Abstract
The review article of Alexandra L Whittaker et al. (pp 3–13) summarizes the current legal situation regarding minimal space allocation to mice and compares and discusses how variations in space may influence wellbeing of animals. It becomes evident that the issue is complex and depends on many factors, or is even controversial for an interpretation of whether an increase in space allocation is better. There are differences among directives and jurisdictions for the housing of animals. Yet, directives reveal a trend that as group size increases, space per animal is decreasing. Therefore, one of the important questions is, how such differences in housing, when correctly applied, influence research results and how comparable are such results between the different jurisdictions or animal facilities. By giving it a thorough reflection, when reporting on physiological parameters on a given number of animals, it becomes essential as to how many animals were housed together and specifics in space allocations need to be mentioned when publishing results.
Considerations for determining minimal space allowance need evidence-based animal welfare science. The title of the review article by itself is already challenging, how space and housing density influence measures of wellbeing; ‘wellbeing’ being defined as positive welfare outcomes. As also discussed in this review, allocating more space does not mean better welfare since mortality due to aggression may be higher. Our gut feeling would suggest that differences in space allocation and housing density might influence social behaviour, ranking with stress and anxiety, husbandry and reproduction, and underlying physiological parameters. This review makes clear that we are by far from having an answer with regard to how much minimal space is really needed. Yet, the question is pertinent for facility management with regard to economical questions, for legislation with regard to animal welfare or to satisfy public opinion, and for research with regard to reproducibility of research results.
Unfortunately, guidelines do not include suggested values for different stock and strains, but one can imagine that differences in minimal space available for an anxious or aggressive mouse strain will affect behaviour and physiological parameters, stress conditions, and reproduction. How far do epigenetic factors influence space requirements? Where do we have to set the limit for crowding or chronic stress? Eventually, setting space limits may require a fine-tuning for different stocks and strains. When investigating preferences for space, additional factors may also be of importance such as the types of bedding material or enrichment added to the cages.
In conclusion, this review raises an important question that may have important consequences for animal facilities, economy and legislation; and that more research in animal welfare science is needed to resolve the sometimes conflicting results. Defining minimal space allocation appears a challenging task that needs to consider many parameters and for the moment cannot be answered by a simple number of how much space to allocate to a mouse when housed individually in a group. This review also gives some ideas what needs to be investigated in order to determine the importance of space for mice. Furthermore, such a discussion on space requirements should be extended to other laboratory animal species where social behaviour governs the relationship and hierarchy between individuals.