Categorizing the Pain and Distress of Procedures


Pain: "An unpleasant sensory and emotional experience associated with actual or potential tissue damage."3

Distress: "A state in which an animal cannot escape from or adapt to the external or internal stressors or conditions that it experiences resulting in negative effects upon its well-being."2

The USDA Animal Care Policy Manual defines painful or distressing procedures as "any procedure that would reasonably be expected to cause more than slight or momentary pain or distress in a human being to which that procedure is applied."5   Wayne State, like many institutions, has extrapolated USDA categories to cover all species on campus.


USDA Pain and Distress Categories

USDA CATEGORY B:  Animals being bred, conditioned, or held for use in teaching, testing, experiments, or research, but not yet used for such purposes. 

USDA CATEGORY C:  Animals used in teaching, research, experiments, or tests that involve no pain or distress, or only momentary or slight pain or distress that WOULD NOT REQUIRE anesthetic, analgesic or tranquilizing agents.

USDA CATEGORY D:  Animals used in teaching, research, experiments, or tests where appropriate anesthetic, analgesic, or tranquilizing agents ARE USED to avoid pain or distress.

Animals used in research, experiments, or tests that may cause pain or distress that cannot be treated with an anesthetic, analgesic or tranquilizer, if the agent or procedure producing the pain/distress is immediately discontinued or the animal is euthanized to prevent pain and/or suffering.

USDA CATEGORY E:  Animals used in teaching, research, experiments, or tests involving pain or distress to the animals and for which the use of appropriate anesthetic, analgesic, or tranquilizing drugs will adversely affect the procedures, results, or interpretation of the teaching, research, experiments, surgery, or tests. IF ANIMALS ARE LISTED IN THIS CATEGORY, DETAILED JUSTIFICATION MUST BE PROVIDED IN THE PROTOCOL APPLICATION.


Classification of Common Procedures

Category B

Category C

Category D

Category E

  1. Animals used for breeding to maintain the colony
  2. Offspring of improper genotype or sex
  3. Any animal not used for teaching, testing, or research purposes
  1. Momentary physical restraint
  2. Weighing animals
  3. Observation of animal behavior
  4. Blood collection*
  5. Compound or cell administration (SC, PO (gavage or self-administration), IP, IV, IM, or ID)
  6. Rodent tail tip sampling (< 21 d age)
  7. Percutaneous catheter implantation
  8. Animal identification (ear notch, ear tag, microchip, sharpie pens, tattoos)
  9. Post-mortem tissue harvest
  10. Training using positive reinforcement
  11. Induction of tumors or spontaneous tumor models that do not cause detectable adverse effects
  1. Blood collection (RO or IC)
  2. Compound or cell administration (RO or IC)
  3. Tissue or organ collection under anesthesia
  4. Exsanguination under anesthesia
  5. Terminal surgical procedure
  6. Survival surgical procedure using appropriate anesthetic and analgesic agents
  7. Non-invasive imaging of animals (X-ray, CT, SPECT/CT, PET, MRI, US, Bioluminescence, Fluorescence) with appropriate sedation/anesthesia
  8. Use of a therapeutic agent to treat an induced or heritable disease process
  9. Induction of diabetes which is controlled with insulin or equivalent treatments
  1. Animal identification (rodent toe clipping)
  2. Prolonged restraint
  3. Prolonged fastinga or food/fluid restriction
  4. Survival surgical procedures where analgesics cannot be administered
  5. Studies with death as an endpoint
  6. Exposure to abnormal or extreme environmental conditions
  7. Experimental autoimmune encephalomyelitis models (EAE)
  8. Models that induce paralysis or immobility
  9. Untreated diabetes models
  10. Tumor models that cause adverse effects including ulceration, necrosis
  11. Systemic or metastatic tumor models
  12. Housing mice in metabolic or wire-bottom caging
  13. Behavioral tests (Forced swim or exercise, fear conditioning, tail suspension, resident-intruder, inescapable electric shock)
  14. Toxicological or untreated infectious disease models that result in clinical signs or death
  15. Breeding of animals with a hereditable phenotype that results in morbidity or early mortality
  16. Traumatic brain injury (TBI), stroke, or shock models

SC, subcutaneous; PO, per os (oral); IP, intraperitoneal; IV, intravenous; IM, intramuscular; ID, intradermal; RO, retro-orbital; IC, intracardiac; CT, computer tomography, SPECT/CT, single photon emission computer tomography; PET, positron emission tomograph; MRI, magnetic resonance imaging; US, ultrasound;

*Within Blood Collection: Maximum Volumes and Fluid Replacement guideline limits of total volume and frequency

aFasting of food/fluid beyond that which is necessary for surgery



  1. European Commission. (2009). Expert Working Group on Severity Classification of Scientific Procedures Performed on Animals: Final Report.
  2. National Research Council (2000). Definition of Pain and Distress and Reporting Requirements for Laboratory Animals: Proceedings of the Workshop Held June 22, 2000. Washington, DC: The National Academies Press.
  3. National Research Council (2009). Recognition and Alleviation of Pain in Laboratory Animals. Washington, DC: The National Academies Press.
  4. National Research Council (2011). Guide for the Care and Use of Laboratory Animals, 8th Ed. Washington, DC: The National Academies Press.
  5. NIH Animal Research Advisory Committee Guidelines. (2020). Preparing USDA Annual Reports and Assigning USDA Reporting Columns.
  6. NIH Animal Research Advisory Committee Guidelines. (2020). Guidelines for Pain and Distress in Laboratory Animals: Responsibilities, Recognition, and Intervention.
  7. USDA APHIS (2011). Animal Care Resource Guide. Policy 11 Painful and Distressful Procedures.
  8. USDA APHIS (2020). Animal Welfare Act and Regulations.