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Several confounding factors may influence the outcome of an experiment and the extent of inter-individual variation. The aim of this study was to investigate if cage enrichment induces an effect on experimental mean values and on inter-individual variation in the light/dark paradigm using diazepam as the anxiolytic drug. The behaviour of 216 naive adult male mice of two different strains (BALB/c and C57BL/6) was studied. The animals were housed in groups of four in 'non-enriched', 'enriched' (nesting material) or 'super-enriched' (nest-box, nesting material, wooden gnawing stick and PVC tube) cages. After 5 weeks the animals were assigned to one of three treatments: control (no injection), sham (saline injection i.p.) or diazepam (1 mg/kg bw i.p.) and tested in the light/dark test for 5 min. Variation data were analysed using three different methods (mean absolute deviation, coefficient of variation and power analysis). The C57BL/6 mice scored higher than BALB/c mice in activity related measurements and showed a less 'emotional' behaviour profile in the pharmacological control situation of the light/dark test. In this study the anxiolytic effect of diazepam was clear in BALB/c mice but absent in C57BL/6 mice. Mice housed in enriched and super-enriched cages gained more weight than mice in non-enriched cages, although food intake was not affected. Generally, the strain of mouse had the greatest impact on both mean values and variation. However, there was no consistent increase for one particular strain. The choice of statistical method for analysing variation may influence the interpretation of within-group variability, but none of the methods showed any significant differences between standard and enriched conditions on variability in any of the parameters measured

Activity. --- Adult. --- Analysis. --- Animal-models. --- Animal. --- Animals. --- Anxiety. --- Behavior. --- Behaviour. --- Cage. --- Choice. --- Control. --- Diazepam. --- Drug. --- Enriched. --- Enrichment. --- Environmental enrichment. --- Experiment. --- Food intake. --- Food. --- Group. --- Housing,exploration,activity,emotionality,laboras,mice. --- Inbred strains. --- Increase. --- Laboratory mice. --- Light/dark test. --- Male-mice. --- Male. --- Method. --- Mice. --- Mouse. --- Nest box. --- Nesting material. --- Parameters. --- Preferences. --- Pvc. --- Rats. --- Test. --- Treatment. --- Validation. --- Variability. --- Variation. --- Weight.

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This study focused on the effects of different enriched environments for mice in a number of behavioral and physiological parameters in two routine laboratory testing procedures -- potency testing for tetanus vaccine and stress induced hyperthermia. The variability in the results was studied by calculating and analyzing mean absolute deviations. Mice from enriched conditions weighed more and consumed more food than mice from standard housing conditions. However, mice from enriched conditions lost more body weight after being housed individually. Other physiological parameters showed no differences. Mice from standard conditions were more active in an open field, suggesting a tendency to over-respond to various stimuli in a testing environment. Mice from enriched environments were more tranquil and easier to handle. The enrichment did not influence the variability in any of the parameters measured, although earlier results and results of other authors suggest that the effects on the variability in results are parameter dependent. When enrichment does not influence variability, there is no reason for not introducing cage enrichment and by doing so contributing to the animals' welfare.

Animal. --- Animals. --- Body weight. --- Body-weight. --- Cage. --- Enriched environment. --- Enriched. --- Enrichment. --- Environment. --- Environmental enrichment. --- Environments. --- Field. --- Food. --- Housing conditions. --- Housing. --- Hyperthermia. --- Laboratory. --- Mice. --- Open field. --- Open-field. --- Parameters. --- Physiological. --- Potency. --- Stimuli. --- Stress. --- Variability. --- Variation. --- Weight. --- Welfare.

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From welfare perspective group housing of mice is preferred over individual housing. Group housing of male laboratory mice, however, often leads to problems due to excessive aggressive behaviour. In our search for management and housing modifications to decrease aggression in group-housed male laboratory mice, we have tested the effect of two types of environmental enrichment--nesting material and shelter--on aggressive behaviour after cage cleaning and after a 1 h isolation period. Severity of wounds, urinary corticosterone levels, body weight, food and water intake and several post-mortem parameters were also monitored. The results indicated that type of enrichment strongly affected both aggressive behaviour and physiological parameters. Overall, nesting material reduced aggressive behaviour, while a shelter increased aggressive behaviour compared to control housing. This effect was also reflected in the number of wounds counted. Furthermore, during shelter housing mice gained less body weight, drank less and showed higher corticosterone levels, while in housing conditions with nesting material, mice ate less. We conclude that providing male mice with nesting material reduces aggression between male mice, and may, thus, be promoted as being beneficial to their physical health and psychological well-being.

Aggression. --- Aggressive. --- Behaviour. --- Body weight. --- Body-weight. --- Cage. --- Cleaning. --- Control. --- Corticosterone. --- Enrichment. --- Food. --- Group housing. --- Group. --- Health. --- Housing conditions. --- Housing. --- Individual housing. --- Isolation. --- Laboratory mice. --- Laboratory. --- Level. --- Male-mice. --- Male. --- Management. --- Mice. --- Nesting material. --- Parameters. --- Physical. --- Physiological. --- Psychological well-being. --- Search. --- Shelter. --- Stress. --- Weight. --- Welfare. --- Well-being.

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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

Activity. --- Adrenal tyrosine hydroxylase. --- Adrenal. --- Aggression. --- Aggressive-behavior. --- Aggressive. --- Behaviour. --- Body weight. --- Body-weight. --- Cage. --- Cages. --- Chronic stress. --- Cleaning. --- Corticosterone levels. --- Corticosterone. --- Cues. --- Enriched. --- Environmental enrichment. --- Experience. --- Experiment. --- Experiments. --- Food. --- Group. --- Husbandry. --- Inbred strains. --- Laboratory mice. --- Laboratory. --- Level. --- Long-term. --- Male dba/2j mice. --- Male laboratory mice. --- Male mice. --- Male-mice. --- Male. --- Mice. --- Modulation. --- Mouse. --- Nesting material. --- Olfactory cues. --- Olfactory. --- Parameters. --- Physiological. --- Provision. --- Rats. --- Stress. --- Test. --- Time. --- Tyrosine-hydroxylase. --- Tyrosine. --- Urine. --- Weight. --- Welfare.