Guide to USDA pain/distress categories
Animals being bred, conditioned, or held for future use. Example: breeding colonies, sentinel animals, animals awaiting assignment to a study.
Procedures involving no pain, or momentary/slight pain. Examples: routine blood draws, injections, gavage, euthanasia by approved methods, behavioral observation without intervention, non-invasive imaging under brief anesthesia.
Procedures that cause more than momentary pain or distress, where appropriate anesthesia, analgesia, or tranquilizers are used. Examples: survival surgery with post-operative analgesia, tumor implantation with pain management, chronic catheter placement.
Procedures causing pain or distress where pain-relieving drugs are withheld because they would compromise the study. This is the most scrutinized category. Examples: pain behavior studies (analgesics would eliminate the endpoint), certain addiction models, lethal dose studies where analgesics alter metabolism. Every Category E entry requires a written justification reviewed by the IACUC.