RUIDOSO, N.M. — At 2:11 p.m., as two ambulances waited with motors running, 10 horses burst from the starting gate at Ruidoso Downs Race Track 6,900 feet up in New Mexico’s Sacramento Mountains.

Nineteen seconds later, under a brilliant blue sky, a national champion jockey named Jacky Martin lay sprawled in the furrowed dirt just past the finish line, paralyzed, his neck broken in three places. On the ground next to him, his frightened horse, leg broken and chest heaving, was minutes away from being euthanized on the track.

For finishing fourth on this early September day last year, Jacky Martin got about $60 and possibly a lifetime tethered to a respirator.

The next day, it nearly happened again. At virtually the same spot, another horse broke a front leg, pitching his rider headfirst into the ground. The jockey escaped serious injury, but not the 2-year-old horse, Teller All Gone. He was euthanized, and then dumped near an old toilet in a junkyard a short walk from where he had been sold at auction the previous year.

In the next 24 hours, two fearful jockeys refused their assigned mounts. The track honored two other riders who had died racing. As doctors fought to save Mr. Martin’s life, a sign went up next to the track tote board: “Hang in there, Jacky. We love you.”

On average, 24 horses die each week at racetracks across America. Many are inexpensive horses racing with little regulatory protection in pursuit of bigger and bigger prizes. These deaths often go unexamined, the bodies shipped to rendering plants and landfills rather than to pathologists who might have discovered why the horses broke down.

In 2008, after a Kentucky Derby horse, Eight Belles, broke two ankles on national television and was euthanized, Congress extracted promises from the racing industry to make its sport safer. While safety measures like bans on anabolic steroids have been enacted, assessing their impact has been difficult because many tracks do not keep accurate accident figures or will not release them.

But an investigation by The New York Times has found that industry practices continue to put animal and rider at risk. A computer analysis of data from more than 150,000 races, along with injury reports, drug test results and interviews, shows an industry still mired in a culture of drugs and lax regulation and a fatal breakdown rate that remains far worse than in most of the world.

If anything, the new economics of racing are making an always-dangerous game even more so. Faced with a steep loss of customers, racetracks have increasingly added casino gambling to their operations, resulting in higher purses but also providing an incentive for trainers to race unfit horses. At Aqueduct Racetrack in Queens, the number of dead and injured horses has risen sharply since a casino opened there late last year.

Mr. Martin’s injury occurred in a state with the worst safety record for racetracks, a place where most trainers who illegally pump sore horses full of painkillers to mask injury — and then race them — are neither fined nor suspended and owners of those drugged horses usually keep their winnings.

The failure of regulators to stop that cheating is reflected in the numbers. Since 2009, records show, trainers at United States tracks have been caught illegally drugging horses 3,800 times, a figure that vastly understates the problem because only a small percentage of horses are actually tested.

In the same period, according to the Times analysis, 6,600 horses broke down or showed signs of injury. Since 2009, the incident rate has not only failed to go down, it has risen slightly.

The greatest number of incidents on a single day — 23 — occurred last year on the most celebrated day of racing in America, the running of the Kentucky Derby. One Derby horse fractured a leg, as did a horse in the previous race at Churchill Downs. All told, seven jockeys at other tracks were thrown to the ground after their horses broke down.

A state-by-state survey by The Times shows that about 3,600 horses died racing or training at state-regulated tracks over the last three years.

In one 13-day stretch of racing in 2010 at Sunland Park Racetrack and Casino in New Mexico, nine horses died racing, five were hauled away in ambulances and two jockeys were hospitalized, one in critical condition.

“It’s hard to justify how many horses we go through,” said Dr. Rick Arthur, the equine medical director for the California Racing Board. “In humans you never see someone snap their leg off running in the Olympics. But you see it in horse racing.”

Even some of America’s most prestigious tracks, including Belmont Park, Santa Anita Park and Saratoga Race Course, had incident rates higher than the national average last year, records show.

Why racehorses break down at such a high rate has been debated for years, but the discussion inevitably comes back to drugs.

Laboratories cannot yet detect the newest performance-enhancing drugs, while trainers experiment with anything that might give them an edge, including chemicals that bulk up pigs and cattle before slaughter, cobra venom, Viagra, blood doping agents, stimulants and cancer drugs.

Illegal doping, racing officials say, often occurs on private farms before horses are shipped to the track. Few states can legally test horses there.

“They are pharmacist shops,” said Dr. George Maylin, the longtime head of New York State’s testing laboratory. “Nobody has any control over what they are doing.”

Even so, legal therapeutic drugs — pain medicine in particular — pose the greatest risk to horse and rider. In England, where breakdown rates are half of what they are in the United States, horses may not race on any drugs.

At higher levels, pain medicine can mask injury, rendering prerace examinations less effective. If a horse cannot feel an existing injury, it may run harder than it otherwise would, putting extra stress on the injury. As many as 90 percent of horses that break down had pre-existing injuries, California researchers have found.

“This is just a recipe for disaster,” said Dr. Tom David, who until this year was chief veterinarian for the Louisiana Racing Commission. “Inflamed joints, muscles and mild lameness are masked by medication and therefore undetectable to the examining veterinarian.”

While high-profile Triple Crown races get the most attention, the mainstay of racing in America is the lower tier, so-called claiming races. Horses in these races are most vulnerable, in part because regulators often give them less protection from potentially dangerous drugs.

The Times analysis found that horses in claiming races have a 22 percent greater chance of breaking down or showing signs of injury than horses in higher grade races. That lower level of race has been particularly affected by the arrival of casinos.

At Aqueduct, most of the 16 horses that have died so far this year were in the lower ranks, where purses have increased the fastest because of new casino money.

“It’s hard to watch these poor animals running for their lives for people who could really care less if they live,” said Dr. Margaret Ohlinger, a track veterinarian at Finger Lakes Casino and Racetrack in upstate New York. She performs pre-race inspections and treats horses injured in races but is not responsible for their overall care.

Last year at the track, Dr. Ohlinger counted 63 dead horses. That, she said, is more than double the fatalities of five years earlier.

Oversight Undermined

Race officials have always done their best to hide fatal breakdowns, erecting screens around fallen horses and then refusing to disclose the tracks’ accident rates.

But amid criticism that individual state racing commissions lacked the will to make the sport safer, and the threat of federal oversight, the industry promised changes, including new restrictions on the use of drugs, a program to accredit racetracks and drug-testing laboratories and uniform rules for punishing drug violators.