No major Triple Crown preps were run last week — the Sham was postponed when Santa Anita cancelled Saturday’s card because of heavy rain — so now’s a good time to look back at a system for handicapping the Kentucky Derby that was very popular in its day; but which, like all systems, seems to have outlived its usefulness.

Twenty-five years ago, Spend a Buck blitzed the Derby gate to wire, winning by 5 1/4 lengths over a field that included 2-year-old champ Chief’s Crown, who would go on to win the Travers and Marlboro Cup; Preakness winner Tank’s Prospect; and two future Breeders’ Cup Classic winners, Proud Truth and Skywalker.

Some say the race might have been different if Eternal Prince, the other speed horse in the race, didn’t miss the break. But Spend a Buck’s fractional times were among the fastest in Derby history: a half-mile in :45 4/5, six furlongs in 1:09 3/5, a mile in 1:34 4/5.

As the second choice behind 6-5 favorite Chief’s Crown, Spend a Buck paid $10.20. Finishing second, a half-length in front of Chief’s Crown to complete a $118.20 exacta, was Stephan’s Odyssey. It was an easy game back then. Spend a Buck and Stephan’s Odyssey were the only two contenders in the field that year, according to a controversial system championed by Daily Racing Form’s “Bloodlines” columnist, Leon Rasmussen, called the “Dosage Dual Qualifiers.”

To be a dual-qualifier, a horse must 1) be the highweight, or ranked within 10 pounds of the highweight, on the Experimental Free Handicap that lists the previous season’s top 2-year-olds; and 2) have a Dosage Index of 4.00 or lower.

The Dosage Index, invented by Dr. Steve Roman, is figured using a formula based on the chefs-de-race (influential sires) in a horse’s four-generation pedigree. Chefs-de-race are classified into five categories ranging from speed to stamina. The lower the DI, theoretically, the more stamina the horse should have.

From the mid-1980s through the late 1990s, the Dosage System did very well predicting Derby winners, including longshots Ferdinand, Alysheba, Unbridled, Sea Hero, Go for Gin and Thunder Gulch, while eliminating heavy favorites like Snow Chief and Holy Bull.

Since Silver Charm in 1997, however, the only dual qualifier to win the Derby was Street Sense. The “non-qualifying” winners either did not accomplish enough as 2-year-olds to rank near the top of the Experimental, or had a Dosage Index over 4.00. (The chef-de-race list is no longer updated as it was before Rasmussen died.)

As for this year’s Run for the Roses on May 1, those who still follow the Dosage System have plenty to choose from. Here are the 2010 dual qualifiers, according to Dr. Roman’s website, chef-de-race.com, that are possible Derby starters: Lookin at Lucky, Vale of York, Noble’s Promise, Buddy’s Saint, Super Saver, Aikenite, D’Funnybone, Dublin, Interactif, Homeboykris and Discreetly Mine.