In the paddock, 10 horses circle, models strutting on a runway, on display one last time for the gamblers to ogle before they place their bets. Shiny and sculpted, the Thoroughbreds revel in the attention, their magnificent beauty making the humans around them seem small. They are born to compete, and they show it in how they flatten their ears when behind by a length or bite a challenger who gets too close or stretch their necks to win by a nose and then pose for the cameras afterward. At the moment, Canady is judging them for the final time too, searching for a limp or bob or any sign of injury. This is her second inspection of the day, the hands-off kind. Hours earlier, she administered a more rigorous exam, feeling legs and joints for signs of injury. Now she must catch anything she might have missed. She watches the animals closely as they're led out to the track, then climbs into her truck, giving each a final look as the grooms cram them, one by one, into the green starting gates ...

And they're off.

So is Canady, crouched in the driver's seat, hands at 10 and 2, seat belt undone, the Tundra trailing the horses from the dirt as they run on the turf. Her blue eyes flip between the stampede and the road, the truck fishtailing as it accelerates. Next to her in the front seat is Waverly Parsons, the track chaplain, who, minutes earlier, administered a prayer for the owners, trainers, jockeys, grooms and horses. On the floor behind them is a black metal equine leg splint, big as a ski boot. On the backseat, the black medical bag.

Rounding the first corner, Canady is silent and tense, as she is during every one of the 10 races she works each day. She can't usually drive faster than 30 mph without tearing up the road, so most of the horses have far outpaced her. A quarter mile ahead, jockey Francisco Torres is saddled on Heelbolt, winner of his previous three races.

Suddenly, Torres feels a jolt and hears a pop, like a bat hitting a softball. He will later say Heelbolt "took a bad step" -- jockeys always say the horse took a bad step. Heelbolt pulls up, hobbling as he slows from 40 mph to a stop. A scared Torres leaps off, landing several yards away.

As Canady rounds the second corner in her truck, the radio attached to her belt, labeled Vet 1, screams, "A horse is down! A rider is down!" She hits the gas.

Every eye is on her.

THEY DON'T shoot horses anymore. They used to, back when horse racing mattered, back when it grabbed America like football does now, when a day at the track meant dressing for church, with men in suits and women in hats, back when it was more about horses and less about money -- less about us. In 1973, when Secretariat won the Triple Crown, about $4.5 billion was wagered annually on horse racing. That number has since grown to nearly $14 billion. And yet the sport flashes on and off our radar now, briefly catching our attention when a Funny Cide or Smarty Jones threatens to make history, or, more tragically, when death comes to the track -- as it did for Eight Belles at last year's Kentucky Derby -- and we're reminded that one of our country's oldest sports is one in which the athletes sometimes die during competition.

Left to do the killing are the track vets, the people who pride themselves on being the strongest advocates for the horses, the people who don't give a damn about the money. "We police the sport," Canady says. It's often a thankless job. The starting salary for a regulatory vet is about $55,000, with 10-hour days the norm. There is constant, unspoken pressure not to scratch horses from competition; some owners yell at trainers who ask vets to look for injuries. While Canady is warm to most owners, she is pals with few. "You have to be friendly," she says, "but not friends."

Euthanizing horses is a small part of the job -- nationally, 1.5 out of every 1,000 must be put down because of injuries sustained on the track, according to the Association of Racing Commissioners International -- but it's the worst part. Dean Richardson "cried for days" after euthanizing his most famous patient, Barbaro. David Fitzpatrick, chief vet for the Illinois Racing Board, tears up as he talks about horses he's put down. Celeste Kunz, the emergency vet at the Meadlowlands in New Jersey, cried when Eight Belles suffered that fatal injury -- and she was watching the Derby from home. "It felt like every horse I've ever lost died that day," Kunz says. After Canady put down a foal with terminal birth defects, she "didn't talk to anyone for days."

Death can be spooky. In 1993, Kunz was working at Jersey's Monmouth Park, where mist and fog blow off the Atlantic Ocean onto the beachside track. Visibility was awful, but competition rarely stopped. After one race, Kunz counted nine horses at the finish; 10 had started. She took off on foot, walking the track with her medical tool kit, squinting through the mist until she saw a shadowy figure, already a ghost: It was a gray and white horse with a fractured ankle, waiting for someone to end his misery.

Death can be mystifying. In 2004, when Canady was working at Finger Lakes Race Track in upstate New York, she got word that a horse had been injured on a hot walker, a carousel that slowly leads the animals in circles to cool them down. When she arrived, the vet saw one of the horse's hind legs had snapped in half, but she couldn't figure out how. There were no other horses nearby, no holes in the ground, no rails that might have been kicked. "The leg just broke," Canady says with a sad shrug.

Death can be contagious. Earlier this year, seven horses had to be euthanized in two weeks at Santa Anita. Critics blamed the synthetic surface, which the California Horse Racing Board had mandated for all major tracks to improve safety. By and large, the new surface had worked, reducing deaths from catastrophic injuries statewide from 3.01 per 1,000 in 2007 to 2.29 last year. But all of a sudden horses were dropping at an alarming rate, the public was wondering why, and Santa Anita officials didn't have an answer. Then, as inexplicably as the breakdowns started, they stopped. Only two horses in the next 68 days were euthanized.

More than anything, death can be hard to shake. Most veterinary schools don't teach students how to cope with it. The American Association of Equine Practitioners doesn't have a support line to call. Vets just suck it up and go, using medical necessity as a shield. Kunz has learned to hide her feelings in those hectic moments. Still, a "nervous, energetic fear" courses through her body as she injects a horse with that toxic solution. "The decision to euthanize is scary," she says. "You're really isolated on the track. There are no other vets with you. But you can't go to pieces because you have to be there for the horse."

That's why these vets picked this career -- because they love horses enough to suffer for them, because they understand that death is sometimes better than life. They know that a broken bone is often a death sentence for an animal whose internal organs, including digestive and circulatory systems, are dependent on continued mobility. Casts and slings restrict movement and prevent those organs from functioning properly, leading to life-threatening diseases. As a result, Kunz says, "the cases where we euthanize a horse are black and white."

Death by lethal injection comes in about a minute, which seems very peaceful, very quick. So it's stunning to hear many vets say that this method isn't in the best interests of the horse. They would rather ditch the pink and do the killing in the way they deem most humane.

With a gun.

Derby winner Barbaro shattered a hind leg at the Preakness and would later be put down by lethal injection. Matthew Stockman/Getty Images

THE TRUCK slides to a stop. Canady sees Heelbolt, standing 15 yards away. He's a gorgeous horse: glistening brown coat that darkens into black legs, speckles of white surrounding his eyes, a cowlick topping the crest of his head. He's exactly four months shy of his fifth birthday, April 1. He loves apples and carrots. He's so gentle, owner Ray Guarisco and trainer Sturges Ducoing can't recall his ever kicking anyone. But Heelbolt is competitive. He's done well over the past few months, prompting Guarisco, an equipment contractor in nearby Morgan City, to visit the track today. It's the first time the owner has seen his prize horse run in person.

Canady grabs the splint and the black bag, ducks under the railing and runs up the five-foot hill to the track. Two ambulances, one for the rider, one for the horse, are en route. Chaplain Parsons runs toward Torres, who is crumpled on the ground.

"Are you okay?" Parsons asks.

"I'm fine," Torres says. "Check on the horse."

Canady is almost there. This is the job she was born to do. She loved horse racing as a kid in New Castle, Pa. Although her parents insisted her middle name, Kelso, was shared coincidentally with the Hall of Fame Thoroughbred, she prefers to think it was fate. She graduated from Cornell vet school in 1997 and worked at tracks in the Northeast before moving to New Orleans. "All my life I've wanted to be around horse racing," says Canady, a single mom with a 7-year-old daughter. "You have to be a dreamer to work at a track. This is a dream for me."

As she nears Heelbolt, he is facing away from her. He's calm, but she can see he's standing on only three legs. His left front ankle is dangling and shattered, attached only by skin. Two arteries are split. Blood is everywhere -- on his leg, his hoof, the grass. Wow, this is a bad one. Canady has seen this type of injury before, and she's seen how horses react to it. Some grunt and snort and thrash. Others, seemingly unbothered, try to run. But in her 12 years as a vet, she has never seen a critically injured horse do what Heelbolt is doing now. Eating grass.

FOR HUNDREDS of years, there was no argument about the best way to kill a horse. Those injured in the chariot races of ancient Greece and Rome were presumably stabbed. With the introduction of the musket around the 15th century, and with European armies spreading firearms and horses all over the world, killing an injured horse with a gun became accepted practice. It was quick, cheap and easy -- never mind that bullets often ricocheted out of the horse's head or that men might make the mistake of shooting the animal between the eyes. (A horse's brain is located toward the back of the head. To find it, draw a line from the outside of one eye to the opposite ear, then do the same from the other eye; where the lines intersect is the brain.)

In 1930, vets started using the Bell Gun, one of the first tools designed to kill livestock in a clean, safe, precise way. It weighed five pounds, spit .32-caliber bullets and had a bell-shape protective cover over its muzzle. To use it, vets simply fit it onto a horse's forehead, unscrewed a slot, inserted a bullet and tapped a lever. No kickback and no mess, only a sharp pop from point-blank range.