| Abbreviation | Definition |
|---|---|
| OCAS | Orange County Animal Services |
| ODCE | Optimum Design of Crossbreeding Experiments (genetics) |
| OFA | Orthapedic Foundation for Animals |
| OFA | Orthopedic Foundation of Animals |
| OHAR | Oak Hill Animal Rescue |
| OIE | World Organisation for Animal Health |
| OJAS | Open Journal of Animal Sciences |
| OLAM | Office of Laboratory Animal Medicine |
| OPAS | Ouachita Parish Animal Shelter |
| OPGA | Olympic Pygmy Goat Association |
| ORCA | Organization For Respect Compassion For Animals |
| ORCA | Organization For Responsible Care Of Animals |
| OSAC | Ocean State Animal Coalition |
| OSCAR | Offering Subsidized Care for Animal Recovery |
| OSPCA | Oahu Society for the Prevention of Cruelty to Animals |
| OTHA | Other Than Human Animal |
| PAACO | Professional Animal Auditor Certification Organization |
| PAC | People Animal Connection |
| PACC | Pima Animal Care Center |
| PACK | People and Animal Cardio Klub |