As described in the report, Recognition and Alleviation of Pain in Laboratory Animals (2009), there are some situations in which animal pain is unavoidable, such as when pain is a tool to motivate or shape behavior, or when pain is the focus of research. The ethical justification for such research should consider both the costs to the animal and the anticipated benefits of the research to humans and animals: the greater the cost to the research animals, the stronger the scientific and ethical justification of the research should be.
Laws and regulations require that investigators adequately control pain in research animals, unless the outcomes of an experiment would be negatively impacted. Alleviating pain in research animals typically refers to reducing its duration and/or intensity, as those two characteristics affect aversiveness.
Pain alleviation strategies may include preventative measures, therapeutic measures, or a combination of the two.
Preventative measures include appropriate animal handling and restraint, minimization of tissue trauma during surgery, the use of minimally invasive surgery techniques (such as fiberoptic technologies), and other non-pharmacological methods. The “Three Rs” (see below) provide the underlying principle to the ethical care and use of laboratory animals.
Therapeutic measures include the use of general and local anesthetics, sedatives or drugs that relieve anxiety, and analgesics.
- General anesthesia: Animals are anesthetized (completely numbed) in order to undertake procedures that would otherwise cause pain.
- Sedation/anxiety relief: These drugs are often used in combination or with general anesthetics to modulate, block, or relieve pain.
- Analgesia: These reduce pain locally or temporarily. Although analgesia is defined as “lack of pain,” complete elimination of pain in awake animals is commonly neither achievable nor desirable (the ability to feel some pain prevents an animal from further damaging an injured area, for example).
Pain management goals range from total elimination of pain as, for example, during general anesthesia for a surgical procedure, to pain that is tolerated without compromising the animal’s well-being. The full report provides reference tables to inform which approaches laboratory personnel should consider in circumstances of low, medium, and high levels of pain, as well as tables outlining the properties of various classes of drugs and when to use them.
The “Three Rs”
The “Three Rs” provide the underlying principle to the ethical care and use of laboratory animals:
- Refinement of experimental procedures to reduce or eliminate pain and distress. Where the use of animals is unavoidable, minimize pain, distress, lasting harm, or other threats to animal welfare. For example, researchers should ensure that accommodation meets animals’ needs; use pain treatment drugs; and specify humane endpoints—that is, when a study design should be changed or a study ended early due to concerns about animal pain, distress, or welfare.
- Reduction in the number of animals being used. Use methods that enable equivalent information to be obtained from fewer animals or more information from the same number of animals, such as through the use of advanced imaging techniques.
- Replacement of animals with other reliable models. For example, use alternative methodologies, such as computer modeling, or replace higher order animals with those of a lower order (such as using amphibians or invertebrates instead of mammals).