Todd Pletcher has nominated 42 three-year-olds for the Kentucky Derby which has received 413 entries, the highest for five years.
Prominent among the Pletcher nominees is Coolmore's Havana with the organisation's Irish trainer Aidan O'Brien entering four for the team.
They are Breeders' Cup Juvenile Turf runner-up Giovanni Boldini, Michaelmas, Sir John Hawkins and Oklahoma City.
Fellow Irishman Dermot Weld has nominated Free Eagle, who is third favourite for the Epsom Derby, Fascinating Rock, Gambrinus and Good Tradition in the three triple crown races comprising the Derby, the Preakness and the Belmont Stakes.
European bookmakers have the Jerry Hollendorfer-trained Shared Belief, last season's champion two-year-old, as the 12-1 favourite.
Pletcher won the 2010 Kentucky Derby with Super Saver. His other triple crown winners are Rags To Riches in the 2007 Preakness and Palice Malice in last year's Belmont.