Kentucky Derby winner California Chrome arrives Monday at the Pimlico Stakes Barn for Saturday's 139th running of the Preakness Stakes. (Doug Kapustin/For The Washington Post)

The filly who could have won the Preakness won’t be in Baltimore on Saturday.

Untapable captured the Kentucky Oaks in sensational fashion, a performance significantly faster than California Chrome’s Kentucky Derby victory the next day. But trainer Steve Asmussen and owner Ron Winchell decided almost immediately against challenging males in the Preakness. “It is not in her interests to run back in two weeks,” the trainer said.

Asmussen, who won the Preakness with Rachel Alexandra under similar circumstance in 2009, presumably knows what’s best for his filly. But his reluctance to run a top horse in the Preakness after a two-week rest is part of a trend in the sport. Only three of the Derby’s 19 starters will be in the field. The colts who finished 2-3-4-5-6 will not challenge California Chrome.

Asmussen’s decision is as disappointing as the one made last year by Chad Brown, trainer of Normandy Invasion, who was almost every wise-guy handicapper’s pick to win the Preakness. The colt had made a bold premature move into the teeth of a fast pace before weakening to finish fourth in the Derby. Brown and owner Rick Porter hemmed and hawed about the Preakness before deciding not to run. “Coming back in two weeks would be a mistake long-term,” Porter said. The decision was subject to even more second-guessing when Oxbow , who had finished six lengths behind Normandy Invasion in the Derby, won at Pimlico.

The belief that horses need lengthy rest between races has become part of the orthodoxy of the sport. It’s a radical change from the past. In the 1950s and ’60s, good horses often raced with a week’s rest (or less). Now 3-year-olds get their final prep race three, four or five weeks before the Derby, and so the 14-day layoff before the Preakness looks like a daunting challenge.

Why do modern-day thoroughbreds need such gentle handling? The change in training philosophy may have occurred because horses are less robust than their forebears. It may have to do with the almost-universal use of Lasix; the diuretic causes horses to lose significant weight, and they need time to recover from a race. Many leading trainers are believers in the Ragozin Sheets and the Thoro-graph speed figures, both of which espouse the philosophy that horses will “bounce” — i.e., run an inferior race — if they run back too quickly from a peak effort. Five-time Preakness-winning trainer Bob Baffert believes that the Derby’s now-common fields of 20 horses puts so much stress on runners that they need more time to recover than the Preakness allows.

Art Sherman, the 77-year-old trainer of California Chrome, remembers how the game used to be played. As a youngster, he was the exercise rider for the great racehorse Swaps, who in 1956 set a world record for 11 / 16 miles, then made three more starts in the next month, winning them all and setting another world record. Swaps didn’t need much rest between races and he never bounced. Yet Sherman, too, has embraced the modern thinking. He now says, “I never run a horse back in two weeks even when I’m running cheap claimers . . . I’m a guy who likes to go seven to eight weeks between races.”

Because the trainer of a Derby winner will almost always take a shot at the Triple Crown, the Preakness is one of the few races in which top horses will run with two weeks’ rest. The results at Pimlico contradict the belief that this short layoff is too difficult for the horses.

Kentucky Derby winners regularly come back to deliver smashing performances in Baltimore: Funny Cide (2003) won by nearly 10 lengths, Smarty Jones (2004) won by 111 / 2 Big Brown (2008) by 51 / 2. In 2012 I’ll Have Another and Bodemeister finished 1-2 in the Derby, then ran much faster in the Preakness and finished 1-2 again. None of them bounced. When Derby winners have flopped in Baltimore — such as Orb in 2013■ and Super Saver in 2010 — the explanation may be that they benefited from perfect trips at Churchill and didn’t get such an easy setup at Pimlico.

Despite such evidence, trainers remain fearful of the 14-day layoff, and the Preakness has suffered as a result. Some of the greatest races of all time have been rematches between the 1-2 finishers in the Derby: Affirmed vs. Alydar (1978), Alysheba vs. Bet Twice (1987), Sunday Silence vs. Easy Goer (1989). But now, more often than not, well-regarded losers don’t come back for a rematch. “The last two years have very definitely been a struggle for us,” said Tom Chuckas, president of the Maryland Jockey Club.

The conservative management of top horses not only hurts a sport that needs its stars to race against each other; it can hurt the trainers and owners who think they’re being prudent by not competing.

When he opted to skip the Preakness last year with Normandy Invasion, Porter said, “Our goal is to have a fresh horse” for races at Saratoga in August. But after passing up a golden chance to win a Triple Crown race, Normandy Invasion developed a foot abscess that prevented him from running at Saratoga; he was out of action for the remainder of his 3-year-old season.

Perhaps skipping the Preakness will work to the long-term advantage of Untapable and the Derby runners who are absent from Baltimore. But patience and prudence are not necessarily rewarded in racing, as the example of Normandy Invasion demonstrated. Sometimes the wisest strategy is to strike while the iron is hot.

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