that stress is a departure from physiological and behavioral homeostasis with the “stress 
response” resulting in behavioral and physiological adaptations designed to return the 
organism to homeostasis. This definition includes stressors that are not harmful and may be 
beneficial — for instance, gravitational stress is necessary for maintenance of bone density. 
The prevalent thinking is that stress becomes harmful when it is sufficiently prolonged or is of 
such a magnitude that adaptation is not successful or not possible. Thus, a distinction is 
often made between the inability to adapt and a stressor. Understanding this distinction from 
a scientific perspective is the topic of intensive ongoing research. 
ROLE OF ADAPTATION, HABITUATION, AND CONDITIONING 
The state of adaptation, habituation, or conditioning for any organism is an important 
consideration in determining the acceptability of any proposed treatment or experimental 
condition. The aversiveness and harm of procedures such as restraint, drugs, and other 
stressors are highly dependent on the history and experience of the animal. For example, cold 
conditions that may be entirely normal or even important for wild animals may be 
unacceptable for unconditioned laboratory animals. This also means that all individuals 
responsible for the care and use of animals must be appropriately trained on the natural 
biology and proper laboratory handling of the species under study. 
IMPORTANCE OF SPECIES ANDETHOLOGICAL CONSIDERATIONS 
Animal welfare rules have been designed around the species and preparations most common 
in laboratory practice. It is up to the LACUC to judge the appropriateness of such rules for the 
species and experimental conditions in a given protocol; deviations to the regulations must be 
scientifically justified, and animal welfare must be optimized given the experimental 
conditions. Nevertheless, some exemptions require waivers from the USDA. The IACUC has 
been given wide latitude to provide exceptions to the rules where it is required by needs of a 
particular species. Thus, some species may be harmed by a continuous flow of fresh air in 
ethological laboratory settings or by the stainless steel environment of the typical animal care 
facility. Under such circumstances, with an appropriately written rationale, the IACUC should 
consider a deviation from standard laboratory animal practice. 
CHANGE IN ETHICS, VALUES, AND KNOWLEDGE 
The principal investigator, the IACUC, and the animal care staff must be aware that they are 
working in an environment in which there are ongoing changes in scientific knowledge and 
public values, which in turn will require regular re-evaluation of protocols. Strong, ongoing 
communication between the IACUC, the veterinarian, the animal care staff, and the 
investigator is essential to managing these changes smoothly. 
PROVIDE OCCUPATIONAL HEALTH SERVICES 
Two NRC Reports including Occupational Health and Safety in the Care and Use of Research 
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