Millionaire Sir Shackleton, who came within two lengths of Saint Liam in last year's Woodward Stakes (gr. I), will enter stud at Dr. Tony Ryan's Castleton Lyons near Lexington. The 5-year-old son of Miswaki won three graded stakes and placed in a three grade I events.Bred and raced by Tracy Farmer, and named for Antarctic explorer Sir Ernest Shackleton, Sir Shackleton won the Richter Scale Breeders' Cup Sprint Championship Handicap (gr. II) over Lion Tamer and Clock Stopper, plus the West Virginia Derby (gr. III) over Pollard's Vision. He also captured the Derby Trial Stakes (gr. III) at Churchill Downs in his fourth start and this year's seven-furlong Super Stakes in track-record time of 1:22.28 at Tampa Bay Downs.All four of Sir Shackleton's stakes-placings came in graded events in New York. In addition to his runner-up effort in the Woodward, Sir Shackleton was third to Ghostzapper in the Metropolitan Handicap (gr. I), and also placed in the Whitney Handicap (gr. I) and Dwyer Stakes (gr. II).Sir Shackleton, who was retired in March because of an injured sesamoid, exited racing with seven wins from 20 starts and earnings of $1,051,500 while trained by Nick Zito. He is out grade I stakes-placed Naskra Colors (by Star de Naskra) and will stand for $7,500.