Male management: coping with aggression problems in male laboratory mice

In a laboratory environment, aggressive interactions between male mice may exceed normal levels leading to negative effects both on the well-being of the animals and on the validity of experimental results. In this paper we review results from the literature and our own research with regard to coping with excessive aggressive behaviour in male laboratory mice. Based on this review practical recommendations concerning the housing and care of male laboratory mice are formulated. In short, it is recommended to avoid individual housing, to transfer odour cues from the nesting area during cage cleaning and to apply nesting material as environmental enrichment. Furthermore, group size should be optimized to three animals per cage. Further research, in particular into the effects of frequency, duration, type and severity of disturbances during an experiment on the degree of aggression, is recommended.

The importance of learning young: the use of nesting material in laboratory rats

Unlike mice, adult laboratory rats do not spontaneously build nests when nesting material is offered. As a result, nesting material is often regarded as unsuitable environmental enrichment for laboratory rats. Wild rats and pet rats, however, have been observed to build complex nests from nesting material at hand. It was hypothesized that nest building in rats is an acquired behaviour, rather than genetically predisposed. To test this hypothesis, the progeny of three Wistar rats provided with nesting material (Kleenex tissues) during pregnancy and three standard-housed rats were divided in 34 same-sex couples with access to nesting material: (1) from the age of 8 weeks ( n=7); (2) from weaning ( n=8); (3) from birth ( n=17). The latter were subdivided into two groups after weaning, one provided with Kleenex tissues ( n=9), the other with Enviro-dri ( n=8). At the age of 12 weeks, all couples were provided with both types of nesting material for one week. Amount, shape, and soiling of the nesting material were scored on weekdays, and behaviour of the rats was scored twice weekly. Results indicated that the older the rats were when first provided with nesting material, the greater the amount of nesting material eaten and soiled, and the nests built were less elaborate. Overall, Enviro-dri was eaten less than Kleenex tissues. It is concluded that rats need to learn the proper use of nesting material. When provided from birth, nesting material is a suitable type of environmental enrichment for laboratory rats.

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.

How to improve housing conditions of laboratory animals: the possibilities of environmental refinement

Housing systems for captive animals have often been designed on the basis of economic and ergonomic considerations, such as equipment, costs, space, workload, ability to observe the animals and to maintain a certain degree of hygiene, with little or no consideration for animal welfare. Environmental refinement can be defined as any modification in the environment of captive animals that seeks to enhance the physical and psychological well-being of the animals by providing stimuli which meet the animals' species-specific needs. This article provides an overview of environmental factors that influence the well-being of captive animals with specific reference to the needs of the most common laboratory species. It is important to evaluate environmental refinement in terms of the benefit to the animal, by assessing the use of and preference for certain enrichment, the effect on behaviour, and the performance of species-typical behaviour on physiological parameters. It is also necessary to evaluate the impact of refinement on scientific outcome, including whether and how statistical power is affected. Communication and team work between animal welfare scientists, animal research scientists, institutional animal welfare officers, veterinarians and animal ethics committees, animal facility management and personnel, are essential for success.

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.

Preference for social contact versus environmental enrichment in male laboratory mice

Due to their aggressive nature, male mice are less frequently used than female mice in biomedical research. When aggressive males are being used, individual housing is common practice. The question arises whether this is an acceptable housing for a social species. The present study was designed to gain more insight into the nature of inter-male social contact and into the potential of a form of environmental enrichment (nesting material) to compensate for the lack of social contact. In a series of tests, we analysed whether male mice of different ages preferred to spend time (1) near a familiar cage mate versus an empty cage, or (2) near to a familiar cage mate versus direct contact with nesting material (tissues). Dwelling time in each of the test cages and sleeping sites was recorded, as was the behaviour of the test mice. Results indicated that when other conditions were similar, male mice preferred to sleep in close proximity to their familiar cage mate. Furthermore, the need to engage in active social behaviour increased with age. Tissues were used to a large extent for sleeping and sleep-related behaviour. It is concluded that single housing in order to avoid aggression between male mice is a solution with evident negative consequences for the animals. When individual housing is inevitable due to excessive aggressive behaviour, the presence of nesting material could partly compensate for the deprivation of social contact.