| Registered Name | Owner / Club | Status |
|---|---|---|
| Oreo Speedwagon | Suzy Davis Warrington | Approved |
| Orfan Annie | Anne O' Riordan Knocknamana Country | Approved |
| Oriens Star | Ashling O'Brien Barrow Valley | Approved |
| Orioles Rain | Elizabeth O' Connell Highland Lodge | Approved |
| Orlando (KWPN) | Owen Smyth Twinfort | Approved |
| Orlando of Araglen | Grainne Healy Kilrainy | Approved |
| Orlas Cobra | Aiden Fogarty Rock of Cashel | Approved |
| Orman (KWPN) | Grainne Alexander Greenhills | Approved |
| Orotika | Eamon Briscoe Castle Hill | Approved |
| Orphen Lux | Kate Moran Arderin | Approved |
| Oscar | Sadb Waldron Nuenna Farm | Approved |
| Oscar (IPSA) | Katherine O'Brien Benbulben | Approved |
| Oscar Bui | Elizabeth Maher Killcarrick | Approved |
| Oscar Duke | Des Farrell Killarney | Approved |
| Oscar Encore (IRE) | Laura Tierney Killossery | Approved |