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The response of C57BL/6J and BALB/cJ mice to increased housing density.

Year: 2010
Type: article
Abstract: Dear Editor, We are writing in regard to the article by Nicholson A and colleagues.3 We believe that the data presented do not support the primary conclusion drawn by the authors, namely, that housing density can be increased significantly over current Guide standards2 with few if any adverse effects. We also note that the conclusions stated in the abstract do not coincide with those in the text. The abstract states that the findings support a 50% to 100% increase over current Guide standards,2 whereas the discussion mentions a 30% to 50% increase. Although this may stem from confusion about the number of mice per cage versus the amount of floor space per mouse, it is an important distinction that requires clarification by the authors. Rather than supporting an increase in housing density, the data presented suggest that significant increases in density have adverse effects. A 100% increase above the current Guide standards2 appeared detrimental to the mice, based on criteria that the authors determined were most significant for determining wellbeing. These criteria included weight gain, adrenal gland size and percentage cortex, fecal corticosterone, in-cage telemetry of activity and heart rate, and behavioral aspects such as incidence of barbering and whisker-picking, fighting, and formal tests of anxiety. Many of these parameters changed with increasing density and were interpreted by the authors to be indicative of chronic stress or anxiety. Similar findings were reported by many of the papers cited in Figure 1 of the article.3 Thus, it is unclear why the authors would claim that housing density could be increased as much as 100% without affecting overall wellbeing. The validity of this conclusion is also called into question by the fact that the stated goal of the study was to serve as a preliminary experiment that would enable the testing of specific hypotheses in subsequent larger studies. The study was not designed to determine whether housing density could be increased; rather, the primary goal was to determine what parameters should be incorporated into future experiments. This tends to weaken any conclusions about housing density per se. The authors emphasize in the discussion that more extensive behavioral measurements are important to determining appropriate housing density. We strongly concur and would argue that simple strategies, such as monitoring for gross evidence of negative behavior (fighting, barbering, and whisker pulling), are necessary but not sufficient for assessing wellbeing. More refined behavioral testing would add substantially to understanding the optimal housing requirements for mice. Assessments of time budget, preference testing, and demand (how hard the animal will work to obtain the preference) would shed light on how animals use the space available to them. Behavioral measurements of anxiety in the presence of a strange setting or unknown animals would help clarify the extent to which high density housing is associated with stress responses. This topic was discussed in depth at the 2006 National AALAS meeting and later published in the November 2007 issue of Lab Animal.1 We believe for fairness to the reader and the laboratory animal community the author should reference this publication since in that forum similar studies from the same laboratory were criticized for weaknesses in experimental design and data interpretation. We would also point out that the issues at hand are not strictly scientific in their reach. There are ethical concerns and public perceptions that should influence the discussion. Providing sufficient space to permit species-typical activities and social interactions is an ethical imperative. Even if studies suggest that increased housing density is devoid of negative effects, implementation of high-density housing may lead to the public perception that animals are crowded into an unacceptably small space. This perception may well diminish public confidence in the proposition that the welfare of research animals is properly assured. Sincerely, Charmaine Foltz, DVM, DACLAM Director, Division of Veterinary Resources, National Institutes of Health David DeLong Chief, Veterinary Medical Unit, VA Medical Center (151)
Language: English
Open Access status: green
OpenAlex ID: W2175508254
FWCI:
Cites: 3
Cited by: 2
Related to: 10