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Reducing Animals' Pain and Distress

In the Animal Welfare Act regulations, a painful procedure refers to "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" (9 C.F.R. § 1.1 (2022)). A principal investigator/researcher must consider alternatives to painful procedures to try to avoid or minimize the animals' pain and distress (9 C.F.R. § 2.31 (d)(1)(i-ii) (2022)). If painful procedures will be used, they must "be performed with appropriate sedatives, analgesics or anesthetics unless withholding such agents is justified for scientific reasons..." (9 C.F.R. § 2.31 (d)(1)(iv)(A) (2022)). To help meet these requirements, the Animal Welfare Information Center provides information regarding pain recognition, anesthesia and analgesia, humane endpoints, and euthanasia. 

Pain Recognition and Assessment Resources

The Animal Welfare Act requires pain and distress experienced by research animals to be minimized where possible (7 U.S.C. § 2143 (a)(3)(A)-(C) (2022)).  Therefore, it's critical for any personnel working with animals to recognize and assess animal pain and distress. This allows them to manage and minimize or eliminate the animals' pain and distress quicker. The resources below provide information on tools used to recognize and assess pain in various animal species. 

Grimace Scales

USDANAL. Animal Welfare Information Center.

Grimace scales are scoring systems used to assess pain in animals by evaluating different areas of the face and body posture. Grimace scales are currently available for a number of animals including laboratory animals, farm animals, pets, and wildlife. 

Recognition and Alleviation of Distress in Laboratory Animals

National Research Council (US) Committee on Recognition and Alleviation of Distress in Laboratory Animals.

This book aims to educate animal personnel on the scientific and ethical issues associated with pain and distress in laboratory animals. 

Anesthesia and Analgesia

Although the terms analgesia and anesthesia are often confused with one another, they have two different intentions when used. Analgesia is the relief of pain without the loss of consciousness or sensation using analgesics (e.g., Aspirin, Carprofen, etc.). Anesthesia is the loss of physical sensation with or without loss of consciousness using anesthetics (e.g., Ketamine, Propofol, Isoflurane, etc.). Both practices should be used in accordance with the Animal Welfare Act to ensure that pain and distress are minimized (7 U.S.C. § 2143 (a)(3)(A) (2022)). Treatment of pain should be tailored to the individual animal while taking the following factors into consideration: appropriate drug selection, dosage, procedure, degree of pain, patient health status, etc.

This section highlights some current analgesia and anesthesia best practices that can be referenced by individuals working with animals used for research, testing, education, and exhibition.

** The resources provided are for reference. Please consult with your institution’s veterinarian prior to using analgesics and anesthetics.


Additional Anesthesia and Analgesia Resources for Laboratory and Companion Animals

Guidelines on Anesthesia and Analgesia in Laboratory Swine

Unit for Laboratory Animal Medicine (ULAM). University of Michigan.

ULAM veterinary staff prepared these guidelines (reviewed in 2021) to provide recommendations for anesthesia and analgesia in laboratory pigs. 

Pain Management in Farm Animals: Focus on Cattle, Sheep and Pigs 

Molecular Diversity Preservation International (MDPI).

These 2021 recommendations focus on cattle, sheep, and pigs and provide an overview of pain management including assessment and treatment to improve animal welfare. 

Guidelines for Pain and Distress in Laboratory Animals (PDF | 239 KB)

National Institute of Health. Office of Animal Care and Use.

These guidelines (updated in 2020) discuss the ethical and legal responsibility of personnel involved with the use of animals in research to reduce or eliminate pain and distress in research animals. It also provides ways to both recognize pain and distress in research animals, as well as, intervene when pain and distress is observed in research animals. 

Laboratory Animal Anaesthesia (PDF | 4.55 MB)  

Comparative Biology Centre. Newcastle University.

The 3rd edition book (published in 2009) provides information on best practices in various aspects of laboratory animal anaesthesia. Some topics include techniques, equipment, and some basic guidelines for handling different species. 

Analgesic Best Practice for the Use of Animals in Research and Teaching - An Interpretive Literature Review)  (PDF | 112 KB)

National Animal Ethics Advisory Committee (NAEAC).

NAEAC gives an update to the previous ‘Analgesic Best Practice for the Use of Animals in Research and Teaching- An Interpretative Literature Review written in 2002.

Veterinary Anesthesia and Analgesia, 5th Edition

Lumb and Jones 5th Edition.

Veterinary anesthesia continues to evolve as a science and specialty within the veterinary profession. This book (published in 2015) discusses some of the most current best practices in anesthesia, analgesia, and pain management.

 American Animal Hospital Association Anesthesia and Monitoring Guidelines for Dogs and Cats

American Animal Hospital Association (AAHA).

AAHA's 2020 guidelines provide a framework for the safe delivery of anesthesia as a continuum to dogs and cats.

Additional Anesthesia and Analgesia Resources for Wildlife, Zoo, and Marine Animals

Anesthesia and Pain Management in Exotic Exotics (Zoo Animals)

VIN. World Small Animal Veterinary Association Congress Proceedings.

In this 2017 paper, VIN discusses approaches to anesthesia, sedation and analgesia in wild vs. domesticated animals regarding a swift approach of administration vs. a titration approach. 

Comparative Anesthesia and Analgesia of Aquatic Mammals (PDF | 828 KB)   

Veterinary Anesthesia and Analgesia: The Fifth Edition of Lumb and Jones.

These guidelines reflect internationally acceptable and scientifically valid approaches to handling and treatment of marine mammals in field research. 

Guidelines for Field-Based Surgery and Anesthesia of Free-Ranging Wildlife

Chinnadurai SK, Strahl-Heldreth D, Fiorello CV, Harms CA. Best-Practice Guidelines for Field-Based Surgery and Anesthesia of Free-Ranging Wildlife. I. Anesthesia and Analgesia. J Wildl Dis. 2016 Apr;52(2 Suppl):S14-27. doi: 10.7589/52.2S.S14. PMID: 26845296.

Field anesthesia is often needed for both invasive and noninvasive procedures on wild animals. In this 2016 paper, the authors describe basic principles of safe anesthetic delivery, monitoring and recovery in free-ranging wildlife. 

Humane Endpoints and Euthanasia

Humane endpoints are an important refinement that should be incorporated in animal experiments, especially if animals may experience pain and distress. A humane endpoint is the point at which an animal’s pain and/or distress is terminated, minimized, or reduced using methods such as euthanasia, terminating the painful procedure, relieving the pain with treatment, or restoring a basic requirement (e.g., returning an animal to social housing if isolation causes distress). Some examples of humane endpoints include a certain change in body temperature, body weight, or expression of specific behaviors. When selecting a humane endpoint, consider the various stages of discomfort, and the pain and distress the experiment may cause. An endpoint should be established before it is obvious that the animal will die unless the action is terminated, yet still be compatible with the experiment’s objectives. This promotes animal welfare while also gathering the necessary data from the experiment.


  • AVMA Guidelines for the Euthanasia of Animals

    American Veterinary Medical Association (AVMA).

    AVMA's 2020 guidelines give veterinarians guidance in relieving pain and suffering of animals that are to be euthanized. 

  • Guidelines for Endpoints in Animal Study Proposals [pdf, 7 pages]

    DHHSNIH. Office of Animal Care and Use.

    Selection of appropriate endpoints requires careful consideration of the study's scientific requirements, possible pain, distress or illness the research animals may experience, the most likely time course and progression of those adverse effects, and the earliest most predictive indicators of present or impending adverse effects.

  • Humane Endpoints in Laboratory Animal Experimentation

    3Rs-Centre Utrecht Life Sciences.

    Find information on why to use humane endpoints, types of humane endpoints, implementing them in research, and development and validation of humane endpoints. 

  • Humane Endpoints for Animals in Pain

    National Research Council (US) Committee on Recognition and Alleviation of Pain in Laboratory Animals.

    Chapter 5 of "Recognition and Alleviation of Pain in Laboratory Animals" discusses humane endpoints and their application in various research areas that involve animals experiencing pain during research. 

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