| Name | Color | Sex | Year of birth | Microchip | Sire | Dam | Breed | Breeder |
|---|---|---|---|---|---|---|---|---|
| Uncle Storm | bay | c | 2023 | 981020051145228 | Uncle Chuck | Keep It Classic | Thoroughbred | River Oak Farm LLC |
| Uncle's Lassie | chestnut | f | 1916 | Planutess | Thoroughbred | USA | ||
| Uncommitted | bay | f | 1974 | Buckpasser | Lady Be Good | Thoroughbred | USA | |
| Unconquered | chestnut | f | 1983 | Groshawk | Turbulent Miss | Thoroughbred | USA | |
| Unconscious | c | 1968 | Prince Royal | Brown Berry | Thoroughbred | USA | ||
| Undeniably | chestnut | f | 1987 | In Reality | Past Forgetting | Thoroughbred | USA | |
| Under Canvas | f | 1943 | Winterhalter | Thoroughbred | ||||
| Under Oath | bay | f | 1986 | Deputed Testamony | China Bound | Thoroughbred | USA | |
| Under Tack | chestnut | c | 2012 | Fusaichi Pegasus | Wild Encounter | Thoroughbred | USA | |
| Under the Clock | f | 1950 | Thoroughbred | Great Britain |