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.</p

Nesting material as environmental enrichment has no adverse effects on behavior and physiology of laboratory mice

Environmental enrichment may improve the quality of life of captive animals by altering the environment of animals so that they are able to perform more of the behavior that is within the range of the animal's species specific repertoire. When enrichment is introduced into an animal's environment, it is important to evaluate the effect of the enrichment program and to assess whether the animal continues to use the enrichment in the long-term. Groups of mice were housed under either standard or enriched conditions for several weeks. Nesting material which was highly preferred in previous studies was used as enrichment. During the period of differential housing several behavioral parameters (behavioral tests and handling) and physiological parameters (urine and plasma corticosterone, food and water intake, body and adrenal weight) were monitored to determine the impact of environmental enrichment. Observations were made to determine whether or not the mice continued to use the enrichment. The results indicated that throughout the study all mice used the nesting material to build nests and that mice from enriched conditions weighed more than mice housed under standard conditions, although the latter consumed more food. No major differences for behavioral and physiological parameters were found between the groups of mice housed under different conditions. Therefore it is not likely that supply of nesting material will jeopardize the outcome of experiments. (C) 1997 Elsevier Science Inc

Modulation of aggression in male mice: Influence of cage cleaning regime and scent marks

Group housing of male laboratory mice often leads to welfare problems due to aggressive behaviour. From a welfare perspective, individual housing is not a preferred solution to these problems - and so we sought other ways of reducing aggression between male mice. Aggression peaks after disturbances such as cage cleaning. Transfer of olfactory cues during cage cleaning procedures has been repeatedly proposed as a means of reducing these peaks in aggression. In this study, the aggression-modulating properties of olfactory cues were studied by investigating the effects of their source and distribution on aggression after cage cleaning in groups of male BALB/c mice. The physiological effects of aggression on individuals within a group were also monitored. Our results indicated that neither kinship nor distribution of urine marks affected aggression. Olfactory cues from nesting and bedding material, however, affected aggression to a marked degree: transfer of nesting material reduced aggression significantly, while transfer of sawdust containing urine and faeces seemed to intensify, aggression. None of the physiological data revealed any differences between dominant and subordinate animals, nor any correlations with aggressiveness, except that dominant animals gained weight more rapidly than subordinate ones. We conclude that the transfer of nesting material will reduce aggression, or at least slow down its development, and thus aid the reduction of social tension due to cage cleaning

Preferences for nest boxes as environmental enrichment for laboratory mice

In nature, mice live in burrows with nest chambers where they breed and may hide from predators. In the laboratory, a shelter or refuge is an easily applicable form of enrichment which may enhance the welfare of laboratory mice by giving them more control over their environment. Six nest boxes made of different materials were evaluated in a preference test with male and female mice of two strains (C57BL/6J and BALB/c). In general, mice showed a preference for cages with a nest box made of grid metal as compared to clear or white perspex nest boxes, or no nest box. They also showed a preference for a cage with a nest box of perforated metal as compared to nest boxes made of grey PVC or sheer metal, or no nest box. When offered a nest box with one open side or a nest box with two open sides, most mice preferred the nest box with one open side and were observed to lie in it with their heads directed towards the opening. The results of this study show that nest boxes may be used for enrichment purposes in caged mice, although it is not yet entirely clear what are the main features influencing the animals' preferences. When providing nest boxes as shelters, the structure and design of this type of enrichment should be taken into account, because these may have an effect on the social structure of groups of mice