"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.''

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