heart rate, blood pressure, glucose levels). Many authors have pointed to the desirability of using multiple measures to obtain a more comprehensive data set (Rushen 1991). It is important to underscore that reliance on a single measurement of stress may result in erroneous conclusions. Chapter 3 provides more details on distress recognition.
There is a rich literature documenting the interference of stress in behavioral and/or physiological endpoints. Strong evidence in rodents has shown that mild stress of 2-3 months duration—a regimen that produces no signs of overt distress—alters the animals’ performance in tests of anxiety, depression, and memory (D’Aquila et al. 1994; Rossler et al. 2000; Song et al. 2006; Willner 1997). Other findings indicate that rats’ habituation to a test environment can dramatically affect their response to a toxic substance (Damon et al. 1986). On the other hand, in some cases (such as lower anxiety behavior in the elevated plus maze) the effects of stress may actually be beneficial to the experimental procedure, indicating that prolonged stress may not be uniformly detrimental. Chapter 3 documents the contamination of experimental data by unwanted or uncontrolled stress due to inadequate husbandry, noisy environments, olfactory stimuli, or other factors.
The impact of distress on both animal welfare and research results is likely even more pronounced than that of stress. Animals exposed to prolonged severe stress experience underlying changes in physiological functions (e.g., gastric lesions [Ushijima 1985] or immunosuppression [Tournier 2001]) that can interfere with experimental manipulations; alter experimental variables such as behavior (Morton and Griffiths 1985), drug dosing (Saranteas et al. 2004) and clearance; change the progress of a disease (Johnson et al. 2006); and contribute to morbidity and mortality. A variety of stressors can contribute to unintended distress, from postoperative pain or infection to barren housing conditions or the solitary confinement of an individual of a social species (Gunn and Morton 1995; Morton et al. 1993). Stereotypies, abnormal repetitive behaviors indicative of poor well-being (Garner et al. 2003) that are often observed in distressed animals, are thought to reflect defective brain function (Würbel 2001) and to be a result of poor animal welfare (Mason and Latham 2004). Stereotypies are thus likely to interfere with behavioral, neuroscience, and pharmacological studies.5
The impact of stress and distress on the quality of scientific research can result in the generation of compromised data, which in turn necessitates the use of more animals. This outcome is inconsistent with two of the
It should be noted that the negative connotations of stereotypies are not universally accepted. For further discussion see Chapter 3.