For the third time in seven years, the Kentucky Derby winner will not run in Preakness Stakes, bringing up the question of whether the races should be spread out.

Thirteen horses have won the Triple Crown in American Thoroughbred racing history. Here's a look at the winners and the history of the Triple Crown:

Aidan Butler went to battle, fighting to rework the Triple Crown’s coordinated calendar. The president of 1/ST racing, which owns and operates Pimlico Race Course, wanted to give Kentucky Derby participants ample time to recover rather than forgo the Preakness for the Belmont Stakes.