Short-term effects of a disturbed light–dark cycle and environmental enrichment on aggression and stress-related parameters in male mice

In the laboratory setting, environmental factors have a major influence on the well-being of laboratory animals. The present study shows the importance of a semi-natural light–dark cycle. In this experiment one cohort of mice was kept with a continuous lighting for one week. After the first week the artificial light–dark cycle was 12:12 with lights on at 07:00 h. The second cohort of mice was kept with this 12:12 h light–dark cycle from the start. Half of each cohort received environmental enrichment. In order to analyse corticosterone levels, urine samples were collected. To measure agonistic behaviour, the behaviour of the mice was recorded on videotape immediately after cage cleaning. A significant difference in corticosterone levels between cohorts was found during disturbed lighting, but not after lighting conditions were reset to 12:12 h. In the first test week, mice subjected to disturbed lighting also showed a significantly shorter agonistic latency than control mice. This difference had disappeared when in the second test week all mice experienced 12:12 h lighting. No effects of enriched housing were found. This experiment has shown that disturbed lighting for socially-housed male mice caused physiological and behavioural changes indicative of stress, not only leading to much higher levels of corticosterone but also to shorter agonistic latency within the groups.

Long-term effects of husbandry procedures on stress-related parameters in male mice of two strains

In socially unstable groups of male laboratory mice, individuals may experience a chronic stress situation. Previous experiments have shown that the transfer of specific olfactory cues during cage cleaning, and the provision of nesting material decrease aggression and stress in group-housed male mice. In this study, the combined effect of these husbandry procedures were tested for their long-term effect on stress in groups of moderately aggressive (BALB/c) and severely aggressive (CD-1) male mice. The physiological and behavioural stress-related parameters used were body weight, food and water intake, spleen and thymus weight, adrenal tyrosine hydroxylase activity, urine corticosterone levels and behaviour in a cage emergence test. Long-term provision of nesting material and its transfer during cage cleaning was found to influence several stress-related physiological parameters. Mice housed in cages enriched with nesting material had lower urine corticosterone levels and heavier thymuses, and they consumed less food and water than standard-housed mice. Furthermore, marked differences were found between strains. CD-1 mice were less anxious in the cage emergence test, weighed more, ate and drank more, and had heavier thymuses but lighter spleens and lower corticosterone levels than BALB/c mice. We conclude that the long-term provision of nesting material, including the transfer of nesting material during cage cleaning, reduces stress and thereby enhances the welfare of laboratory mice.