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Pain and Distress Categories

Designation of pain and distress categories for animal use protocols follows USDA classifications (B, C, D, E). Please consult the USDA Categories to identify the appropriate categories for common studies.

USDA Categories

Category B - No Experimental Manipulation

Animal holding or breeding when no procedures are performed. In practice this is rarely used, since genotyping or euthanasia of retired breeders are category C procedures.

Category C - No or Minimal Pain or Distress

Minimally invasive procedures that do not involve anesthesia, including routine injections (non-toxic, non-irritating), venipuncture, tail biopsy (preweaning), brief restraint, most behavioral studies. Also included is euthanasia after CO2 or anesthetic administration. Minor manipulation and minimally invasive procedures that are best accomplished with chemical restraint (i.e., sedative or anesthetic) to minimize distress or struggling, or to improve the technical aspects of the procedure, but are otherwise not necessarily considered to be painful. Examples would include the momentary use of isoflurane anesthesia in rodents for certain blood collection techniques or the use of anesthetics to produce temporary immobility for irradiation or imaging studies.

Category D - Painful/Stressful Procedures With Anesthesia or Analgesia

All survival and non-survival surgery, disease conditions with pain relief provided (e.g., arthritis treated with anti-inflammatory agents).

Category E - Painful/Stressful Procedures without Anesthesia or Analgesia

Requires scientific justification that anesthetics, analgesics or tranquilizers cannot be used without adversely affecting the study. Institutions must report all covered species used in Category E to the USDA, which issues an annual public report containing this information.

Last Published: Sep 30, 2016