From Blood Horse:

Barbara Borden, chief steward for the Kentucky Horse Racing Commission issued the following statement:

"The riders of the 18 and 20 horses in the Kentucky Derby lodged objections against the seven horse, the winner, alleging interference turning for home leaving the quarter pole. We had a lengthy review of the race, interviewed affected riders and determined that the seven horse drifted out and impacted the number 1, who in turn interfered with the 18 and 21. Those horses were all affected. Therefore we unanimously determined to disqualify number seven and place him behind 18. That is our typical procedure."