TEAM APPROACH TO SETTING LIMITS 
Laboratory animals, like humans, vary in their response to experimental conditions. When 
experimental conditions have potential consequences that may result in morbidity or 
mortality, the investigator, veterinarian (including animal care staff), and IACUC should work 
together to determine the appropriate limits beyond which the animal is removed or relieved of 
the condition(s) causing the morbidity. While the IACUC is responsible for approving protocols 
and the attending veterinarian can terminate experiments under certain conditions, the 
behavioral investigator is often in the best position to understand the risks for a particular 
animal in any experimental design and to detect animal pain or suffering in the course of an 
experiment. To the extent possible, it is valuable for the investigator to anticipate and define 
limits and endpoints in protocol preparation and review stage. It is in the interest of the 
animals and the institution for the IACUC, the veterinarian, the animal care staff, and the 
investigator to work together as a team to foster good animal care and good science. 
LEVEL EVALUATION OF THE EXPERIMENTAL VARIABLE 
It is difficult to make general conclusions from a study that uses only one level of an 
experimental variable (e.g., drug dose, stimulus intensity, or reinforcement magnitude). The 
results of an experiment are influenced by many variables. In an effort to maintain the 
consistency of their data, researchers may reduce the number of variables in their experiment. 
However, it is wise to keep in mind that results may not be similar if obtained under a 
different combination of variables. For this reason, "recommended" values for an 
experimental variable (e.g., the number of hours of fluid restriction, the number of amperes of 
electric shock) are not provided in this document. Experience has taught that the critical 
value of certain parameters may change substantially depending upon other variables (e.g., 
the animal's species, age, sex, and history of exposure to the experimental variable). 
SPECIES OF ANIMALS 
This document addresses methods proven for use with rodents, the species used in much of 
the research and teaching in the United States. Considerable attention also is devoted to 
methods with nonhuman primates to gain insight into welfare issues, because they are 
important models in behavioral studies. Behavioral research methods similar to those 
reviewed here have also been used to study large farm animals (e.g., Arave et al., 1992). 
Investigators using farm species should consult the National Research Council (NRC) Reports 
for those species (ILAR, 1996; Federation of Animal Science Societies, 1999). Chapter 9 of this 
report, Ethological Approaches, reviews procedures for studies of behavior in the wild, which 
often involves species not traditionally used in the laboratory. 
STRESS VERSUS DISTRESS 
For scientific investigations, stress is an elusive concept, with almost as many different 
definitions as there are investigators. At the core of most definitions, however, is the notion 
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