Increased juvenile and adult body weights in BALB/cByJ mice reared in a communal nest.

Both wild and laboratory mice and rats preferentially rear their young in communal nests and indiscriminately nurse any of the young within the nest. In this study, BALBc/ByJ mice reared under communal nesting (CN) conditions (3 dams and their litters sharing a common nest) were compared with BALBc/ByJ mice raised in single (one dam with her litter) nests (SN) in body weight from birth into adulthood; food and water intake and body composition were compared between adult mice. Compared with SN female mice, female CN mice (measured only until weaning) exhibited significantly higher body weights at postnatal days 11 and 25. Male CN mice were significantly heavier than were male SN mice at postnatal day 25 and at 20, 26, and 30 wk of age. There were no differences between adult male mice from CN and SN groups in 48-h food and water intake or body composition (total lean:total fat ratio; measured by quantitative MRI). In conclusion, BALB/cByJ mice reared under communal nesting conditions showed more robust juvenile growth rates than did mice raised with a single dam and litter per cage. In addition, body weights of male CN mice remained higher than male SN mice into adulthood. Copyright 2011 by the American Association for Laboratory Animal Science