By BETH HARRIS
AP Racing Writer
LOUISVILLE, Ky. -- The dirt will be flying when 20 horses stampede around the first turn at the Kentucky Derby, and more than 150,000 fans will hear the thundering of hooves down the stretch to the finish line.
That sight and that sound would be gone if Churchill Downs went the way of other tracks in Kentucky, California and Illinois -- replacing dirt with a synthetic surface made of wax-coated sand, fibers and recycled rubber.
The synthetic surface mutes hoofbeats -- as classic a sound in horse racing as the bugler's "call to the post" -- and limits whatever stuff might fly in the faces of the trailing horses.
From horses to trainers to jockeys to bettors, the debate is vigorous on whether synthetic surfaces are the future of North American racing.
Southern California's three major tracks -- Santa Anita, Hollywood Park and Del Mar -- installed new surfaces under a state mandate. Arlington Park, outside Chicago and owned by Churchill Downs, did too, along with Kentucky's Keeneland and Turfway Park, and Fair Hill Training Center in Maryland.
This year's Breeders' Cup at Santa Anita will be the biggest racing event staged on a synthetic track.
But dirt still rules in Louisville, New York and Florida.
"It's probably premature to determine whether it's here to stay or not," trainer Todd Pletcher said. "We're all kind of learning as we go along, and what we're finding is that there's a lot that we don't know about it."
The new materials are designed to better protect animals and jockeys from catastrophic injuries, a necessity no one disputes. A new on-track injury reporting program seems to indicate the surface is having the desired effect.
Reports by veterinarians at 34 tracks across the country between June 2007 and early this year showed synthetic tracks averaged 1.47 fatalities per 1,000 starts, compared with 2.03 fatalities per 1,000 starts for horses that ran on dirt.
"I'm a big fan of synthetic tracks," said Eoin Harty, who trains Derby contender Colonel John. "The tracks in California were very unsafe for too long. The proof is in the pudding. The field sizes have swelled and the horses have stayed sounder longer."
Some of the 20 horses expected to run in Saturday's 134th Derby have never raced on dirt, notably Colonel John, or have switched between dirt and synthetics with varying results. Pyro, for example, has never run poorly on dirt, but finished 10th in his final Derby prep on Keeneland's synthetic surface.
"(Synthetic) to dirt, I've had some success," said Steve Asmussen, who trains Pyro. "Dirt to (synthetic), I haven't had any."
Like Pyro, all of the dirt graded-stakes winners in the Blue Grass faltered, while Pletcher's colt Monba maintained his form on synthetics and won.
But some handicappers and bettors complain the synthetics, which go by such brand names as Polytrack and Cushion Track, don't provide a true, uniform surface on which to judge a horse's past performances. Ticking off the betting public could prove disastrous in a sport hungry for fans outside the Triple Crown races.
"It certainly is a concern to me that the handle seems to reflect that the big bettors don't have confidence in the surface," Pletcher said. "Ultimately, we all know that that's what generates the purses and we need their confidence in the surface for it to be successful."
Trainers debate the consistency of synthetic surfaces, but they, along with track superintendents, like their ability to hold up under adverse conditions. Trainers don't worry whether rain will disrupt their horses' workouts on synthetic tracks, while dirt can turn into a dangerous quagmire.
However, Santa Anita in Arcadia, Calif., had such severe drainage issues with its new track after heavy winter rains that it was forced to reformulate the ingredients, leaving no one sure what to call the surface.
"We're trying to get some of those objective parameters as to what actually constitutes a synthetic track," said Rick Arthur, a veterinarian and adviser to the California Horse Racing Board. "Was Santa Anita's track in December and January a synthetic track? It had some odd material in it, but it certainly didn't seem to behave like other synthetic tracks."
Training horses on synthetic tracks can require different tactics than on dirt.
"You got to get your horse to relax and you can't ask them for so much speed (on synthetics)," Harty said. "You've got to save something for the latter stages of the race."
At Keeneland's spring meeting, Pletcher thought the synthetic surface was consistent for the first time since it was installed in 2006.
"It's becoming a little more of a fair track where you can let the horse run their own natural style," he said.
Rookie Derby trainer James Kasparoff will saddle Bob Black Jack, a veteran of California's synthetic tracks.
"You come off synthetics and your fitness level is very, very high," he said. "Synthetic tracks are a little different, horses use a different set of muscles. When Bob Black Jack gets on the dirt, there won't be any problem with it, he'll probably fly over that stuff."
Churchill Downs officials are carefully watching tracks that have switched surfaces, mindful of how such a change could affect the home of the nation's oldest continuous sporting event.
"We've never been against the synthetic surface -- we've got so much tradition with Churchill Downs," track superintendent Butch Lehr said.
Pletcher will try to snap an 0-for-19 Derby losing streak with Monba and Cowboy Cal, his 1-2 Blue Grass finishers on a synthetic surface.
"Probably the best horse is going to win, whether they prepare at Palm Meadows or Churchill or Keeneland or what-have-you," he said. "The most important thing is to show up with a healthy horse that's ready to run."
No matter what it runs on.
AP Sports Writer Will Graves contributed to this report.