USDA Pain & Distress Categories
According to regulatory agencies, all vertebrate animals used in research, teaching or testing must be assigned to an appropriate pain category. The chart below outlines these categories and a few of the examples for each. If you are in doubt as to which category your animals may fall under, please contact the DLAR veterinarians. Please note there is no USDA Pain Category A.
|USDA Category B||USDA Category C||USDA Category D||USDA Category E|
|Breeding or Holding Colony Protocols||No more than momentary or slight pain or distress and no use of pain-relieving drugs, or no pain or distress. For example: euthanatized for tissues; just observed under normal conditions; positive reward projects; routine procedures; injections; and blood sampling.||Pain or distress appropriately relieved with anesthetics, analgesics, and/or tranquilizer drugs or other methods for relieving pain or distress.||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.|
A simple definition of a painful or distressful procedure on an animal in this:
"A procedure that would cause pain or distress in a human."
It is important to remember and understand that if an animal will need to undergo multiple procedures, it must be placed in the category indicated for the most painful/distressful procedure it will be experiencing. Also note that a single animal cannot be placed in multiple categories.
Pain categories are described as follows:
Category B animals are those that are being “bred”, conditioned, or held for use in teaching, testing, experiments, research, or surgery but not yet used for such purposes.” These animals have not been used for any research procedure, however minor. Category B is the place to put breeders and other animals that are not undergoing any experimental procedures.
Category C animals are not subjected to procedures that involve pain or distress or would require the use of pain-relieving drugs. Routine procedures such as injections and blood sampling from veins that produce only mild, transient pain or discomfort are reported in this category. Another example of Category C procedures is an observational study of animal behavior. Animals that are euthanized before tissue collection or other manipulations are also commonly placed in this category, if no other procedures performed that put them in a higher pain/distress category.
Category D animals are those subjected to potentially painful procedures for which anesthetics, analgesics, or tranquilizers will be used. The important concept is that animals are given appropriate anesthesia and/or pain relief to limit their pain and distress as much as possible.
Examples of category D procedures are
- Surgery conducted with appropriate anesthesia and postoperative analgesia;
- Rodent retro-orbital eye bleeding performed under anesthesia;
- Non-human primate tattooing performed for identification under anesthesia;
- Removal of small tumors under local or general anesthesia, and use of analgesia after an animal’s skin is exposed to ultraviolet light to cause a “sunburn”; and
- Terminal exsanguinations (euthanasia by removal of blood) under anesthesia
Category E animals are those that are subjected to painful or stressful procedures without the use of anesthetics, analgesics, or tranquilizers. Withholding of anesthetics, analgesics, or tranquilizers can only be allowed if it is scientifically justified in writing and approved by the IACUC. Examples of category E procedures are lethal dose studies (e.g. LD50 studies) that allow animals to die without intervention, pain studies that would not be possible if pain-relieving agents were administered, and psychological conditioning experiments that involve painful stimuli such as noxious electrical shock that cannot immediately be avoided by an animal.
By law, the institution must annually report all category E procedures to the USDA and include a scientific justification supporting the IACUC’s decision to approve them. It is important for the information on category E procedures to be complete and accurate1.
1. descriptive text from AALAS Learning Library Training Module.
Guidelines for determining USDA classification in protocols involving tissues 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.Guidelines for determining USDA classification in protocols involving tissue collection before/after euthanasia and/or animal perfusion:
- 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). In this scenario, it is necessary to justify why the animal couldn't 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 which require tissue manipulation or other prolonged techniques prior to the animals death (more than a few minutes) should be classified as non-survival surgery (USDA D). Similarly, if an animal will be anesthetized so that the tissue can be collected in the "freshest" possible state (i.e. heart) and the tissues will be rapidly excised, the procedure should be classified as euthanasia (USDA C). (Note: In this scenario, it is difficult to justify why the animal couldn't 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).
- 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 be perceiving. 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.