A dramatic sub-plot has developed around which horses will actually get to run in the Derby. Traditionally, for business, social, and sporting reasons, an owner did not enter a horse in the Derby unless he or she thought that it had a reasonable chance to win. It costs money to enter, and it doesn't make economic sense to use one of a valuable horse's limited number of career starts in a futile effort in an especially exacting race. Moreover, it was considered both a disgrace to have your horse exposed as outclassed and a disservice to the horse to ask it to make an all-out effort in a demanding race against superior competition. Few owners wanted to look like fools or as if they were putting their own desire to be part of a Derby ahead of their horses' welfare.
Gradually, owners have come into the sport/business of racing for whom the glamor and excitement of running a horse in the Derby supersedes all other considerations. Some owners now regard owning a horse that ran in the Derby as an achievement in itself. As a result, Churchill Downs has had to limit the number of starters in the race to 20, as determined by earnings in graded stakes races, the highest quality races. Naturally, now that there is a competitive basis for qualifying to run, any remaining stigma attached to running a long shot in the Derby has faded, and most owners who have sound three-year-olds with top-twenty graded stakes earnings feel that their horses have earned the right to run. Thus, the twenty-horse ceiling has also become a twenty-horse floor. Each year, it seems that at least one talented, but late-developing, horse that would be one of the favorites to win the Derby is in danger of being excluded on the basis of qualified earnings. This year, that horse is Dunkirk, which has only made three career starts, but will be one of the betting favorites in the Derby-- if he gets to run.
An irony of this twenty-horse syndrome is that it enhances the chances of a long shot winning the Derby. With that many horses jostling for position to save ground on the turns, racing luck tends to play more of a role in Derbys than in most races. There has always been a lot of uncertainty in picking a Derby winner anyway, partly because the race is over a distance-- a mile and a quarter-- that, in most years, none of the horses have ever run in their young lives. I haven't checked lately, but at one time it was true that if someone had bet the same amount on every starter in every Kentucky Derby, he or she would be showing a profit.
