Debates about using animals in research rest on the special, sometimes contested interpretation of key terms. Several of them are provided here by participants in The Hastings Center’s project on biomedical research with animals. In the interest of fostering clear and civil discussion of the ethical controversies, The Hastings Center invites further discussion and development of the glossary. Fill out the form below and send it to us.

Alternative: This word is used in different ways. (1) Sometimes it refers to non-animal models (that is, an alternative to animals, but sometimes (2) it refers to another, less objectionable animal model (an alternative to the original animal), and sometimes (3) to any approach that reduces, refines, or replaces research methods using animals (an alternative to the original research method).
Animal: (1) In common parlance, an animal is any multicellular but nonhuman member of the kingdom Animalia. (2) In the Animal Welfare Act, however, an animal is “any live or dead dog, cat, nonhuman primate, guinea pig, hamster, rabbit, or any other warm blooded animal, which is being used or is intended for use for research, testing, experimentation, or exhibition purposes or as a pet. This term excludes: Birds, rats of the genus Rattus and mice of genus Mus bred for use in research.” Thus more than 95 percent of the (taxonomic) animals used in biomedical research are not defined as animals in the act. (3) In the Guide for the Care and Use of Laboratory Animals, which sets mandatory standards for all research facilities receiving federal funds, meanwhile, an animal is “any vertebrate.”
Distress: A typical definition is found in Merriam-Webster’s Collegiate Dictionary:“a pain or suffering affecting the body, a bodily part, or the mind.” The Animal Welfare Act requires research facilities “to ensure that animal pain and distress are minimized, including adequate veterinary care with the appropriate use of anesthetic, analgesic, tranquilizing drugs, or euthanasia.” The account is open to interpretation, and the relationship of pain and distress to cognition is a key issue.
Euthanasia: Animals used in experiments are often euthanized. In the context of animal welfare, euthanasia means killing animals as painlessly as possible. However, advocates for animal welfare argue that the means of euthanizing research animals sanctioned by the American Veterinary Medical Association cause pain and distress.
Humane: The Animal Welfare Act describes the humane treatment of laboratory animals this way: “minimum requirements with respect to handling, housing, feeding, watering, sanitation, ventilation, shelter from extremes of weather and temperatures, adequate veterinary care, including the appropriate use of anesthetic, analgesic or tranquilizing drugs . . . and separation by species.” This definition excludes enrichment and other efforts to meet species-specific needs, such as companionship.
Necessary: In the context of biomedical research, “necessary” refers to what is needed to carry out an experiment and what is needed for the humane handling, care, or treatment of laboratory animals. The word sometimes also refers to whether an experiment is itself needed to attain some medical or scientific goal.
Not Tested on Animals: This phrase, found on some product labels, does not necessarily mean that the product involved no animal testing. It can mean that (1) the final product was not tested on animals, although ingredients were; (2) the manufacturer or distributor did not test the product on animals, although someone else did; (3) the animal tests were done more than five years ago; or (4) the final product and its ingredients really were not tested on animals.
Pain: According to the International Association for the Study of Pain, pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Pain control in laboratory animals is challenging and controversial – whereas acute pain is relieved with short-term use of analgesics, the answer to chronic pain tends to be euthanasia.
Reduction: One of the “three Rs” (along with refinement and replacement) often taken to guide the use of animals in biomedical research, reduction refers to efforts to use fewer animals to perform an experiment or test. Reduction can be achieved, for example, by using research methods that allow comparable amounts of data to be obtained with fewer animals or that allow more data to be obtained with a given number of animals.
Refinement: This term refers to the use of techniques and procedures that minimize pain and distress in research animals.
Replacement: The primary meaning is the use of research methods that do not involve sentient animals. Examples include computer modeling and research on tissue culture, microorganisms in culture, or human volunteers. Replacement also sometimes refers to research conducted on tissue taken from an animal instead of on the whole animal.
Welfare: Animal welfare is concerned with assuring humane treatment of animals: maintaining good health, minimizing negative states such as pain, enhancing positive states, and giving animals the freedom to behave in ways that are natural to the species. What constitutes humane treatment is open to interpretation.

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