IACUC Guideline: Determination of Levels of Pain and Distress
USDA Pain Levels:
Level B: Breeding or Holding Colony Protocols
Level C: No more than momentary or slight pain or distress. For example: euthanatized for tissues; just observed under normal conditions; positive reward projects.
Level D: Pain or distress relieved with anesthetics, analgesics and/or tranquilizer drugs or other methods for relieving pain or distress. For example: survival surgery, non-survival surgery, induced infections or antibody production with appropriate anesthesia and post-op/post-procedure analgesia when necessary.
Level E: Pain or distress or potential pain or distress that is not relieved with anesthetics, analgesics and/or tranquilizer drugs or other methods for relieving pain or distress.
(Note: there is no USDA level A.)
Examples: For determining USDA classification in protocols involving tissue collection before/after euthanasia and/or animal perfusion:
- If an animal will be euthanatized by an approved physical or chemical method of euthanasia solely for the collection of tissues (after the animal's death), the procedure should be classified as USDA C.
- If an animal will be anesthetized so that the tissue can be rapidly excised and collected (i.e. eye, heart) the procedure should be classified as euthanasia, USDA C. (Note: In this scenario, it is difficult to justify why the animal could not be euthanatized rather than anesthetized.)
- If an animal will be anesthetized so that it can be chemically perfused, the same "test of time" applies (i.e. long, technical manipulations should be classified as USDA D, while rapid intravascular injection of the perfusate without other manipulations should be classified as USDA C).
- If an animal will be anesthetized so that non-vital tissues can be collected (liver or skin biopsy), and the animal will then be allowed to recover, the procedure should be classified as USDA D (survival surgery).
- If an animal will be anesthetized so that non-vital tissues can be collected (liver or skin biopsy, etc.), and the animal will then be euthanatized, the procedure should be classified as USDA D (non-survival surgery). Note: In this scenario, it is necessary to justify why the animal could not be euthanatized (USDA category C) rather than anesthetized.
- If an animal will be anesthetized so that vital tissues can be collected (heart, both kidneys or lungs, whole liver, etc.), the animal will obviously succumb to the procedure. To determine whether this will be euthanasia or non-survival surgery, we must consider the definition of euthanasia. A critical component of this definition is "rapid unconsciousness followed by loss of cardiac, respiratory and brain function". Based on this definition, procedures that require tissue manipulation or other prolonged techniques prior to the animal’s death (more than a few minutes) should be classified as non-survival surgery (USDA D).
NOTE: Because the USDA classification system is based on the "potential for pain, distress or discomfort," the anesthetic/euthanasia drug dose becomes a critical concern. For example, if a known "euthanasia dose" of pentobarbital will be administered, drug irreversibility is assumed. Thus, once the animal is confirmed to be in an anesthetic plane (toe pinch response, etc.), tissues can be collected/ procedures can be performed without the concern about what the animal will perceive. This procedure would then be classified as USDA C. The Committee recommends using a euthanizing dose whenever possible. Other methods may be appropriate with proper scientific justification.
Reference: AVMA Guidelines on Euthanasia, 2007. http://www.avma.org/issues/animal_welfare/euthanasia.pdf
Accepted by the IACUC: 04-17-07; Revised and Reapproved July 2011