the past two decades have dramatically cut the likelihood that a former racer will be executed.

"If you're a thoroughbred and you're not dangerous to humans, there's a home out there for you," said Gail Hirt, a Michigan-based board member of the Communication Alliance to Network Thoroughbred Ex-Racehorses.

Horses that don't win in Puerto Rico quickly become liabilities for their owners. It costs about $750 a month in food and stable fees to keep a thoroughbred at the track, and many owners would rather spend on horses that still have a chance of winning.

Farms and ranches that could take retired horses often prefer lower-maintenance breeds such as the Paso Finos, bred locally since Spanish colonial times and prized for their smooth gait.

That often leaves euthanasia as the cheapest option. The clinic charges owners only about $20 for the chemicals, Garcia said.

The sport attracts many small-time businessmen such as Maldonado, who devotes most of his time to running a booth at a flea market in nearby Rio Grande. Garcia said many take on more horses than they can afford in hopes of striking it rich.

"A lot of times people will have good luck with one horse, that horse will make them a lot of money, and they feel they can do that with every horse," he said. "What ends up happening is this renewable resource, which is the racehorse, ends up being treated like just another raw material. When it doesn't produce, you toss it away. And that's sad."

The thoroughbreds, mostly imported from the United States, often begin racing before their third birthday. After a brief career on the track, they can live to 30 or older.

But veterinarians say they would rather see unwanted horses destroyed humanely than given away or sold to somebody who cannot afford to feed and care for them.

Some horses wind up fending for themselves. Emaciated thoroughbreds, marked by tattoos from the track, have been found among the "chongos"_ stray, mixed-breed nags _ chewing grass by the roads, according to Amigos de los Animales, an animal sanctuary.

Zequeira has saved dozens of horses. He retrains them at a farm nestled against a mountain ridge in eastern Puerto Rico as sport jumpers for equestrian contests, then sells them or gives them away.

"What they do with horses, that's not human," he said.

The horses can take months _ even years _ to become docile. But trainers say even the hot-tempered thoroughbreds can adapt.

One gray gelding, Divo, whose racing career was cut short because he was too temperamental, is now gentle enough for 12-year-old Claudia Colon. The two have won blue ribbons at jumping contests. Still, Divo does retain some of his wild streak.

"He can be crazy," Claudia said, twirling a white lock of hair on his forehead. "He has his moments."

The vast majority of horses have no such luck.

"Unfortunately, the racehorse industry is dealing in an expendable commodity," said Keith Dane, director of equine protection for the Humane Society of the United States. He said his group would like more alternatives for the horses "rather than see them wasted in this way."