The University of Iowa
Vertebrate Animal Research

Pain Recognition in Laboratory Animals (Informational Sheet)

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OAR Informational Sheet: Pain Recognition in Laboratory Animals

Informational Sheet: The IACUC has provided a set of guidance documents (Policies, Guidelines, and Informational Sheets) for use when planning animal procedures at the University of Iowa. Informational Sheets provide information about frequently asked questions and represents guidance for best practices. Deviation from the recommendation(s) does not require specific justification.

 

Purpose: The purpose of this document is to help researchers and OAR husbandry staff recognize signs of pain in animals.  This document does not list all signs of pain but rather lists more common and easy to identify signs of pain in animals. 

All investigators should consider that procedures that cause pain or distress in human beings may cause pain or distress in other animals.1 Procedures expected to cause more than slight or momentary pain (e.g., pain in excess of a needle prick or injection) require the appropriate use of pain-relieving measures unless scientifically justified in an approved animal care and use protocol.2

Relief of Pain

Details of recommended pain relief methods and doses can be found in the IACUC Analgesia Guidelines, including non-pharmacologic (non-drug) methods which should be considered in all cases of potentially painful procedures, including those for which analgesic drugs are contraindicated by study design.

  • Mice

    • Hunched posture
    • Reduced grooming and ruffled fur
    • Reduced level of spontaneous activity
    • Reduced food/water intake
    • Separation from cage mates
    • Squinty-eyes
    • Pale eyes (if albino)
    • Increased aggressiveness when handled

  • Rats

    • Hunched posture
    • Reduced grooming and ruffled fur
    • Reduced level of spontaneous activity
    • Falling/staggering, poor gait and twitching
    • Reduced food and water intake
    • Red-staining around nose and/or eyes (i.e. porphyrin secretions)
    • Squinty-eyes
    • Pale eyes (if albino)
    • Back arching behavior
    • Horizontal stretching behavior
    • Abdominal pressing behavior (briefly pressing abdomen to the ground)
    • Increased aggressiveness when handled

  • Rabbit

    • Decreased fecal production
    • Reduced food and/or water intake
    • Reduced activity
    • Hunched posture
    • Tensing of muscles (guarding)
    • Bruxism (grinding of teeth)
    • Reduced grooming
    • Squint-eyed
    • Pale eyes (if albino)
    • Aggressiveness

  • Farm animals (i.e., pigs, sheep, etc.)

    • Hunched posture
    • Separation from flock or herd
    • Lack of interest in surroundings
    • Decreased mentation (mental activity)
    • Decreased appetite
    • Bruxism (teeth grinding)
    • Drooping ears
    • Head drooping below withers
    • Vocalization
    • Grunting (spontaneously, or when painful region palpated)
    • Lameness
    • Long durations of lying down and reluctant to stand when prompted
    • Restlessness
    • Tachycardia (rapid resting heart rate)

  • Dog

    • Hunched posture with lowered head
    • Decreased or absent appetite
    • Decreased grooming
    • Licking wound or surgical site
    • Lameness
    • Guarding (protecting) the painful area
    • Stiff gait and slow to rise
    • Trembling or shaking
    • Limited or no movement when awake
    • Weak tail wag or low carriage of tail
    • Sitting or lying in an abnormal position
    • Praying position (i.e. front legs and head on floor, hindquarters in the air)
    • Lack of normal vocalization (no greeting bark or noise)
    • Whining, barking or growling
    • Dull mentation or agitation
    • Inappropriate urination or defecation, or not moving away from it
    • Acts out of character (gentle dogs may bite or become aggressive)

  • Cat

    • Hunched posture with lowered head
    • Decreased or absent appetite (associated with weight loss when chronic)
    • Decreased grooming
    • Licking wound or surgical site
    • Bearing no or partial weight on affected limb or any degree of limp
    • Guarding (protecting) the painful area
    • Sitting or lying in an abnormal position
    • Trembling or shaking
    • Limited or no movement when awake
    • Stiff gait and slow to rise
    • Lack of normal vocalization (no noise of greeting or wanting to be fed)
    • Yowling or crying (with acute pain)
    • Hissing or growling, especially when painful area is touched
    • Hyperventilation or open mouth breathing
    • Acts out of character (aggressive or playful cats may become docile or quiet)
    • Inappropriate urination or defecation, or not moving away from it
    • Dull mentation or agitation

  • Ferrets

    • Inappetance
    • Lameness
    • Reluctance to move
    • Trembling
    • Vocalization
    • Teeth grinding
    • Hunched
    • Lip licking
    • Repeated or excessive yawning

  • Guinea Pigs

    • Anorexia or inappetance
    • Lameness
    • Increased vocalization
    • Decreased activity
    • Decreased water consumption
    • Mutilation of painful area

  • Hamsters

    • Weight loss
    • Excessive scratching and licking
    • More aggressive when handled
    • Vocalization when handled
    • Mutilation of painful area

  • Birds and Poultry

    • Vocalization  
    • Crouched posture
    • Closed or partially closed eyes
    • Inappetence
    • Inactivity
    • Lameness
    • Reduced perching

  • Amphibians

    • Amphibian species such as frogs, toads, and salamanders are commonly used in laboratory animal research settings, but there is no objective means to assess the presence and severity of pain in amphibians, especially since they do not exhibit any facial expression. However, research studies have shown that amphibians are able and motivated to learn to avoid noxious stimuli.

      Some exotic animal clinicians use nonspecific clinical signs such as decrease in avoidance movement (e.g., when approached by a handler) or decrease in appetite as indicators of pain in these animals.4

  • Fish

    • It is difficult to determine the nature of the response to pain in fish or whether their experience is similar to that observed in mammals. Although there have been few species-specific studies, there is evidence that fish exhibit a pronounced initial response to injuries or to contact with nociceptive stimuli or chemical algesics but their response to chronic stimuli has not been characterized.

      Generally, fish react to noxious stimuli (such as puncture with a hypodermic needle) with strong muscular movements, and when exposed to a noxious environment (such as an acidic solution) show abnormal swimming behavior, attempts to jump from the water, and more rapid opercular movements. Such effects indicate some, perhaps considerable, distress, but it is not possible to describe the distress unequivocally as pain-induced.4


 

References

  1. U.S. Government Principles for the Utilization and Care of Vertebrate Animals Used in Testing, Research, and Training
  2. Pain and Distress in Laboratory Animals. ACLAM position statement approved October 29th, 2001.
  3. Guidelines for the Assessment and Management of Pain in Rodents and Rabbits ACLAM position statement approved July 2006.
  4. “Recognizing Pain in Animals” ILAR, <http://dels-old.nas.edu/animal_pain/>.  2009.

 

Last updated 09/08/2021