Postweaning Grouping as a Strategy to Reduce Singly Housed Male Mice

Abstract

Rearing laboratory mice in groups is important since social isolation after weaning induces brain alterations, which entails behavioral abnormalities in adulthood. Age is an important factor when grouping males of different litters due to inter-male aggressiveness. The aim of this study was to determine whether newly weaned mice could safely be grouped with late juvenile or early and late pubescent mice, and whether cage cleaning, the number of the hosting group members and testosterone plasma levels have any influence. Newly weaned C57BL/6J, CD1, and SCID Beige male mice were systematically grouped with same strain late juvenile, early or late pubescent male mice in clean or dirty cages of 1, 2 or 3 hosting members. We also analyzed plasma testosterone levels at different postnatal days. Our result showed that only strain and hosting male's age influence agonistic behavior toward newly weaned mice. Thus, in order not to house a recently weaned male alone, we would recommend grouping it with late juvenile same strain mice in all studied strains. In the same way, CD1 and SCID Beige pubescent mice will admit a newly weaned mouse in their group. However, we would not recommend grouping newly weaned and pubescent C57BL/6J males.

Keywords: aggressiveness; juvenile; mouse; pubescent; testosterone.

Figure 1

Number of cages in which wound due to fights were observed; (a) C57BL/6J (b) CD1 and (c) SCID Beige newly weaned mice after grouping with late juvenile male mice. X-axis shows the condition of the cage, clean or dirty. Z-axis shows whether there were or were not wounds due to fights. White bars indicate cages with one member; grey bars two members and black bar three members’ cages. A total of 30 cages per strain were analyzed, five cages per condition.

Figure 2

Number of cages in which wound due to fights were observed: (a) C57BL/6J, (b) CD1, and (c) SCID Beige newly weaned mice after grouping with early pubescent male mice. X-axis shows the condition of the cage, clean or dirty. Z-axis shows whether there were or were no wounds due to fights. White bars indicate cages with one member, grey bars two members, and black bar three members’ cages. A total of 30 cages per strain were analyzed—five cages per condition.

Figure 3

Number of cages in which wound due to fights were observed: (a) C57BL/6J (b) CD1, and (c) SCID Beige newly weaned mice after grouping with late pubescent male mice. X-axis shows the condition of the cage, clean or dirty. Z-axis shows whether there were or were no wounds due to fights. White bars indicate cages with one member; grey bars two members and black bar three members’ cages. A total of 30 cages per strain were analyzed—five cages per condition.

Figure 4

C57BL/6J, CD1, and SCID Beige testosterone plasma level (ng/mL) at different postnatal days. Data are expressed as mean ± SEM. We analyzed 10 animals per strain and age.