Guidelines for pain and distress in laboratory animals:
Guidelines for Pain and Distress in Laboratory Animals: Responsibilities, Recognition and Al eviation Introduction
Animals can experience pain and distress. It is the ethical and legal obligation of all personnel
involved with the use of animals in research to reduce or eliminate pain and distress in research animals
whenever such actions do not interfere with the research objectives. The Institutional Animal Care and
Use Committee (IACUC) has the delegated responsibility and accountability for ensuring that al animals
under their oversight are used humanely and in accordance with a number of Federal Regulations and
policies.2,21,29,30,32 Key to fulfilling the responsibilities for both the principal investigator (PI) and the
• understanding the legal requirements,
• being able to distinguish pain and distress in animals from their normal state, and
• to relieve or minimize the pain and distress appropriately;
The IACUC must assure that all aspects of the animal study proposal (ASP) that may cause more than
transient pain and/or distress are addressed; alternatives6 to painful or distressful procedures are
considered; and that methods, anesthetics and analgesics to minimize or eliminate pain and distress are
included when these methods do not interfere with the research objectives; and that humane end
points have been established for al situations where more than transient pain and distress can not be
avoided or eliminated. Whenever possible, death or severe pain and distress should be avoided as end
points. A written scientific justification is required to be included in the ASP for any more than transient
painful or distressful procedure that cannot be relieved or minimized.
The obligation to reduce pain and distress does not end with the review of the ASP. It is the
responsibility of the animal care staff, the research staff, veterinarians and the IACUC, to continue to
monitor animals for pain, distress, il ness, morbidity or mortality during the course of the research study.
If unexpected pain or distress occurs, and is more than an isolated incident, the PI must submit an
amendment delineating the unexpected problem and stating their proposed resolution to the issue (e.g.
administration of analgesics, lowering the dose of a drug that was administered, etc.). Alternatively, the
PI could justify the need for unrelieved pain or distress in the amendment, or in the case of regulated
If it is necessary to make changes in the ASP procedures, the PI must submit an amendment to the
IACUC and receive approval prior to instituting the modification. For example, if unexpected pain or
distress was noted following treatment with a specific dose of an experimental agent, the PI must
submit an amendment delineating the unexpected problem and stating their proposed resolution to the
issue (e.g. administration of analgesics, lowering the dose administered, etc.). Alternatively, the PI could
justify the need for unrelieved pain or distress in the amendment, or in the case of regulated species as
Recognition of Pain and Distress
Animals must be monitored by trained individuals for pain and distress as appropriate for the
species, condition and procedure. Critical to the assessment of the presence or absence of pain or
distress is having the ability to distinguish between normal and abnormal animal behavior. This is
especially true when dealing with species that often exhibit pain and distress with only subtle changes in
their behavior22 (see Table 1). Therefore, it is critical that the individuals assessing an animal be trained
in the species specific signs of pain and distress, as well as be knowledgeable of the potential outcomes
of the procedure, surgery or treatments administered to the animal. Pain and distress scoring is a
method to convert subjective animal observations in to objective scoring system which some have
found to be helpful in assessing animal behavior.
Whenever more than transient pain or distress is anticipated preemptive measures should be taken
to minimize or prevent the development of pain and/or distress. Following the implementation of
preemptive or palliative measures, animals must be monitored1,26 to ensure the efficacy of the measures
taken and determine if or when additional treatment wil be necessary. The extent and frequency of
monitoring will depend on the level of post-surgical/procedural pain and/or distress anticipated and the
chosen intervention strategy(s). For example, animals undergoing a procedure known to produce no
more than minimal/transient pain or distress may be adequately monitored by the daily observation of a
trained animal caretaker. Whereas, the monitoring of an animal undergoing a procedure known to
result in severe pain and/or distress may require more frequent monitoring by a team of trained
individuals (e.g. trained animal care staff, technicians, veterinarians, investigators, etc.). Animals
undergoing pilot studies or procedures new to the investigator or facility may also require a higher
frequency of monitoring and a team approach.
It is ultimately the responsibility of the PI and the personnel conducting the procedure to ensure the
timely and adequate identification, monitoring and documentation of the animals undergoing
potential y painful or distressful procedures. Investigators may request the assistance of institute and
facility veterinary and technical personnel when monitoring their animals, but al individual(s)
responsible for monitoring an animal must be identified prior to conducting the procedure and their
accountability clearly delineated and accepted.
Animals should be observed a minimum of once daily or more often based on professional judgment
and the research being conducted. The animals should be monitored for expected and unexpected signs
of more than transient pain or distress and, if observed, appropriate intervention strategies
implemented (e.g. non-pharmacological approaches, analgesics, anesthetics, euthanasia, etc.), unless
the withholding of treatment is scientific justified. Observations and actions taken to relieve pain or
The documentation of monitoring of the animal is important and required. The nature and the
frequency of the documentation are dependent on the species and the potential for pain and/or
distress. For example, the identification of cages containing an animal which has under gone a
potentially painful or distressful procedure with a “special observation” cage card has proven helpful in
drawing special attention to the animal during the caretaker’s daily health check. Cages containing
animals requiring more intensive monitoring should also be appropriately identified and their
monitoring and/or treatments documented either at the room, cage or animal level (e.g. room log, cage
card, medical record, etc.), in addition to the investigator’s notations in their laboratory notebook.
Documentation must be available to al personnel monitoring the cage or animal (i.e. IACUC,
veterinarians, animal care staff, etc.).
Strategies for the management of pain and distress may include non pharmacological considerations
(e.g. modified housing and husbandry practices, dietary modifications, surgical approaches8,
desensitization and acclimation strategies, etc.), pharmacological interventions or euthanasia. The
chosen strategy wil vary with the species, the procedure(s) being performed, duration of action needed,
route of administration preferred, degree and type of analgesia required and research being conducted
(see Table 2). It is strongly suggested that PIs consult their IC veterinarian during the development of an
animal study protocol, prior to its submission to the IACUC. This approach has been demonstrated to
Excellent resources3,4 and formularies7,10,12,14,15 are now available which provide extensive
information on the recognition and al eviation of pain and distress in laboratory animals (See Plumb
Veterinary Drug Handbook26 and other references below). These resources, coupled with trained and
skilled animal care personnel and the professional judgment of your IC and animal facility veterinarian
provides each investigator and their IACUC with powerful tools for the recognition and alleviation of
pain and distress in laboratory animals.
Preemptive measures should be taken to minimize or prevent the development of pain and/or
distress. For example, a skilled surgeon can often minimize tissue trauma which in turn minimizes post-
operative pain and distress. The use of ketamine or opioids preemptively, even in low doses has been
demonstrated to prevent the development of some forms of pain.24 In addition, the use of a single dose
of a non-steroidal anti-inflammatory agent (NSAID), sustained-release formulations,13 or other analgesic
agent can have a positive effect on the speed with which animals return to normal behavior.16,17,36,37,38 It
has been repeatedly demonstrated in humans that the provision of effective analgesia reduces the time
There are also many pharmacological intervention strategies for the management of pain and
distress. Traditional analgesics include local or regional anesthetics, opioids and NSAIDS. Using two or
more of classes of these analgesics together, or combining these analgesics with nontraditional
analgesics such as NMDA antagonists,20,40 alpha2-agonists,35 tramadol,5 and even the antiepileptic drug
gabapentin27 has been shown in both human and veterinary patients to enhance analgesia and allow a
reduction in the use of more powerful analgesics. This approach, cal ed multimodal analgesia also has
the advantage of providing even analgesic dosing thus promoting the animal’s well being.
For procedures in which the pain intensity is anticipated to be high, techniques such as constant rate
infusions of local anesthetics and or opioids either systemically, locally at the surgical site or via an
epidural catheter and transdermal preparations of drugs provide uninterrupted analgesia and are being
used successfully in larger laboratory animals.9 The analgesic regimen chosen should always be made in
The relief of pain and distress in research animals is ethical y sound, humane, and promotes good
science. The establishment of clear lines of responsibility coupled with appropriate endpoints,
monitoring and intervention strategies are key to the prevention, minimization and/or al eviation of
pain and distress in laboratory animals. Several excellent references and formularies are available to the
researcher, veterinarian and husbandry personnel to facilitate their ability to recognize and modulate
pain and distress in laboratory animals. Experience has demonstrated that a dynamic, interactive team
approach to the recognition and alleviation of pain and distress in laboratory animals yields results that
protect animal-welfare while promoting good science.
Revised - 07/14/04; 05/16/07; 07/14/10; 11/14/12
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Regulations (CFR), Title 9, Chapter 1, Subchapter A, Parts 1, 2, and 3.
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TABLE 1: POTENTIAL SIGNS ASSOCIATED WITH PAIN OR DISTRESS IN RATS, MICE AND RABBITS Mice Rats Rabbits
Unkempt Appearance (Erected, Matted, or Dul Haircoat)
Abnormal Posture/Positioning (e.g., Head-pressing, Hunched Back)
Tearing (including Porphyria), Lack of Blinking Reflex
Redness or Swelling Around Surgical Site
TABLE 2: POST PROCEDURAL PAIN POTENTIAL a,b Minimal to Mild c Mild to Moderate d Moderate to Severe e
Subcutaneous transponder placement C-section
a Table adapted from “Guidelines for the Assessment and Management of Pain in Rodents and Rabbits”. 2006,
American College of Laboratory Animal Medicine
b The analgesia and monitoring required may vary due to a number of factors; such as the invasiveness of the
procedure, degree of tissue trauma, surgical time, skil of the surgeon, and the tissues or organs involved.
c Post procedural pain relief for minimal to mild pain may be adequately addressed with preemptive analgesia,
tissue infiltration with a long acting local anesthetic, and a single dose of a long acting NSAID or mixed opioid
d Post procedural pain relief for mild to moderate pain may be adequately addressed with tissue infiltration with a
long acting local anesthetic combined with one or more doses of a long acting NSAID and/or an opioid or other
agent in addition to pre-emptive analgesic administration.
e Post procedural pain relief for moderate to severe pain should encompass multimodal analgesia (e.g. combining a
pure opioid agonist with a NSAID, tissue infiltration with a long acting local anesthetic, etc.)
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