Four-week individual caging of male ICR mice alters body composition without change in body mass

Abstract

Understanding the physiological implications of caging conditions for mice is crucial in improving the replicability and reliability of animal research. Individual caging of mice is known to alter mouse psychology, such as triggering depression-like symptoms in mice, suggesting that caging conditions could have negative effects on mice. Therefore, we hypothesized that individual caging could affect the physical composition of outbred mice. To investigate this, dual X-ray absorptiometry (DXA) was used to compare the mass, bone mineral content (BMC), bone mineral density (BMD), lean tissue percentage and fat tissue percentage between group and individual caged mice. We also conducted open field test to compare mouse activities in different caging conditions. Our results showed significantly reduced BMD and lean tissue percentage and significantly increased fat tissue percentage in individually-caged male mice. Furthermore, there were no differences in body mass and activity between the grouped and individual mice, suggesting that these physical alterations were not induced by group-related activity. In this study, we conclude that individual caging could alter the body composition of mice without affecting external morphology.

Individual housing of male C57BL/6J mice after weaning impairs growth and predisposes for obesity

“…The data from the current study suggests that individual housing of mice at these standard temperatures may lead to even further deviation from human physiology and should therefore be regarded as an additional limitation to the translational value of such mouse research models. Moreover, the results from this and other studies (8, 35) show that the metabolic derangements observed in individually versus socially housed mice are not always reflected in higher body weights. This stresses that potential confounding influences of environment on mouse physiology may remain unnoticed when only body weight is monitored.…”

“…Basal CORT levels were however not affected during adolescence due to individual housing (but see below). As (home cage) physical activity levels were not monitored in the current study, a potential contribution of that factor to the differences in fat deposition observed between individually and socially housed mice in the current study cannot be excluded, although such an effect may be unlikely (35). It remains unknown whether the increased adiposity in individually housed mice may be of functional relevance to the animal.…”

“…Whereas the reduced body weight due to individual housing is transient, the reduced bone length and width persist into adulthood. Bone length in mice typically correlates to growth rate between 3 and 5 weeks of age (33), but as changes in bone mass and bone mineral density have also been reported in mice that were individually housed from adult age onwards (34, 35), reduced mechanical loading (i.e. reduced physical interaction, play, fighting) may also contribute to the shorter bone length in individually housed mice compared to socially housed mice.…”

Individual housing of male C57BL/6J mice after weaning impairs growth and predisposes for obesity

“…Whereas the reduced body weight due to individual housing is transient, the reduced bone length and width persist into adulthood. Bone length in mice typically correlates to growth rate between 3 and 5 weeks of age [41], but as changes in bone mass and bone mineral density have also been reported in mice that were individually housed from adult age onwards [10,42], reduced…”

“…Moreover, based on the results of a systematic review and meta-analysis we recently conducted [8], we concluded that individual versus social housing of rats and mice alters metabolic health status. For instance, individually housed mice show increased energy intake and altered adipose tissue deposition compared to socially housed mice, thought the extent to which this occurs may be sensitive to strain, diet and other environmental factors [9][10][11][12]. Social isolation stress may indeed affect the neurobiological control of food intake by affecting brain area's involved in energy balance regulation such as the hypothalamus [13,14] and the reward system [15].…”