Housing and husbandry standards in mice – the effects of social housing and testing order on experimental behaviour

We aim at enlarging the scientific basis for housing condition standards as crucial part of the experimental procedure in laboratory mice used as experimental animals in behavioural sciences. We investigate the effects of social- and non-social housing conditions, testing order, gender and strain on the animals’ experimental behaviour. Although it is known that experimental- and environmental conditions can affect experimental behaviour in mice (1), systematic studies on the nature of these effects are lacking. For male mice it is still under debate whether or not they should be housed singly or in groups, as their gender-specific territoriality might lead to inter-individual aggression (2). It can be hypothesised that experimental behaviour will significantly be affected by these social conflicts. On the other hand, mice are social animals which might suffer from isolation stress when housed individually.
In female mice, in which territoriality is limited to maternal defensive behavior, interindividual aggression is not to be expected. However, group-housed animals might communicate distress when exposed to a novel environment, which may explain reproted effects of testing order on experimental results (1). These potential impacts of testing order on experimental results might then be circumvented by testing only one animal per social group. Objectionably, as a consequence, the number of animals being used within one experiment will increase. Additionally, short-term isolation of group-housed animals during the experimental exposure might affect performance of the experimental animal as well.
We here focus on models of anxiety since inappropriate social housing conditions, which have to be considered as chronically stressful for the animals, will compromise the reliability of these models in particular, since stress is known to fundamentally influence emotionality. We compare the behaviour and peripheral stress hormone levels of single housed individuals with that of animals housed in social groups. Behavioural experiments are carried out in the modified hole board test, a test reliably monitoring various motivational systems in rodents, like anxiety-related behaviour, exploration, locomotor activity and social affinity (3).
Ultimately, we aim at defining the optimum social housing conditions for male and female mice of 3 frequently used strains. Next to providing more reliable results, the scientific evidence for standards on gender-specific housing conditions in mice will be enlarged.