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
4446.2 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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