Standard on Assignment of Animals Into Pain Categories


University of North Carolina at Chapel Hill Standard on Assignment of Animals Into Pain Categories



The University of North Carolina at Chapel Hill is required to report an annual census of the number of animals used in research and teaching, the type of species used, and the number of animals placed in each of the four “Pain Categories (B, C, D and E)”. In order to meet these requirements, it is essential that pain category information be provided by investigators prior to initiating any animal-related research or teaching activities. The intent of this document is to provide general recommendations and guidance on how to assign animals to the different pain categories.

Scope of Applicability

All personnel involved with animal research at UNC-CH.

The UNC-CH Institutional Animal Care and Use Committee (IACUC) expects that anyone involved in animal work at the University will comply with this Standard. Requests for exceptions to this Standard must be reviewed and approved by the IACUC.


When completing the protocol, assign each animal listed on a protocol to one of the following categories: B, C, D or E. Be sure to list each animal under the highest pain category that will apply to the animal at any time while on the protocol. Do not include non-research related veterinary care in determining the pain category. Note that the severity or duration of the pain/distress or the use of anesthesia/analgesia to alleviate pain/distress could result in animals being placed in different pain categories.

Pain Categories (B, C, D and E) with possible examples (not comprehensive)

Category B: Animals being bred or held, but not used for research or teaching.

  • Breeding with no genotyping or euthanasia
  • Housing only
  • Observation in natural habitat having no physical contact with the animals

Category C Procedures involving either no pain/distress, momentary pain/distress or slight pain/distress. The level of pain/distress appropriate for this category would not typically require the use of anesthetics or analgesics.

  • Routine injections of non‐toxic, non‐irritating substances
  • Blood collection, such as tail nick, tail snip, and venous blood sampling
  • Tattooing, ear punching, ear notching, tail clip for genotyping and ear tagging
  • Tissue collection after approved AVMA euthanasia, without surgery (e.g. genotyping)
  • Restraint for non‐invasive procedures
  • Genetically engineered phenotype with unknown clinical health complications, but not expected to cause congenital pain/distress
  • Mild symptoms after inoculation, tumor induction, or infection by a viral/bacterial agent that do not require clinical treatment for pain relief or alleviation of symptoms
  • Observation of animal behavior in research setting, such as locomotion and social interactions
  • Assessment of responsiveness to mild noxious stimuli (e.g., hotplate, Von Frey) in which the animal can escape the stimulus
  • Mild, transient colitis
  • Mild to moderate ascites formation without systemic effects
  • Infrequent electric shocks from which an animal can escape or can avoid
  • Cancer studies limited to subcutaneous tumors that adhere to Policy

Category D Procedures which involve pain/distress or have the potential for pain/ distress and for which appropriate anesthetic, analgesic, or tranquilizing drugs are used. Below is a non-exhaustive list of conditions and procedures that may cause more than momentary or slight pain or distress: in each case, the pain/distress is alleviated by the appropriate use of analgesics or anesthetics.

  • All non‐survival surgeries
  • All survival surgeries
  • Exsanguination or transcardial perfusion under anesthesia
  • Any post procedural outcome resulting in evident pain, discomfort or distress that is treated with anesthetics or analgesics
  • Induced infections or antibody production with appropriate anesthesia or analgesia
  • Footpad injections under anesthesia
  • Injection or blood collection by invasive routes such as intracardiac, central vessel, or periorbital sites under anesthesia
  • Physical trauma under anesthesia
  • Single injection of Complete Freunds Adjuvant (Incomplete FA subsequent injections)

Category E Procedures that involve pain/distress or potential pain/distress not relieved with anesthetics, analgesics, or other methods for relieving pain/distress. The use of Pain Category E must be scientifically justified. Below is a non-exhaustive list of conditions and procedures that may cause more than momentary or slight pain/distress.

  • Persistent, severe colitis
  • Inflammatory conditions and microbial infections with significant systemic effects
  • Application of noxious stimulation, trauma or electric shock from which an animal cannot escape or which an animal cannot avoid
  • Genetically engineered phenotype that causes pain/distress that will not be alleviated
  • Procedures for which needed analgesics, tranquilizers, sedatives, or anesthetics must be withheld for scientific reasons
  • Exposure to abnormal or extreme environmental conditions
  • Arthritis models causing prolonged pain or discomfort
  • Prolonged restraint
  • Forced swim test or other measures of depression
  • Models of neurological or muscular impairment


Requests for exceptions to this Standard must be reviewed and approved by the IACUC and/or Division of Comparative Medicine (DCM) Veterinarians.


IACUC: Institutional Animal Care and Use Committee

DCM: Division of Comparative Medicine

University Standard: The minimum acceptable limits or rules used to achieve Policy implementation, enforceable by the IACUC.

Painful procedure: “...any procedure that would reasonably be expected to cause more than slight or momentary pain or distress in a human being to which that procedure was applied, that is, pain in excess of that caused by injections or other minor procedures.”

Related Requirements

External Regulations and Consequences Federal Animal Welfare Regulations (CFR Ch.1, 2.36(b) (5-7)

University Policies, Standards, and Procedures

For more detailed guidance, please refer to the University Policy on the Care and Use of Vertebrate Animals for Research, Training and Teaching Purposes.

Contact Information

Contact Information Table
Subject Contact Telephone Email

Standard Information

Office of Animal Care and Use


Standard Information

DCM Veterinarians



Important Dates

  • Effective Date and title of Approver: July 2018; UNC IACUC
  • Revision and Review Dates, Change notes, title of Reviewer or Approver:

Approved by: UNC IACUC

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Article ID: 132193
Thu 4/8/21 9:25 PM
Fri 5/19/23 1:40 PM
Effective Date
If the date on which this document became/becomes enforceable differs from the Origination or Last Revision, this attribute reflects the date on which it is/was enforcable.
10/21/2020 12:00 AM
Issuing Officer
Name of the document Issuing Officer. This is the individual whose organizational authority covers the policy scope and who is primarily responsible for the policy.
Issuing Officer Title
Title of the person who is primarily responsible for issuing this policy.
Vice Chancellor
Last Review
Date on which the most recent document review was completed.
04/19/2023 12:00 AM
Last Revised
Date on which the most recent changes to this document were approved.
04/20/2022 12:00 AM
Next Review
Date on which the next document review is due.
04/19/2024 12:00 AM
Date on which the original version of this document was first made official.
09/10/2019 12:00 AM
Responsible Unit
School, Department, or other organizational unit issuing this document.
Research-Institutional Animal Care & Use Committee