Clinical Signs of Pain and Disease in Laboratory Animals

    Revision Date: 
    August 11, 2021
    Responsible Official: 
    IACUC Chair
    Responsible Office: 
    Office of Animal Research Support (OARS)

    Guideline Sections

    4446.1 Background

    4446.2 Assessment of Pain, Distress and Discomfort in Mammals

    4446.3 Assessment of Disease in Mammals

    4446.4 Pain and Disease in Amphibians and Fish

    4446.1 Background

    Many species can mask clinical signs of pain, distress and disease, and signs can vary by species (with individual variation as well). Therefore, it is imperative to have an understanding of normal behavior for that species/animal and to closely observe for clinical signs and behaviors that may indicate pain or disease. The descriptions below describe species-specific clinical manifestations of pain and/or disease, though it is important to keep in mind that many of these signs are nonspecific or may occur due to general ill health. The presence of any of these clinical signs may be useful for determining pain categories and setting criteria for experimental and humane endpoints.

    4446.2 Assessment of Pain and Distress

    The following is a list of clinical signs and behaviors that may indicate pain:

    Rats and Mice*

    Sign or Behavior Comments
    Abnormal posture Hunched posture is a general sign of pain or disease
    Behavior changes during handling May be unusually aggressive or placid
    Changes in activity/mobility Decreased mobility may be localized to area of pain (e.g. limb) or may be generalized.  Rodents in pain generally have decreased activity, but increased activity may also be seen. Other abnormal behaviors include back-arching, belly-pressing, twitching, and staggering.
    Changes in facial expression Utilizing a grimace scale may be beneficial in identifying pain. See: https://nc3rs.org.uk/grimacescales#posters
    Decreased body temperature Animals that feel cold to the touch are likely severely hypothermic and may be moribund
    Decreased food and/or water intake May be associated with weight loss, dehydration, and decreased urine/fecal output.  Prolonged skin tent indicates dehydration.  Body condition scoring may be more useful than body weight in some circumstances. See: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2846001/
    Decreased grooming, piloerection Coat appears scruffy, hairs may be raised
    Decreased nest-building Particularly meaningful in mice, which have a strong drive to build nests
    Decreased response to external stimulation Attempts to escape when handled are normal in rodents unless well-habituated to handling – failure to exhibit this behavior may indicate pain or distress
    Licking, scratching at painful site May result in trauma or exacerbate lesion severity due to self-mutilation
    Pale mucous membranes/extremities Easiest to visualize by examining paws, tails, ears; can also look in mouth
    Porphyrin (red pigment) staining around eyes, nose, paws, forelimbs Generally pertains to rats
    Separation from group Mice & rats are social and normally rest in close proximity to one another during the day (are nocturnal)
    Shallow and/or rapid respirations Normal respiratory rate = 100-230 breaths per minute
    Squinting of eyes By itself this sign could indicate pain associated with ocular problem, but if combined with other signs, such as ear position, whisker change, nose bulge, it could also indicate an extra-ocular source of pain. See: https://nc3rs.org.uk/grimacescales#posters
    Teeth chattering, vocalization  

    *Although there is little information in the literature regarding specific signs of pain in other small rodents, use of the signs in the table above is recommended as a guideline for pain assessment; particularly: decreased activity, piloerection, ungroomed appearance, abnormal posture, and changes in respiration.

    Ground Squirrels

    Sign or Behavior Comments
    Changes in activity/mobility Looping the cage without stopping, sneezing
    Decreased food and/or water intake Reduced food and water intake is normal for pre-hibernation squirrels
    Decreased grooming, piloerection  
    Quiet, less alert  

    Guinea Pigs and Hamsters

    Sign or Behavior Comments
    Changes in activity/mobility  
    Decreased food and/or water intake This may exacerbate gut stasis that can occur post-operatively or secondary to pain
    Decreased grooming, piloerection  
    Hiding  
    Quiet, less alert Normal guinea pigs stampede and squeal when startled, when attempts are made to handle them, or when strangers are in the room; however, guinea pigs also tend to freeze in the presence of an observer, which makes assessment of attitude difficult
    Shallow and/or rapid respirations Normal respiratory rate = ~40-100 breaths per minute at rest
    Social behavior May show less interest in play or social interactions

    Rabbits

    Sign or Behavior Comments
    Abnormal posture With abdominal pain, may have arched back, contraction of the abdominal muscles, and abdominal pressing
    Behavior changes during handling May attempt to hide; reactions to handling may be exaggerated (e.g. rapid fits of locomotion); may vocalize if in acute pain
    Changes in activity/mobility Twitching, wincing, flinching may also be observed while at rest
    Changes in facial expression Utilizing a grimace scale may be beneficial in identifying pain. See: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0252417
    Decreased food and/or water intake This may exacerbate gut stasis that can occur post-operatively or secondary to pain.  May present as scant and/or small fecal pellets.
    Decreased grooming  
    Hiding  
    Localized licking, biting, scratching May be associated with localized pain
    Quiet, less alert  
    Shallow and/or rapid respirations; may also have slow, deep respirations with nasal flaring Normal respiratory rate = 30-60 breaths per minute at rest
    Teeth grinding May occur but is not completely reliable as a behavioral indicator
    Vocalization  

    Dogs

    Sign or Behavior Comments
    Abnormal posture or gait  
    Behavior changes during handling May be unusually apprehensive or aggressive; may show less interest (e.g. decreased tail wagging) towards familiar handlers
    Changes in activity/mobility Dogs in pain may move stiffly or be unwilling to move.  If pain is less severe, the animal may be restless and more alert.  Localized pain to the limbs may cause limping or holding up the limb.
    Decreased food and/or water intake  
    Localized licking, biting, scratching May be associated with localized pain
    Quiet, less alert  
    Shallow and/or rapid respirations Normal respiratory rate = 10-35 breaths per minute at rest
    Shivering  
    Social behavior May show less interest in play or social interactions
    Vocalization Spontaneous barking is unlikely; more likely to whimper or howl; may growl without apparent provocation (note that lack of vocalization is not a reliable indicator of pain level)

    Ferrets

    Sign or Behavior Comments
    Abnormal posture or gait May crouch/hunch in response to abdominothoracic pain; may extend head/neck/body with thoracic pain; may stand or lie on its side with its back arched or walk with a stilted gait with abdominal or back pain
    Behavior changes during handling May be unusually aggressive or attempt to escape
    Changes in activity/mobility Localized pain to the limbs may cause limping or holding up the limb
    Decreased food and/or water intake  
    Hiding  
    Localized licking May be associated with localized pain
    Quiet, less alert  
    Shallow and/or rapid respirations Normal respiratory rate = 20-40 breaths per minute at rest
    Social behavior May show less interest in play or social interactions and/or may separate from the group
    Vocalization May cry, yowl, growl or hiss in response to handlers

    Sheep and Goats

    Sign or Behavior Comments
    Abnormal posture May be holding head low; may change posture frequently
    Behavior changes during handling May stamp feet and otherwise appear agitated
    Changes in activity/mobility General reluctance to move
    Decreased food and/or water intake May be associated with decreased or cessation of rumen activity; weight loss may occur
    Localized licking or kicking May be associated with localized pain
    Quiet, less alert May appear dull and depressed, show little interest in surroundings
    Shallow and/or rapid respirations Normal respiratory rate =10-30 breaths per minute at rest
    Teeth grinding  
    Vocalization  

    Pigs

    Sign or Behavior Comments
    Behavior changes during handling Squealing/attempting to escape may become more pronounced than usual; can become aggressive; may be less responsive to familiar handlers
    Changes in activity/mobility General reluctance to move; may be restless
    Decreased food and/or water intake  
    Hiding  
    Quiet, less alert  
    Shallow and/or rapid respirations Normal respiratory rate = 17-23 breaths per minute at rest
    Social behavior May show less interest in social interactions with humans and/or conspecifics
    Teeth grinding  
    Vocalization May become more pronounced

    Birds

    Sign or Behavior Comments
    Abnormal posture Crouched posture with closed eyes and head drawn towards body in chronic states of pain; neck may be retracted; ruffled feathers or “puffed up” appearance
    Behavior changes during handling Escape reactions enhanced or dulled; small species struggle less and emit fewer distress calls than large species
    Changes in activity/mobility May show excessive movement; head movements increase in extent and frequency; immobility may occur in response to chronic pain; localized pain to a limb may cause decreased use or holding limb close to body; standing on one leg, shifting leg lameness, standing on metatarsus, or resting on sternum
    Reduced perching May be found at bottom of the cage
    Shallow and/or rapid respirations  
    Vocalization Decreased or abnormal vocalization

    4446.3 Assessment for Disease in Mammals

    Specific clinical signs of disease are dependent upon the system that’s affected and may or may not be associated with pain. The following list provides examples of clinical signs that may be seen when disease affects specific body systems.

    System Clinical signs that may be observed
    Respiratory Altered respiratory depth, rate, and effort; pale or cyanotic mucous membranes, open-mouth breathing
    Urinary Increased or decreased urine production; increased water intake; dehydration; weight loss; penile prolapse; urinary obstruction (enlarged bladder) secondary to fight wounds affecting genitalia in males; blood in urine
    Gastrointestinal Diarrhea or soft stool with or without blood; prolapsed rectum; weight loss; dehydration; (note: rodents cannot vomit)
    Nervous Depression/severe lethargy, seizures; autophagia; ataxia; paralysis; decrease in mentation
    Cardiovascular Increased respiratory rate; coughing; exercise intolerance; peripheral edema; pale or cyanotic mucous membranes; lethargy; weight loss
    Musculoskeletal Lameness; swelling; biting/scratching at affected area; muscle atrophy if chronic
    Immune Nonspecific signs of illness due to secondary infection; enlarged lymph nodes; abscessation
    Reproductive Females: vaginal/uterine prolapse; discharge; difficulty giving birth Males: penile/preputial trauma (due to fighting); penile prolapse
    Integumentary Ulceration (e.g. ulcerative dermatitis); fight wounds (usually found on the hind end and genitalia in males); pustules; abscesses; necrotic tissue; unkempt coat due to decreased grooming
    Non-specific signs of illness Unkempt coat; hunched posture; dehydration; decreased food/water intake; inactivity; decreased nest-building (mice); porphyrin staining around eyes, nose, etc. (rats) 

    4446.4 Pain and Disease in Reptiles, Amphibians and Fish

    The topic of pain in reptiles, amphibians and fish is controversial; these species demonstrate avoidance behavior in response to noxious stimuli, but whether this is truly considered pain is widely debated. Therefore, for these animals, a general assessment of health should be made if there are any concerns regarding potential pain, distress or disease. The following list provides examples of clinical signs that may be seen in these animals.

    Reptiles

    System Clinical signs that may be observed
    Behavior changes during handling May attempt to bite
    Decreased food and/or water intake May be associated with weight loss
    Flinching and muscle contractions  
    Quiet, less alert  

    Amphibians

    System Clinical signs that may be observed
    Gastrointestinal Increased or decreased defecation; regurgitation of stomach contents; decreased food intake
    Integumentary Changes in skin color, skin sloughing, white film on skin
    Whole body Weight gain or bloating; weight loss or thin body condition
    Behavioral Buoyancy problems, floating on water’s surface, reluctant to dive, turning outward of front limbs, swimming with a whole body tilt, swimming upside down or in circle, lack of avoidance behavior (e.g. to handlers)

    Fish

    System Clinical signs that may be observed
    Gastrointestinal Decreased food intake
    Integumentary Fin abnormalities; white film on scales; missing scales; skin/scale discoloration; ulceration; raised scales
    Whole body Enlarged abdomen/bloating
    Ocular Clouded eyes; protruding eyes
    Behavioral Lethargy, swimming sideways, staying at the bottom of the tank, rubbing against surfaces, gasping at water’s surface; separation from others (schooling fish such as zebrafish); quick twisting swimming motion (“flashing”)

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