Procedures with animals that may cause more than momentary or slight pain or distress should be performed with appropriate sedation, analgesia, or anesthesia. Surgical or other painful procedures should not be performed on unanesthetized animals paralyzed by chemical agents [Principle V].

The AWRs, PHS Policy, and the Guide require the IACUC to ensure that animal-use protocols include strategies for minimizing pain and distress in animals. Specifically, USDA (through the AWR 2.31 (d)(ii) and (e) and APHIS/AC Policy 12) requires the investigator to consider alternatives to procedures that

TABLE 2-1 Indicators of Pain in Several Common Laboratory Animalsa


General Behavior




Decreased activity; excessive licking and scratching; self-mutilation; may be unusually aggressive; abnormal locomotion (stumbling, falling); writhing; does not make nest; hiding

Piloerection; rough/stained haircoat; abnormal stance or arched back; porphyrin staining (rats)

Rapid, shallow respiration; decreased food/water consumption; tremors


Head pressing; teeth grinding; may become more aggressive; increased vocalizations; excessive licking and scratching; reluctant to locomote

Excessive salivation; hunched posture

Rapid, shallow respiration; decreased food/water consumption


Excessive licking; increased aggression; increased vocalizations, inclusive of whimpering, howling, and growling; excessive licking and scratching; self-mutilation

Stiff body movements; reluctant to move; trembling; guarding

Decreased food/water consumption; increased respiration rate/panting


Hiding; increased vocalizations, inclusive of growling and hissing; excessive licking; increased aggression

Stiff body movements; reluctant to move; haircoat appear rough, ungroomed; hunched posture; irritable tail twitching; flattened ears

Decreased food/water consumption

Nonhuman Primate

Increased aggression or depression; self-mutilation; often a dramatic change in routine behavior (e.g., locomotion is decreased); rubbing or picking at painful location

Stiff body movements; reluctant to move; huddled body posture

Decreased food/water consumption

aNo single observation is sufficiently reliable to indicate pain; rather several signs, taken in the context of the animal’s situation, should be evaluated. The signs of pain may vary with the type of procedure (e.g., orthopedic versus abdominal pain).

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement