Response, use and habituation to a mouse house in C57BL/6J and BALB/c mice

Abstract

Animal welfare depends on the possibility to express species-specific behaviours and can be strongly compromised in socially and environmentally deprived conditions. Nesting materials and refuges are very important resources to express these behaviours and should be considered as housing supplementation items. We evaluated the effects of one item of housing supplementation in standard settings in laboratory mice. C57BL/6JOlaHsd (B6) and BALB/cOlaHsd (BALB) young male and female mice, upon arrival, were housed in groups of four in standard laboratory cages and after 10 days of acclimatization, a red transparent plastic triangular-shaped Mouse House™ was introduced into half of the home cages. Animals with or without a mouse house were observed in various contexts for more than one month. Body weight gain and food intake, home cage behaviours, emotionality and response to standard cage changing procedures were evaluated. The presence of a mouse house in the home cage did not interfere with main developmental and behavioural parameters or emotionality of BALB and B6 male and female mice compared with controls. Both strains habituated to the mouse house in about a week, but made use of it differently, with BALB mice using the house more than the B6 strain. Our results suggest that mice habituated to the mouse house rather quickly without disrupting their home cage activities. Scientists can thus be encouraged to use mouse houses, also in view of the implementation of the EU Directive (2010/63/EU).

Fig. 1.

Experimental procedure. (A) Time line of experimental procedure. Salient events along over a month of study: body weight and food intake measures, behavioural observation periods, cage changes and videorecording times at different time points. Age (weeks) of the animals is also indicated. (B) Depiction of different time points/conditions at cage changing times when mice were observed and behaviours scored for 10 min. (C) Mouse house.

Fig. 2.

Body weight and food intake. (A-B) Body weight and (C-D) food intake, in respectively male and female mice of BALB and B6 strains with and without a mouse house measured before and after mouse house introduction. Data are expressed as mean ± SEM.

Fig. 3.

Behaviours observed right after cage changing. Percentage of behaviours performed outside or directed to the house in respectively (A-C) male and (B-D) female BALB and B6 mice observed at cage or mouse house changing times. (A-B) Day 1 and Day 18 clean mouse house in a dirty home cage. Day 12, dirty (C) or Day 32, clean (D) mouse house in a clean cage.

Fig. 4.

Behavioural profiles on day 1 vs day 18: clean house in a dirty cage. Percentage of behaviours scored in respectively (A) male and (B) female BALB and B6 mice observed upon first exposure to a clean mouse house (Day1) and to same cage/house condition on Day 18 of exposure. The percentage of behaviours performed outside the house (grooming, climbing to the roof of the cage, fighting, feeding or drinking) and the percentage of behaviours directed to the house (approach, contact, digging, on top, inside, through the doors) are shown.

Fig. 5.

Behavioural profiles on day 12 vs. day 32: dirty vs clean house in a clean cage. Percentage of behaviours scored in respectively (A) male and (B) female BALB and B6 mice observed upon exposure in a clean cage, to a dirty mouse house (Day12) and to a clean house on Day 32 of experiment. The percentage of behaviours performed outside the house (grooming, climbing to the roof of the cage, fighting, feeding or drinking) and the percentage of behaviours directed to the house (approach, contact, digging, on top, inside, through the doors) are shown.

Fig. 6.

Principal Components Analysis: Factor 2 and Factor 3 loadings. (A) Loadings for Factor 2 (9.45% of variance) that was interpreted as an “interest in the house” factor. ### P<0.0005 BALB vs B6, ANOVA. Data, from Supplementary Table 3, are expressed as mean ± SEM (n=3 cages per sex/strain). (B) Loadings for Factor 3 (4.38% of variance) that was interpreted as ‘habituation/approach to the house’ and varied over time, ***P<0.0001, ANOVA. Each point represents one cage (data from Supplementary Table 3).

Fig. 7.

Resting and contact with house behaviours. Frequency of resting behaviours (A-B) and contact with the mouse house (C) observed in male and female mice of BALB and B6 strains during the two weeks of habituation to the mouse house. Resting behaviour frequency was scored when occurring either in or out of the house (A-B). Data are expressed as mean (± SEM) frequency of contacts per week (C).

Fig. 8.

Emotionality (open field test). Percentage of time spent (A) or number of entries (B) in the centre of the open field in male and female mice of BALB and B6 strains exposed (House) or not exposed (No House) to a mouse house for about three weeks. Data are expressed as mean ± SEM.