Alleviating Pain and Distress in Laboratory Animals

The American Association for Laboratory Animal Science (AALAS) endorses the United States Government Principles for the Utilization and Care of Vertebrate Animals Used in Testing, Research, and Training, which call for the avoidance or minimization of discomfort, distress and pain during these procedures. AALAS recognizes that the use of animals in research and teaching often creates a highly emotional debate with contradictory opinions within the public at large. Given that the advancement of scientific knowledge, particularly in the biomedical field, has been made possible by animal-based research(1), AALAS supports live animal research when it is performed in an ethical and humane manner. That is, anyone working with laboratory animals has the moral obligation to explore, consider, and implement any means for avoidance and minimization of pain and distress in laboratory animals, whenever possible.

Ensuring that the care and use of animals for research is conducted in a humane and ethical manner is a fundamental function of the Institutional Animal Care and Use Committees (IACUC). The Animal Welfare Act mandates that IACUCs oversee the care and use of animals covered by the Act(2). The Public Health Service (PHS) Policy on Humane Care and Use of Laboratory Animals(3) adopts a similar position. IACUCs are composed of scientists, veterinarians, a non-scientist, and at least one member not affiliated with the particular institution, often called a “community member.” The IACUC must review and approve any research protocol that proposes to use live, vertebrate animals in research, teaching, and testing. During the review, the committee must determine if (1) the proposed animal use is essential for achieving relevant scientific goals, (2) an appropriate species has been selected, (3) the number of animals requested is properly justified, (4) the care of the animals is appropriate, (5) the provisions for alleviating pain and distress are appropriate, and (6) alternatives to procedures that might cause pain or distress have been considered.

Institutions may use additional measures to ensure the responsible use of animals for research in their facilities by voluntarily participating in the assessment process for accreditation by the Association for Accreditation and Assessment of Laboratory Animal Care (AAALAC). AAALAC provides effective and comprehensive guidance, assessment, and monitoring to assure the highest standards of humane animal care and use.

Defining Pain and Distress
Pain is an unpleasant sensation that is highly subjective. The most widely accepted definition of pain is from The International Association for the Study of Pain, as follows: “An unpleasant sensory and emotional experience arising from actual or potential tissue damage or described in terms of such damage.”

Distress is more difficult to define, so its meaning is often described in the context of stress. In medicine, stress is a physical or psychological stimulus that can produce mental or physiological reactions. If these stimuli are strong enough and/or sustained over a period of time, stress leads to distress, the interruption of normal physiological functions, and, eventually, to illness. Distress has the potential to threaten an animal’s welfare(4).

AALAS Positions on Pain and Distress

  1. The ability of vertebrate animals to feel or perceive pain is not fully understood and the assessment of pain in non-verbal individuals is often difficult. Therefore, any event, procedure, or situation known to cause pain or distress in humans must be expected to cause pain or distress in nonhuman vertebrate animal species, as well, unless proven otherwise.
  2. The avoidance and minimization of pain and distress in laboratory animals is an ethical obligation that preserves the welfare of animals used in research, teaching, and testing, and optimizes the interpretation of scientific data collected during experiments.
  3. Any experimental, husbandry, or other procedure that has the potential to produce more than slight or momentary pain or distress (e.g., in excess of an injection of an innocuous substance) requires the consideration and implementation of pain-relieving measures, including but not limited to, the use of anesthetic and analgesic drugs, supportive care associated with surgical/painful procedures, social housing, acclimatization to stressful procedures, environmental modifications, and training to perform particular tasks allowing the animal some control over the situation. Preemptive measures should also be considered.
  4. If the research study requires the withholding of pain and distress relieving drugs, the researcher must provide compelling scientific justification and demonstrate to the IACUC that all other considerations have been taken into account to enhance the well-being of the animals, in order to secure approval prior to initiation of the study.
  5. The institution, through its IACUC, must ensure that all personnel involved in the care and use of animals are adequately trained. This includes proficiency in the following areas of expertise: procedures used for animal handling, experimental manipulations, and surgery; knowledge of the concepts and methods used to recognize pain and distress in laboratory animals; and, knowledge of how to immediately alleviate pain and distress, either directly or by soliciting the assistance of trained professionals. Proper training raises awareness and provides personnel with the assurance that they are treating laboratory animals in a humane and ethical manner, so they can take pride in their vital work.
  6. Signs of pain and distress vary among species, and are sometimes difficult to discern. Therefore, trained veterinary professionals should be involved in the design, monitoring, and documentation of experiments that have the potential to cause more than momentary pain and distress to laboratory animals.
  7. Researchers must describe humane end-points in protocols where pain and distress are expected. The humane end-points selected should be appropriate for the species and the experimental procedures. Studies inducing pain and distress must be monitored by research staff, as well as by trained veterinary professionals, to ensure that protocol-specified treatments or other interventions are administered, and to assess whether humane end-points have been reached.


  1. Handbook of Laboratory Animal Science: Essential Principles and Practices v. 1 by Jann Hau (Editor), Jr. Gerald L. Van Hoosier (Editor) CRC Press. 2 edition; (28 Oct 2002) 
  2. The Animal Welfare Act and Animal Welfare Regulations 
  3. The U.S. Department of Health & Human Services Public Health Service Policy on Humane Care and Use of Laboratory Animals 
  4. Recognition and Alleviation of Distress in Laboratory Animals. Committee on Recognition and Alleviation of Distress in Laboratory Animals, National Research Council (2008).