Clinical examination to establish the presence of distress should focus on, but not be limited to, the following: signs of abnormal respiration (shallow, labored, or rapid); assessment of grooming and hair coat (piloerected or greasy, possibly reflecting reduced grooming); examination of the eyes (runny, glassy, or unfocused); examination of motor postures (hunching or cowering in the corner of the cage, lying on one’s side, lack of movement with loss of muscle tone); absence of alertness or quiescence (inattention to ongoing stimuli); changes in body weight; the ability or failure to produce urine or feces; unusual features of urine (volume, smell, and color) or feces (quantity, consistency, and color); the presence of vomit; the status of the animal’s appetite and water intake; and intense or frequent vocalizations (Bennett et al. 1998; Fortman et al. 2002; Fox et al. 2002). It is appropriate to evaluate some of these signs in context, as, for example, rapid breathing could result from vigorous activities such as playing or running on the wheel, lying down may occur as part of social grooming (e.g., among macaques), weight loss is often associated with advanced age, and some mammals raise their hair (piloerection) while eating. In addition, clinical evaluation and diagnosis should consider species, age, gender, physiological state, and genetic variables (Bennett et al. 1998).
While some of the clinical signs described above (e.g., respiratory changes, changes in fecal material and/or in urine) are more relevant to the acute onset of a distressful state, other measures may serve as potential early warning signs of distress (e.g., rapid body weight changes in the absence of dietary modifications). Significant and unexpected changes in weight in either direction may be indicators of altered endocrinological, immunological, or neurological parameters. Indeed, the relatively sudden loss of 25% body weight of a nonhuman primate is one of the parameters used to determine humane endpoints in primate research (Association of Primate Veterinarians 2008).
This view should not be applied to caloric restriction research protocols where animals may be subject to controlled diets that reduce their weight by as much as 15-20% (Heiderstadt et al. 2000). Such protocols are widely used in gerontology research where diet has been shown to slow aging, extend lifespan, and reduce the incidence of age-related diseases in rodents (Goto et al. 2002; for more references see Additional References), while beneficial effects have also been observed in nonhuman primates (Ingram et al. 2007). Moreover, sensory-motor function and learning studies may use caloric or water restriction as a motivational tool (Heiderstadt et al. 2000; Smith and Metz 2005). In these studies regular monitoring of body weight is essential to ensure that animals either do not fall below an accepted weight