This is the story of two horsemen.

Scratch that. It’s the story of two trainers. Only one is a horseman.

Both trainers had cause to celebrate last weekend. John Shirreffs brought undefeated Zenyatta to Del Mar for the Grade I Clement Hirsch Stakes on Aug. 7. He did so despite his strong reservations about the problematic Polytrack surface, which, when scooped by the handful, looks like the contents of a vacuum cleaner bag.

An hour before the race, Shirreffs was still fretting about the track surface and debating whether or not to run the 6-year-old mare, even though a late scratch would have prompted an unprecedented revolt from the 32,000-plus in attendance (and possibly great bodily injury to Shirreffs in the form of thrown Manolo Blahniks).

In the end, Zenyatta made a show of it, winning her third straight Clement Hirsch in typical, heart-stopping fashion and running her record to 18-0 before heading to the barn for her favorite post-victory treat — a pint of Guinness Extra Stout poured into a Tupperware bowl and held patiently by Shirreffs.

Doug O’Neill, meanwhile, won the Grade III Sorrento Stakes the day before with Wickedly Perfect, a filly owned in part by STD Racing Stables, also the majority owners of O’Neill’s recently-retired superstar Lava Man.

O’Neill, 42, who has won 23 training titles at the California tracks since 2002, seems on his way to adding another. Through Aug. 12, he was leading the Del Mar trainer’s standings with 16 wins from 58 runners (28 percent winners) and proving to be the horseplayer’s best friend with 62 percent of his horses finishing in the money.

One horse that failed to finish in the money for O’Neill at Del Mar was the 5-year-old mare Burna Dette. A daughter of the leading California stallion, Unusual Heat, Burna Dette was clearly a horse on the decline. After showing promise on the grass early in her career, Burna Dette, who had won two races from 20 starts and $136,900, had already plummeted to the $25,000 claiming level when O’Neill claimed her at Hollywood Park on June 24 for owner Gregg Guiol. He ran her back in a $16,000 claimer at Del Mar on July 21 — opening day — where she finished next to last.

The night of Wickedly Perfect’s Sorrento win, Burna Dette was in the paddock at Los Alamitos Racecourse in Cypress, some 80 miles north, where she was scheduled to run in a $2,000 claiming race. The contrast between Del Mar, the seaside racing mecca and beautiful people magnet, and Los Alamitos, where the richest thoroughbred race is a $5,000 claimer, is stark even without considering the fate of the horses.

Whether or not O’Neill was considering Burna Dette’s fate that night is anyone’s guess. The B-52s were playing in the Del Mar infield, and O’Neill was observed bustin’ a move to the strains of “Love Shack.”

Bet down as the 4-5 favorite in the four-and-a-half furlong race, Burna Dette labored to keep up with the field. Rounding the turn, she broke down and fell, throwing jockey Cesar DeAlba to the track. DeAlba was not injured; Burna Dette was euthanized. She was also claimed out of the race by trainer Vod Farris.

Catastrophes like this often result in temporary outrage that is mostly restricted to Internet racing forums. The California Horse Racing Board is said to be reviewing the circumstances surrounding Burna Dette’s breakdown — reportedly, radiographs and scans taken while the mare was under O’Neill’s care have already been subpoenaed — but will be hard-pressed to prove culpability unless it can establish O’Neill knew Burna Dette was not fit for racing.

In the case of Burna Dette, it would appear, O’Neill was simply playing by the unspoken rules of the claiming game — unloading a deteriorating horse before she became completely valueless — and he wasn’t even playing very shrewdly. Most trainers are familiar with suspicious class drops, especially when executed by trainers known to play Russian Roulette with their horses.

O’Neill himself seemed to acknowledge as much last year when he was readying Lava Man for a comeback attempt after a year and a half in retirement.

“My owners treat this as a business,” said O’Neill, who claimed Lava Man for $50,000 in 2004 and wound up winning more than $5 million with him. “I love my horses, but they’re not pets. We don’t have the luxury of turning them out for a year. It’s better to just run them where we think they belong.”

O’Neill, who recently began sporting a fedora and white sport coat in an apparent attempt to channel Del Mar founder Bing Crosby, is something of an enigma. Relentlessly cheerful and unfailingly polite, O’Neill is often accompanied by his older brother and bloodstock advisor, Dennis (think “The Brothers McMullen” meets “Guys and Dolls”), at the races. A self-proclaimed family man, O’Neill’s outward persona seems to be at odds with the facts as they pertain to his career.

O’Neill was recently suspended 15 days after his horse Stephen’s Got Hope tested positive for an excess level of total carbon dioxide (TC02) following a seventh-place finish in the Illinois Derby. The elevated TC02 levels were the result of bicarbonate loading, or “milkshaking,” before the race. The process, which is prohibited in all racing jurisdictions, reduces lactic acid buildup and prevents fatigue. O’Neill has twice been suspended for milkshaking, in 2006 (when his horses earned $11,247,756, his most lucrative year to date) and 2008.

The California Horse Racing Board chose to honor Illinois’ ruling, and O’Neill was suspended from June 30 to July 15. This time, O’Neill chose not to allow his horses to run under assistant trainer Leandro Mora’s name — something he has done during previous suspensions. Was O’Neill sending a tacit message to the racing board that his absence would be felt at the entry box, where he averaged four to seven starters per day? Indeed, Hollywood Park was forced to cancel racing three times during the spring/summer meet because of insufficient entries. One of those cancelled cards fell during O’Neill’s suspension, on July 5. He still won the training title.

But it was O’Neill’s management of Lava Man, a fan favorite who had been retired in the summer of 2008 and then returned to racing in late 2009, that provoked the most ire. During his “retirement,” Lava Man underwent surgery to remove chips from his chronically sore ankles and then began receiving experimental stem-cell treatments.

He returned to the races in December, and failed to beat a horse in the San Gabriel Handicap. When he pulled up, the gelding’s hind legs were crimson; he was discovered to have “run down” on his heels. Lava Man was retired again but remained with O’Neill as a stable pony.

The Burna Dette tragedy highlights the need to change the current claiming rule, where ownership transfers once the gates open. Originally set up to allow trainers to run their horses at the appropriate level, claiming races are instead being used as a dumping ground for crippled horses. Track veterinarians are assigned to perform cursory examinations of all horses entered to race. Without access to the horse’s full medical history, this process is nothing more than a formality.

Last year, the California Horse Racing Board was considering adoption of a rule that would void claims of horses that could not return under their own power to be unsaddled after a race. That rule was eventually tabled. CHRB commissioner Bo Derek — yes, THAT Bo Derek — has called for a directive requiring that all medical records be turned over to the racing board when a horse dies at a California track.

Such rulings might have saved Burna Dette. Or the gelding Mi Rey, a classy old war horse who broke down badly in a $10,000 claimer on opening day at Del Mar last year, sending leading rider Rafael Bejarano to the hospital with a broken jaw and cheekbone. Mi Rey’s trainer? Doug O’Neill, for owners Gregg Guiol and Dennis O’Neill.

It’s too late for Burna Dette and Mi Rey. And it’s too late for a young jockey named J.C. Gonzalez, who died on the track at Fairplex Park on Sept. 9, 1999, after falling from a horse that should never have been allowed to race.

Gonzalez, 23, was riding the 4-year-old gelding Wolfhunt in a $5,000 claiming race at the Pomona bullring. Wolfhunt was dropping down from a $10,000 claimer. His trainer, Sandy Shulman, was notorious for unloading sore horses in cheap claiming races. The leading rider at the 1998 Fairplex meet, Gonzalez also had a reputation for riding horses others would not — accidents waiting to happen.

It happened, at 2:31 p.m.

Gonzalez and Wolfhunt were on the lead as they rounded the final turn of the 1 1/16-mile race. Suddenly, Wolfhunt went down, throwing Gonzalez to the track. As Gonzalez lay motionless in the dirt, Wolfhunt hobbled in aimless circles, his two ­broken front legs unable to support him. Gonzalez ­suffered massive head injuries when he was struck by passing hooves and was pronounced dead minutes later. Wolfhunt was euthanized on the racetrack.

Gonzalez’s parents sued Shulman, his vet and the track veterinarian, among others, alleging Wolfhunt’s known unsoundness before the race. Before all the facts could become public — the necropsy report showing Wolfhunt’s preexisting leg fractures, previous trainer Doug Peterson’s testimony that the gelding had serious knee problems months before his final race — the Gonzalez survivors settled out of court.

Whatever Faustian bargain O’Neill has struck, the fact is that he serves an important function in horse racing. He sends out horses. Lots of them. Through Aug. 12, O’Neill had saddled 614 starters nationally.

O’Neill stables 60 horses in Southern California. He recently sent 20 of his ­cheaper runners to Philadelphia Park, where they can ship in and race at smaller tracks. And with available horse inventory in Southern California down more than 25 percent (to 2,800 from 3,800 a year ago), it’s easy to see why O’Neill has been allowed to play fast and loose with the rules.

On Thursday, his work was again on display in the form of the 5-year-old gelding Big Wig, claimed by O’Neill on Aug. 4 for a partnership that included Dennis. O’Neill ran the horse back for $40,000 only eight days after the claim. He finished last and pulled up limping.

John Shirreffs, on the other hand, has sent out 62 starters this year. He has approximately 40 horses stabled at Hollywood Park and prefers to train over that surface rather than Del Mar’s, which has caused problems for some horses. Bob Baffert was forced to stop on nine of his 2-year-olds this year because of injuries suffered while training at Del Mar. Conato, trained by Jeff Bonde, had to be euthanized after suffering a spiral fracture of a hind leg in a July 28 allowance race.

“The horse was 100 percent sound before that race,” a crestfallen Bonde said. “On this track, if their foot plants, it doesn’t slide. It twists.”

For her next stop on the “Rachel Who?” tour, Zenyatta will likely run in … the Zenyatta Stakes (formerly the Lady’s Secret) at Santa Anita on Oct. 2. From there, she’ll go to Churchill Downs to defend her title in the $5 million Breeders’ Cup Classic before retiring to become a broodmare.

If a CHRB investigation finds that O’Neill knowingly ran an injured horse, the repercussions are likely to be felt nationwide. One person who would like to know just what O’Neill knew — and when he knew it — is the mare’s first trainer, Peter Eurton.

“She had a few issues behind, but we just turned her out,” said Eurton, who lost Burna Dette for $50,000 at Del Mar last year. “Nothing at all going on in front. She was really, really clean.”

Eurton said Burna Dette’s breeder, Jeff Stiefel, tried to buy the mare privately.

“He owns her whole ­family,” Eurton said. “He wanted to add her to the broodmare band. She was more valuable to us than them.”

On Aug. 8, two days after Burna Dette’s breakdown, Stiefel and his family were in the winner’s circle with Valley Cat, a gelding whose mother, Jane Blossom, is a full sister to Burna Dette.

“There were a lot of tears in that winner’s circle,” Eurton said.

O’Neill has been described as the kind of guy you’d want to have a beer with. Unless you're Zenyatta, and you already have the perfect drinking buddy.

The horseman.