The 4-year-old filly finished 2009 with a record of eight wins from eight starts, including a 20-lengths victory in the Kentucky Oaks and historic victories against males in the Preakness Stakes, the Haskell Invitational and the Woodward.
The unbeaten skein was enough to decisively defeat Breeders' Cup Classic winner Zenyatta in the Horse of the Year balloting.
This year, however, the Medaglia d'Oro filly had not been the same, finishing second twice before posting two unspectacular wins. Her last race, the Personal Ensign at Saratoga Aug. 29, was a test to see if she could get 1 1/4 miles -- the distance of the Breeders' Cup Classic. She could not, fading in the stretch to lose by a length to Persistently.
"Rachel Alexandra did not return to her 2009 form," owner Jess Jackson said Tuesday. "I believe it's time to retire our champion and reward her with a less stressful life."
Jackson said Rachel Alexandra will be bred to Curlin, who preceded her as Horse of the Year.
In an irony of timing, Persistently's trainer, Shug McGaughey, was asked about Rachel Alexandra during a media teleconference Tuesday morning.
"She had a tough campaign as a 3-year-old," McGaughey said. "Did it take a little bit out of her? Maybe it did. But she's still a fabulous filly."