Minimizing Pain and Distress

Background & Definition

A painful procedure is defined as “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 is applied, that is, pain in excess of that caused by injections or other minor procedures.”1 

Distress and discomfort are harder to define.  Stress is defined as the body’s reaction to a change that requires a physical, mental or emotional adjustment or response.  Many factors can induce distress in laboratory animals, including fear, anxiety and environmental variables. 


Procedures and disease models that produce more than momentary pain, distress and discomfort are an unavoidable part of research with animals; such procedures require the appropriate use of sedatives, anesthetics, or analgesics, unless withholding of such agents is scientifically justified in writing and approved by the IACUC.  All potentially painful or distressful procedures must be identified in the Animal Care and Use Protocol; the protocol must include criteria that will be used to assess pain and distress in the animals and describe the actions that will be taken to minimize it, such as the use of anesthesia and analgesic agents and identification of alternative humane endpoints.  Consultation with ULAR veterinarians is strongly recommended.


Procedures considered to produce minimal, transient, or no pain and distress when performed by competent individuals using recognized methods:
  • Administration of experimental or therapeutic agents via intravenous, subcutaneous or intraperitoneal routes;
  • Venous blood collection;
  • Gastric lavage;
  • Stimuli that produce only transient pain and/or are escapable or avoidable (e.g., mild foot shock);
  • Common species-specific activities such as wheel running in rodents.
Procedures considered to produce pain or distress, and the use of anesthesia or analgesics to alleviate pain and or distress is required, unless a detailed written justification is submitted and approved by the IACUC:
  • All surgical procedures, regardless of whether a body cavity is opened or penetrated and regardless of whether the animal is allowed to recover;
  • Recovery from surgical procedures;
  • Wounding or induction of injury/disease states such as burns or radiation exposure;
  • Injection or application of compounds with induce excessive inflammation or necrosis (e.g., bradykinin, Complete Freund’s Adjuvant; infectious agents, etc.)
Some procedures are not directly associated with pain, but may cause distress in the animal; palliative procedures should be performed whenever possible to reduce pain, distress and discomfort to the lowest level possible: 
  • Food and/or water restriction beyond that required for normal presurgical preparation.
  • Stress paradigms such as forced swimming, inescapable noise or other stimulation
  • Inescapable noxious shock or thermal stress.
  • Paralysis or immobility in a conscious animal
  • Infectious and inflammatory disease models

Animals exhibiting signs of pain, discomfort or distress such as  (but not limited to) weight loss, decreased appetite, abnormal activity level, adverse reactions to touching inoculated areas, open sores/necrotic skin lesions, abscesses, lameness, conjunctivitis, corneal edema and photophobia must receive appropriate relief unless written scientific justification has been reviewed and approved by the IACUC.


1 USDA Animal Welfare Policy #11, 3/25/11

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