| Registered Name | Owner / Club | Status |
|---|---|---|
| Once Upon A Dream | Adrian Sweeney Nephin | Approved |
| One Cool Poet (IRE) | Blair Colton Killcarrick | Approved |
| One For The Yrad (GB) | Sean Shields Moyglare | Approved |
| One Hundred Percent | Marie Withers North Cork | Approved |
| One In A Million | Caitriona Harrison Mosstown | Approved |
| One Kamula | Darielle O'Sullivan Abbeylands | Approved |
| One of the Twins | Geraldine McGuinness Winterdown | Approved |
| One Station Diamond | Susan Humphreys Clonlara | Approved |
| One Step Ahead | Alanna Macey Hogan Mullingar | Approved |
| Only George | Daphne Scholts Cill Dara | Approved |
| Only Milo | Sandra Barnwell Clonshire | Approved |
| Only One Kanobie | Maria Howard Cheval | Approved |
| Only Otto | Sandra Barnwell Clonshire | Approved |
| Ooh Seamus | Rebekah Power Thomastown and District | Approved |
| Oonagh 55 | Kim McInerney Headfort | Approved |