Freymann, J., Tsai, P.-P., Stelzer, H. et al. 2017. The impact of bedding volumes on laboratory mice. Applied Animal Behaviour Science 186, 72-79.

Environmental refinement is considered to be an improvement in housing conditions for laboratory animals. Previous preference tests showed that female BALB/c and C57BL/6 mice prefer deeper bedding in comparison to shallow bedding (Freymann et al., 2015). In order to give a comprehensive insight into the impact of bedding depths on laboratory mice, we continued to examine the influence of three different bedding volumes (0.5l, 1.5l, 6l) on the preference of male mice (experiment 1), home cage behaviour (experiment 2) as well as body temperature, food intake, food conversion efficiency (gram food intake per gram weight gain), intra-cage ammonia and corticosterone levels (experiment 3) of females and males. Experiment 1 used an automatic system to assess the preferences of male BALB/c and C57BL/6 mice. The bedding volumes were tested in pairs, which resulted in three test conditions (A=0.5l vs. 1.5l; B=0.5l vs. 6l; C=1.5l vs. 6l). The results revealed significant preferences for cages containing large bedding volumes (test conditions A, B: p<0.0001 for both strains; C: p=0.0110 (BALB/c), p=0.0511 (C57BL/6)). The second experiment analysed the home cage behaviour of female and male BALB/c mice between 18:00 − 20:00 (CET) using instantaneous sampling. No significant differences regarding the behavioural patterns locomotion, grooming, agonistic interaction, feeding, drinking, nest-building, resting, digging and burrowing were detected. However, animals housed on shallow bedding (0.5l) engaged more in nest-building behaviour compared to groups housed larger volumes (1.5l or 6l). Experiment 3 demonstrated that bedding volumes (0.5l, 1.5l or 6l) have profound effects on mice’s physiology. BALB/c and C57BL/6 mice kept on deep bedding showed higher body temperatures (p<0.05 (0.5l compared to 1.5l, or 6l)), lower food intake p<0.01 (6l compared to 0.5l, or 1.5l) as well as reduced intra-cage ammonia levels compared to groups on shallow bedding. In addition a larger bedding volume increased food conversion efficiency and reduced corticosterone levels in female mice. The trend became particularly obvious in female BALB/c mice (p<0.05 (0.5l compared to 1.5l, or 6l) for both parameters). Our results underline the importance of a sufficient amount of cage bedding in the husbandry of laboratory mice.