Species-Specific Assessment of Pain in Laboratory
Animals
KAREN L. STASIAK, MSN, DVM,1* DON MAUL, MS, DVM,2 ELISA FRENCH, BS, LATG,2
PETER W. HELLYER, DVM, MS, DACVA,3 AND SUE VANDEWOUDE, DVM1
Pain has been defined by the International Association for the Study of Pain as “an unpleasant sensory and emotional experience
associated with actual or potential damage or described in terms of such damage”. However, the ability to describe the concept of
pain is difficult largely because pain is an individualized and subjective experience. What one person finds painful, another may
not; what relieves pain for one may not do so for another. Awareness of pain management has become an important health issue for
humans and animals. To effectively manage pain, it is crucial to be able to identify it, and identification of pain in animals can be
especially problematic. Recognition and alleviation of pain in animals used in biomedical research and teaching is an important
goal, both from a humane and regulatory perspective. This paper will: 1) review current literature regarding pain assessment using
pain scales and 2) describe how an institutional care and use committee (IACUC) has implemented an effective pain scoring system
to allow for an objective, accurate, and humane assessment of pain experienced by animals used in biomedical research.
Physiology of Pain
Indications for Managing Pain
Pain may be physiologic, pathologic, or neurogenic; acute or
chronic; visceral or somatic. Different types of pain require different interventions. Physiologic pain starts with highly
specialized receptors in the skin that sense changes in heat,
pressure, and chemical stimuli. These activated nociceptors
send their information to the spinal cord via two different afferent fibers: rapid, myelinated A-delta fibers, and slower,
unmyelinated C-fibers. In the spinal cord, the afferent nerve
fibers release neurotransmitters that allow different physiologic
responses to the painful stimuli. One response is the reflex arc,
which allows the body to rapidly withdraw from noxious stimuli.
Another is the transmission of information to the brain. There
are numerous spinal tracts for carrying nociceptive information
ultimately to the cerebral cortex, limbic system, and reticular
activating system. The processing of nociceptive information by
the brain allows for the perception of pain, emotional experience of pain, and the autonomic changes associated with pain
(1). This type of pain is physiologic in that it allows the body to
be protected from its environment. Pain becomes pathologic
when it is associated with tissue injury and is usually the result of
inflammation. Persistent pathologic pain can result in the “wind
up” phenomenon wherein the nervous system becomes overly
sensitized to any stimulation. Neurogenic pain occurs when there
is no obvious explanation for the sensation, such as “phantom
limb” pain that occurs after amputation of a limb (2).
Acute pain is from a known cause, such as injury or surgery,
and has a predictable course and duration (2). This type of pain
usually is amenable to analgesia (3). Chronic pain occurs when
pain is ongoing and is associated with a physiologic adaptation
to the sensation of pain. Therefore, measurable physiologic
changes that occur with pain are not always evident and one
must rely more on subtle behavioral cues (1, 4). Chronic pain
may be challenging to manage because the inciting cause may
not be evident.
Visceral pain refers to pain that arises from the viscera in the
abdominal or thoracic cavity. Somatic pain refers to pain arising
from the periphery, such as muscle or skin (2). These two different types of pain may respond differently to analgesia.
There are several reasons to advocate for pain management
in laboratory animals. First is the moral and ethical obligation to
relieve pain in animals. In 1998, the position paper from the
American College of Veterinary Anesthesiologists asserted that
there are no beneficial effects of unrelieved pain in animals and
that it is part of the veterinary oath to relieve animal suffering (3).
Second, it is the duty of the institutions governed by the Animal Welfare Act to follow established guidelines set forth, wherein
any animal subjected to a procedure that may cause more than
only momentary pain will receive appropriate sedation, analgesia, or anesthetics, unless such intervention would interfere with
the research outcome (5). The full Institutional Animal Care
and Use Committee (IACUC) must review any protocol that will
not use analgesics when indicated.
Third is to limit the effects of pain on research outcomes. The
body’s response to any stress, including pain, is complex, resulting in adaptive changes that may affect anatomical, physiological,
biochemical, immunological, and behavioral mechanisms (6).
Activation of the stress response may impact cardiovascular, respiratory, and gastrointestinal functions (1), as well as lead to the
development of a catabolic state (2). In 1994, Herzberg concluded that chronic pain had an affect on the immune system in
rats by decreasing antibody production (7). Unmanaged pain
may also result in changes in normal behaviors such as grooming, food and water intake, and reproduction.
Alleviation of distress in laboratory animals also should be considered. According to United States Department of Agriculture
guidelines “distress is a state in which an animal cannot escape
from or adapt to the internal or external stressors or conditions it
experiences, resulting in negative effects on its well-being” (8).
Unmanaged pain may lead to distress. There are many factors
that may contribute to distress including systemic illnesses, procedures, transportation, handling, and specific husbandry
practices (1, 9). Interventions to control these factors will limit
the effects of pain and distress on the animals’ well-being and
on research outcomes (10).
Colorado State University, Department of Pathology,1 Laboratory Animal Resources,2 Department of Clinical Science,3 Veterinary Teaching Hospital, Fort Collins, CO 80523-1682
*
Corresponding author
Volume 42, No. 4 / July 2003
Pain Scale Development
Identification of pain is crucial to knowing when to intervene
and whether the intervention has been successful in alleviating
discomfort. Elliot et al. (11) evaluated chronic pain measurements in human adults with the hopes of developing a standard
CONTEMPORARY TOPICS © 2003 by the American Association for Laboratory Animal Science
13
method of measuring changes. The subjects were given two different pain scoring tools. The first tool classified the extent of
the intensity of pain and resulting disability, and the second tool
was a retrospective assessment of how their pain had changed
over time. No correlation was found between classification of
their pain and the retrospective analysis. This finding underscores
the difficulty in accurately and consistently evaluating pain. Despite the difficulty in quantifying pain in humans, analgesia is
not routinely withheld (12).
Evaluation of pain in human neonates is only now emerging
as an important issue. Prior to the early 1990s, it was quite common for neonates to not receive any pain medications for invasive
procedures, including surgery. The prevailing thought at that
time was that the neonatal neurological system was not sufficiently
developed to feel pain. This belief has since been dispelled (13),
resulting in the development of neonatal pain assessment tools.
Evaluating pain in the human neonate is similar to pain evaluation in animals, in that the inability to articulate is a huge obstacle.
Soetenga et al. (14) described the assessment of the validity and
reliability of the pain scale developed for preverbal and nonverbal children. Their pain scale was composed of both physiologic
and behavioral indicators. The physiologic indicators included
heart rate, respiratory rate, blood pressure, and oxygen saturation, which are associated mostly with acute pain and lose
usefulness in evaluation of chronic pain. The behavioral indicators included facial expressions, crying, body movements, sleep
patterns, and consolability. The researchers concluded that this
type of pain scale has validity, inter-rater reliability, and internal
consistency. These are important concepts in developing a pain
scale for evaluation of pain in animals.
Confirming the validity of a pain scale ensures the accuracy of
the measured variables. The inter-rater reliability implies that two
independent raters, using the same scale at the same time, will
obtain the same score. The internal consistency ensures that all
subparts of the scale are measuring the same characteristic. Payen
et al. (15) had success in concluding that pain scales using behavioral indicators only can be a reliable and valid measure of
pain in critically ill, sedated adults. Berde and Sethna (16) reviewed
the developmental issues of pain assessment and management in
neonates and children. Children’s hospitals have commonly used
visual analogue pain scales, comprised of faces or drawings to
show degree of discomfort, and color analogue scales, in which
the increasing intensity of red shows increasing pain. Both behavioral and physiologic parameters to assess pain are used in
preverbal, nonverbal, and verbal children with success.
There have been attempts to develop pain scales for use in
animals. Liles and Flecknell (17) evaluated locomotor activity,
food and water consumption, and body weight after surgery in
rats. They concluded that postoperative analgesia reduced the
degree of decreased food and water consumption and loss of
body weight. The effects on locomotor activity were not as clear.
Therefore, the authors recommended monitoring food and
water consumption and body weight to evaluate the effectiveness of postoperative analgesia. One confounder, however, was
the identification that opioid analgesia could decrease food and
water intake in rats that did not undergo surgery. Likewise, rats
that received buprenorphine demonstrated pica leading to gastric distension (18), which may lead to increased pain or
decreased feed intake.
Morton and Griffiths (12) developed a table of species-specific indicators of pain. These investigators focused primarily on
posture, vocalizing, temperament, and locomotion. They also
identified changes in body systems such as cardiovascular, respiratory, digestive, nervous, and musculoskeletal responses to pain.
Sanford et al. (6) listed guidelines to assist in the assessment of
pain. Among the guidelines were clinical examination; physiologic
parameters; biochemical changes (specifically adrenocorticotro14
CONTEMPORARY TOPICS © 2003 by the American Association for Laboratory Animal Science
pic hormone and various adrenocortical hormones); mental status; abnormal activity (such as bruxism, kicking of the abdomen,
and altered sleep/wake cycles); posture changes; gait abnormalities; facial expressions; vocalizations; reluctance to be handled;
and response to analgesics. They also listed species-specific signs
that may be helpful in identifying pain.
The challenge in developing pain scales for use in animals is
that it requires detailed knowledge of many different speciesspecific behaviors. Prey species, such as ruminants, often hide
their pain so as not to become a target of predators. Likewise,
birds often display only subtle signs, such as ruffled feathers and
increased respiratory rate. There may also be variations within a
species, such as pain behaviors seen with different breeds of dogs
(19). In addition, some animals respond to pain with a fight-orflight response, whereas others may become immobile. The lack
of outward signs that we would recognize as pain does not imply
that pain does not exist. Table 1 summarizes selected articles
that have used pain scales for assessment in animals. A wide variety of behavioral and physiologic parameters are evaluated. Food
and water intake and body weight seem most consistently altered
by painful stimuli across species. Other parameters seem less
consistent and subject to observer bias.
Another difficulty in assessing pain in animals is the risk of
anthropomorphizing (6, 9). Although it may seem intuitive to
assume that what may cause pain in humans may also cause pain
in animals because of the similarities of the anatomic and chemical pathways, this approach may lead to a subjective, inconsistent
evaluation and treatment of pain in light of the differences between species (12, 20).
It should also be noted that there are differences between pain
assessment and analgesiometry in animals. Pain assessment for
the purpose of alleviating pain is focused on natural behaviors
in response to painful stimuli (i.e., surgery). Analgesiometry is
used for evaluation of analgesic effectiveness. It uses mechanical, thermal, electrical, or chemical stimuli to induce a
nociceptive response and evaluates an animal’s threshold to the
stimuli under the influence of various analgesics and doses.
Analgesiometry is coupled with an observed motor response so
that sedation or an underlying motor deficit is not responsible
for the increased nociceptive threshold identified (19, 21)
Application of Pain Scales
During the last two decades, the Colorado State University Institutional Animal Care and Use Committee (CSU IACUC) has
instituted several mechanisms to assure maximal alleviation of pain
and distress for animals used in biomedical research. Some of these
measures include: 1. requiring 3 days of postoperative analgesia
for major surgical procedures unless scientifically justified; 2. requiring use of pre-emptive as well as postoperative analgesics; 3.
recommending use of local anesthetics as an adjunct to pain control when appropriate; 4. including a board-certified veterinary
anesthesiologist as a standing member of the committee; and 5.
requiring personnel performing surgery to complete a training
course prior to being permitted to perform surgery. These actions
greatly improved management of acute pain in laboratory animals.
To address the issue of unalleviated acute pain or long-term/
chronic pain, the CSU IACUC appointed a ‘chronic pain subcommittee’ to evaluate current literature for methods and criteria that
could be used to more completely assess pain in laboratory animals. One of the central recommendations of this committee was
to evaluate postprocedural pain and distress more objectively by
way of using pain-scoring paradigms.
Consequently, the CSU animal use protocol form was modified to suggest a pain score be used as an objective measure of
pain experienced by animals undergoing an experimental procedure in order to encourage use and development of these tools.
Volume 42, No. 4 / July 2003
Table 1. Summary of selected articles using pain scales in animals
Species
Quality of pain
Year, study
Rat
Visceral
(intestinal
resection)
2001, Gillingham, Posture
et al. (25)
-stance
-locomotion
Physical condition
-haircoat
-nasal drainage
-ocular squinting
-porphyrin staining
Behavior
-activity
-temperament
Acute, surgical
(laparotomy)
2000, Rougham
and Flecknell
(26)
Rat
Behavioral
criteria evaluated
Physiologic
criteria evaluated
Conclusion of
parameter usefulness
Analgesia
evaluated
Analgesia
evaluated beneficial?
None
Based on previous
observations of behaviors
in postoperative rats,
these parameters are
consistent with others’
descriptions of
pain-related behaviors
Buprenorphine
Ineffective
Oxymorphone
Highly effective
Parameters highly
variable for baseline,
presurgery assessment,
and surgery
Ketoprofen
If behaviors
pain-related,
ketoprofen not
effective
Buprenorphine
Altered behavior
from baseline
Behavioral and
movement analysis
-active, inactive,
grooming, sleeping,
position, and
attentive
None
Rat
Acute, surgical
(laparotomy)
1999, Flecknell,
et al. (27)
-Food and water
consumption
Body weight
Food and water intake
and body weight useful
parameters
Buprenorphine
jello
Effective
Rat
Acute, surgical
(laparotomy)
1998, Liles,
et al. (28)
-Food and water
consumption
Behaviors
-sleeping
-sitting
-grooming
-licking
-exploring
-walking
-running
-eating
-drinking
Body weight
Food and water intake and
body weight useful
parameters, Behavioral
assessment: licking and
sleeping most useful, but
interpret with caution
Morphine
Effective
Buprenorphine
jello
Effective
-Locomotor activity
-Food and water
consumption
Body weight
Food and water intake and
body weight useful
parameters, locomotor
activity not influenced by
analgesic use
Buprenorphine
Effective
Carprofen
Effective
Flunixin
Effective
Rat
Acute, surgical
(laparotomy)
1994, Liles and
Flecknell (29)
(Naltrexone
evaluated to
confirm that
endorphins
not affecting
variables
measured in
this model)
Rat
Acute, surgical
(laparotomy)
1993, Liles and
Flecknell (17)
-Locomotor activity
-Food and water
consumption
Body weight
Food and water intake and
body weight useful
parameters, locomotor
activity not influenced by
analgesic use
Buprenorphine
Effective
Rat
Acute, surgical 1991, Flecknell
(unilateral
and Liles (30)
nephrectomy)
and jugular
venous catheter
-Locomotor activity
-Food and water
consumption
None
Food and water intake
useful parameters,
locomotor activity with
variability
Nalbuphine
Effective (six doses
more effective
than three doses)
Mice
Chronic
(advanced
tumors)
1997, Vanloo,
et al. (31)
-exploration
-grooming
-posture
-food and water
consumption
-fur quality
None
Concluded these
parameters suggest
discomfort but not
necessarily pain
Buprenorhine gel Insufficient
Amphibians
Acetic acid
test
2001, Stevens
et al. (21)
Motor response
None
-wiping off acid
Behavioral assessment
-corneal reflex
-righting reflex
-hind limb withdraw
(to evaluate level of
sedation)
Parameters useful to
evaluate analgesia versus
sedation or underlying
motor dysfunction
Many
Some more effective
than others
(see reference for
details)
Miniature
pigs
Acute, surgical
(coronary
stent)
2001, Wilkenson,
et al. (32)
-mentation
-behavior
-appetite
Subjective observation,
no correlation between
physiologic parameters
and drug levels
Transdermal
fentanyl patch
Slow onset, prolonged
elimination,
therapeutic levels
achieved
Swine
Superficial,
deep surgical,
organ
dysfunction,
inflammation,
dental,
ophthalmic,
other
2001, Rodriguez,
et al. (33)
(By chart review)
None
-lethargy
-anorexia
-vocalizing
-locomotor deficits
-teeth grinding
-abdominal splinting
Inconsistent nomenclature
and lack of standardization
Buprenorphine
Effective except not
always sufficient to
alleviate pain from
inflammation
Volume 42, No. 4 / July 2003
Vital signs,
vomiting,
defecation,
drug levels
CONTEMPORARY TOPICS © 2003 by the American Association for Laboratory Animal Science
15
Table 1. Summary of selected articles using pain scales in animals (cont.)
Species
Quality of pain
Year, study
Dog
Acute, surgical
(soft tissue or
orthopedic)
1994, Hellebrekers, Pain
et al. (34)
-biting/licking wound
-restlessness
-abnormal stance
-vocalization
Level of sedation
Acute, surgical
(orthopedic)
Dog
Cats
Cats
Sheep
Lambs
Acute, surgical
(ovariohysterectomy)
Acute, surgical
(unspecified)
Acute, surgical
(orthopedic)
Physiologic
criteria evaluated
Conclusion of
parameter usefulness
Analgesia
evaluated
Analgesia
evaluated beneficial?
Respiratory rate,
heart rate, body
temperature
No interpretation
of usefulness of
parameters
Buprenorphine
Effective
Nalbuphine
Effective
Analgesia
Respiratory rate,
1984, Taylor
and Houlton (35) -unsolicited howling ABG (arterial blood
-resents manipulation gas)
of surgical site
-comfortable but
slightly uneasy
-very comfortable
Level of sedation
Pain assessment may be
subjective or effects of
analgesia (interpret with
caution)Respiratory rate
and ABG to evaluate for
respiratory depression
from analgesics—
none seen
Morphine
Equivalent analgesic
effect without
undesirable side
effects
1998, Slingsby
and WatermanPearson (36)
Observer bias a risk,
difficult to distinguish
pain from analgesia
1996, Stanway ,
et al. (37)
2000, Otto et
al. (38)
Acute, surgical 1997, Molony
(castration and/ and Kent (24)
or tail dock,
varying
combinations
producing
variable
severity of pain)
Behavioral
criteria evaluated
Visual analogue
scale
-posture
-response to vocal
interaction, general
stroking, and wound
manipulation
None
Visual analogue
Heart rate,
scalerespiratory rate
Pain
-demeanor
-vocalization
-response to digital
stimulation of
wound
Sedation score
-attitude
-response to handling
Visual analogue scale
done by anesthetist, no
other interpretation
of parameters
Behavioral
Respiratory rate
-vocalization, activity,
food and water intake,
facial expression
Lameness
Adequate for evaluation
of postoperative analgesia
Behavioral
lying, posture
changes, locomotor
activity
Cortisol showed ceiling
effect, postural and
locomotor changes useful,
total lying time—no
difference for any group
Cortisol level
The CSU IACUC also requested pain scale development for some
protocols that would appear to benefit from the implementation of a pain-scoring system. The CSU IACUC suggested that
investigators performing studies which could result in pain develop pain scales and intervention criteria to provide for more
objective evaluation for pain recognition and alleviation. The
following parameters were generally considered in the development of species-specific pain scoring protocols:
• Evaluation of activity: overall activity usually decreases with
pain; however pacing, restlessness, and lameness may indicate pain
• Appearance: animals may be hunched, experience piloerection, may not groom, have discharge around the eyes and
nose (porphyrin staining), and/or be recumbent
• Temperament: increased aggression, guarding, or reluctance to interact
• Vocalizations: teeth-grinding, chattering, whining, or decreased vocalizations
• Changes in feeding behaviors: decreased food and water consumption; reduction in body weight, urine, or stool output
• Physiologic changes: heart rate, respiratory rate, blood pressure, body temperature, and skin color
• Evaluation of surgical sites: erythema, swelling, or discharge;
excessive licking or chewing of the surgical site.
Pain scores were devised by revisions of previously published
16
CONTEMPORARY TOPICS © 2003 by the American Association for Laboratory Animal Science
Buprenorphine
Pentazocine
Pethidine
Mildly effective
Buprenorphine
Ketoprofen
Variable, longer
duration
Most effective
Morphine
Effective
Buprenorphine
Effective, lower pain
scores, longer
duration
Buprenorphine
Effective
Piritramide
Effective
Lidocaine
Similar results as
control group and
tail dock alone
scoring systems (22, 23), modification of existing IACUC-approved pain scales, or developed de novo after consultation with
a veterinarian on the committee. Development of pain scales
was accomplished by first considering evaluative parameters
outlined in the preceding bulleted list, then customizing each
scale based upon the applicability to the particular study. For
example, a study involving orthopedic surgery scrutinized gait
and/or limb function closely, whereas a protocol investigating
an infectious agent that results in pneumonia would more closely
follow respiratory rate and systemic disease symptomatology
The CSU IACUC evaluates the appropriateness of the submitted pain scoring plan by using the following criteria:
1. Determination that all reasonably measured parameters
were considered;
2. Evaluation of the criteria used for assessing score variables;
3. Evaluation of the total score that would require institution
of further treatment;
4. Evaluation of the appropriateness of continued treatments
or euthanasia endpoints.
Pain score modifications often were requested by the IACUC
before full approval was granted to the protocol. In addition,
investigators often would modify scores after implementation if
different parameters could be identified that more accurately
reflected an animal’s condition than the initial pain scoring system would allow. For example, in one rabbit postoperative scoring
Volume 42, No. 4 / July 2003
Table 2. Pain scale for canine after orthopedic surgery
Criteria/Score
0
1
2
3
Agitation
Asleep or calm
Mild agitation
Moderate agitation
Hysterical
Crying
Not crying
Crying, responds to voice
or touch
Crying, does not respond to
voice or touch
N/A
Movement
None
Frequent position
changes
Thrashing
N/A
Heart rate: above
preoperative value
0%–15%
16%–29%
30%–45%
> 45%
Respiratory rate:
above preoperative value
0%–15%
16%–29%
30%–45%
> 45%
Gait at a walk
Weight-bearing continuously
Weight-bearing lightly
or intermittently
Toe-touches, not weight-bearing
Carries limb
Standing
Continuously weight-bearing
Intermittently weight-bearing
Carries limb
N/A
Joint effusion
None
Mild
Obvious
N/A
Stifle thickness (diameter
of operated stifle at the
level of the epicondyles)
Ratio of operated stifle to the
normal preoperative stifle,
score = ratio × 2
N/A
N/A
N/A
Total
N/A, not applicable.
Table 3. Pain scale for large animals after orthopedic surgery
Criteria/Score
0
1
2
3
4
Comfort (over-the-fence
observation)
Awake, interested in
surroundings,
recumbent, eating
Awake, not interested
in surrounding,
recumbent, reduced
appetite
Lethargic, depressed,
anorexic
Head down, lethargic
(drooped ears),
anorexic, bruxism
Recumbent, fixed gaze,
eyes half closed,
little response when
prodded, bruxism
Movement
Normal ambulation,
no lameness
Slight lameness,
toe-touching
Lameness, some
toe-touching, otherwise
limb carried
Lameness, limb carried
except when herded
Lameness, limb carries
when herded
Flock behavior
Normal, moves with
flock
Mild changes, lags
behind but catches up
Moderate changes,
lags behind but catches
up
Severe changes, no
interest in flock
N/A
Feeding behavior
Normal, at feed
trough
Mild changes
Moderate changes
Severe changes,
anorexic
N/A
Respiratory rate
(in shade)
Normal
Noticeable increase
Hyperventilation
Hyperventilation with
mouth breathing
N/A
Palpation soreness
and range of motion
soreness
None
Mild pain
Moderate pain
(withdraws limb)
Severe pain (withdraws N/A
limb, tries to bite or flee)
Soft tissue swelling,
joint effusion, heat
(centered around the
joint)
None
Slight
Mild
Moderate
Total
Severe
N/A, not applicable.
method, bruxism was added as a symptom of pain after it was noted
to be the primary manifestation of pain in some of the initial surgical cases; in a sheep spinal surgery, a pain score was replaced
with a neurological function scoring system that would more accurately record the animal’s condition. Because of dramatic
differences that occur between prey and predator species regarding pain expression (19, 24) and because of protocol-specific
clinical manifestations of pain or distress, in most cases investigators found it necessary to generate a new scoring protocol for a
procedure that was being performed for the first time.
Pain score record-keeping generally is performed by the principal investigator or his/her staff and is recorded on individual
animal records, surgery records, or a specially devised rodent
postoperative record that allows for observation of a larger number of animals on one record. The institutional veterinarian and
IACUC examine these records on a regular basis.
When protocols are resubmitted, or pain scores are adapted
to a new study, the committee often asks for a synopsis of scores
previously recorded in order to gauge the invasiveness of the
study and risk of non-alleviated pain. This data collection has
enhanced the IACUC’s ability to make objective decisions about
protocols that could potentially result in pain that would be otherwise difficult for committee members to predict. If the IACUC
felt a protocol could cause considerable pain, it requested a synVolume 42, No. 4 / July 2003
opsis of pain scores after a small pilot study. IACUC members
occasionally viewed animals postoperatively in order to visualize
the discomfort of the animal or to score the animals independent of the researcher to help reduce bias.
Although projects involving the same species undergoing similar procedures may use similar pain scales, in general it has been
desirable to customize pain scoring systems for each study. Examples of some pain-scoring systems that have been developed
and utilized by CSU investigators include those for sheep used in
orthopedic, neurologic, or reproductive research; horses in orthopedic or reproductive studies; guinea pigs used in mycobacterial
studies; rats used in orthopedic or neurologic studies; birds used
in orthopedic or analgesia studies; and rabbits used in orthopedic
studies. Tables 2 through 6 are the pain-scoring scales used. Pain
scores are totaled, and interventions are specific for each scale.
Each pain score is assigned a specific action plan. For example,
using the orthopedic pain score for rabbits, a score of > 4 would
necessitate supplemental analgesia and continued observation
(Fig. 1). Such a flow chart provides a logical action plan that the
IACUC can evaluate. It is often necessary to refine pain scoring
and intervention during the implementation of a protocol in
order to more accurately measure and alleviate pain.
Animal care technicians are often involved in performing the
pain assessments or administering the analgesics. To properly
CONTEMPORARY TOPICS © 2003 by the American Association for Laboratory Animal Science
17
Table 4. Pain scale for rabbits after femoral orthopedic surgery
Criteria/Score
0
1
2
3
Total
Standing
Continuous
weight-bearing
Intermittent
weight-bearing
Completely
non-weight-bearing
N/A
Gait with movement
Continuous
weight-bearing
Intermittent
weight-bearing
Toe-touches,
non-weight-bearing
Non-weight-bearing
Swelling
None
Mild
Obvious
N/A
Pain on palpation
of operated limb
None
Mild (occasional
vocalization)
Moderate (frequent
vocalization)
Severe (vociferous vocalization,
withdraws limb, bites, struggles)
Behavior
Normal cage exploration,
food and water
consumption, animal calm
in cage
Minimal exploration,
food and water
consumption
No cage exploration,
hunched posture, movement
when stimulated,
anorexic for 24 h
No cage exploration,
hunched posture, piloerection,
no movement, anorexic,
increased respiratory rate
or labored breathing
Body temperature
Normal
> 39.4°C and a lameness
score of 5; or > 40°C
and a lameness score
of < 5
> 40°C for 24 h post-treatment
(analgesia) and anorexic
> 40°C for 48 h post-treatment
(analgesia) and anorexic
Appearance of incision
Clean, no chewing,
no redness
Mild chewing, redness,
suture intact
Severe chewing, incision open
Incision infected (redness,
swelling, purulent drainage)
N/A, not applicable.
Table 5. Pain scale for rats in arthritis study
Criteria/Score
0
1
2
3
4
Total
Body weight
< 5% decrease
6%–10% decrease
11%–20% decrease
Lameness
None
Mild, single limb
lameness
Moderate, multiple limb Severe, non-weight
lameness
-bearing on any limb
N/A
Appearance
Normal
Huddled, mild
piloerection, moves
when stimulated
Huddled, moderate
piloerection,
reluctant to move
Huddled, ungroomed,
severe piloerection, no
movement, moribund
N/A
Arthritis score
Normal
Mild erythema, no
swelling or limb
deformity
Moderate erythema,
mild swelling, no
limb deformity
Moderate erythema,
moderate swelling,
mild limb deformity
Severe erythema,
severe swelling,
moderate to severe limb
deformity
Criteria/Score
0
1
2
3
4
Respiratory rate
(based on
preoperative levels)
< 10% increase
< 50 % increase
< 100 % increase
> 100% increase
N/A
Heart rate (based on
preoperative levels)
< 10% increase
< 50% increase
< 100 % increase
> 100% increase
N/A
Appearance
Cooing, standing on
Cooing, not standing
perch, feathers normal, on perch, or feathers
preening
ruffled
Quiet, not standing on
perch and feathers
ruffled
Huddled, not preening, N/A
unwilling to move
Body weight (compared
to prestudy values)
< 5% weight loss
< 15% weight loss
> 15 %, but < 20%
weight loss
21%–25% decrease
> 25% decrease
N/A, not applicable.
Table 6. Pain scale for birds after humeral orthopedic surgery
< 10% weight loss
Total
> 20% weight loss
N/A, not applicable.
score pain assessment of a species, it is important that personnel
are familiar with the normal behavior of the particular species.
The animal care technicians are often the ones most knowledgeable of the research studies and the species in their areas.
Therefore, they are the best candidates to perform this assessment and should be consulted and trained in pain-scoring
reporting. This practice allows for improved pain score validity,
inter-rater reliability, and internal consistency.
consequently, has improved communication between the committee and principle investigators. Most importantly, pain
scoring has resulted in improved methods for management of
pain and distress in laboratory animals.
Acknowledgments
We would like to thank all the CSU principle investigators, the animal
care technicians, and staff that have assisted and continue to assist in the
development of pain scales for laboratory animals.
Conclusion and Recommendations
Refinement of the species-specific pain scales is a continuing
process. Rigorous establishment of scale validity, inter-rater reliability, and internal consistency are needed. Nevertheless, the
pain scores described in this article have given researchers a
more objective and accurate form of pain assessment for animals undergoing procedures, allowing pain to be managed with
greater accuracy and consistency. Use of objective pain scoring
and interventional criteria has enabled both researchers and
the IACUC to more clearly delineate and predict outcomes and,
18
CONTEMPORARY TOPICS © 2003 by the American Association for Laboratory Animal Science
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