In addition to surgeries, the cats are vaccinated against rabies, treated for fleas, ticks and worms, fitted with microchips, and given other medical care that advocates say will make them healthier, happier, and, in general, better neighbors.
"It's public health for kitties," said Denise Bash of the Warrington-based support agency Animal Lifeline, one of the agencies involved with the program. "We're trying to make this a safer place for everybody."
Bash and others taking part in the program hope to treat from 150 to 200 cats before the end of the week, said Sarah Eremus of the SPCA.
The Trap Neuter Release system is poised to become the leading method of animal control in the country, said Elizabeth Putsche, a staff attorney with the national organization Alley Cat Allies, which is based outside Washington.
When cats are removed from an area and euthanized, often some remain and continue breeding, she said. Even when all cats are cleared out, she said, inevitably more move in, and the problems begin anew.
Spaying and neutering the felines stabilizes the population, she said, and also lessens fights, spraying, and other behavior associated with non-neutered cats.
"It's great because it's humane, but it's also the most effective form of animal control that we have," Putsche said. "It breaks the cycle of unvaccinated, un-neutered cats."
Parx chief operating officer Joseph Wilson said the area had been home to cat colonies since before the racetrack was built, and that the casino had implemented a similar program several years ago.
"There's a need for them to be managed so there's not a bunch of sick cats running around," he said Wednesday, standing near 30 or more meowing cats that were in cages and plastic carriers near the stables. "And kittens."
In addition to passing disease to the horses, the cats could pose dangers to riders on the track. In April, a Philadelphia jury in a wrongful-death lawsuit found Parx liable for nearly $8 million for a 2010 accident in which a jockey was killed after a chicken ran onto the track and startled his racehorse. The jury found Parx negligent in failing to keep the track clear.
In addition to the feral cats, some socialized cats live in the stables and have forged relationships with Parx employees, Eremus said. This week, some of those workers have brought in their resident barn cats for treatment.
Analyte Peraza, 34, who works as a horse walker, dropped off a second cat Wednesday afternoon. She said the orange tabby appeared recently in the stable where she works, hungry for companionship. Soon, he became known as Buddy.
"He's so friendly. I think he's a house cat and somebody threw him away," she said. "We try to feed them every day, but we worry about their health."