Leaving home: A study of laboratory mouse pup independence

Abstract

a b s t r a c tJuvenile wild house mice leave their mothers at 8 weeks (+). In contrast, laboratory strains of mice (lab mice) are typically 'weaned' at postnatal day (PND) 21. Lab mice might mature faster than their wild forebears; but if they do not, standard laboratory weaning likely involves maternal deprivation. We therefore investigated when lab mice voluntarily leave their mothers. C57BL/6J families were housed in home cages (HC) each attached via a tunnel to an identical 'dispersal cage' (DC); tunnel-widths allowed pups but not dams to pass. For generality, we used two common cage-types: Ancare 'shoe-boxes' (28 cm × 19 cm × 13 cm) and Thoren 'duplexes' (30 cm × 14 cm × 14 cm). Measures of pup independence were recorded PND 16-35. Pups first visited the DC at PND 21.5 ± 0.35; utilised its food/nesting material at PND 22.6 ± 1.5; and DC-use increased up to PND 35. However, maternal care continued and even at PND 35, pups spent at least 50% of their time with mothers. This differed between cage-types: 'shoe-box' mice matured faster (P < 0.01), becoming indifferent between the HC and DC by PND 35; while same aged 'duplex' mice preferred the HC, and received more maternal care (perhaps because they weighed less). Thus, similar to wild house mice, lab mouse independence occurs weeks after PND 21; independence is also plastic, affected by the local environment. 'Weaning' lab mouse pups at PND 21 therefore deprives them of maternal care, to an extent varying between different widely used cage-types. The impact this has on stress, abnormal behaviour, brain development, and inter-lab variation now needs investigating.

The complex ontogenetic trajectory of mandibular shape in a laboratory mouse

“…; Sale et al. ); W, end of weaning (König & Markl, ; Bechard & Mason, ); R, earliest age of first reproduction or dispersal of wild Mus (Gerlach, ; Krackow, ).…”

Effects of weaning age and housing conditions on phenotypic differences in mice

“…While the effects of early weaning compared to standard weaning are reasonably well described, far fewer studies have compared the effects of late weaning (up to day 35) to standard weaning [27][28][29] . Mice weaned on day 28 or 35 were behaviorally www.nature.com/scientificreports/ less anxious in the open-field and elevated plus maze, with concordantly lower levels of corticosterone secretion, and displayed less social behavior in social interaction tests [27][28][29] . In contrast to the effects of weaning age, our results on the effects of single housing compared to group housing are reasonably consistent with other studies 35,[61][62][63][64][65][66][67][68] .…”

“…Under naturalistic conditions, physiological and behavioral changes related to weaning in mice occur between postnatal days 14 and 17, with decreases in food intake and pup-directed behavior by the dam, and a transition to the eating of solid food by the pups 23 – 25 . Weaning typically ends around postnatal day 23 23 – 25 , but depending on the litter size can extend until postnatal day 30–35 26 – 29 .…”

“…In addition to the timing of weaning, the process of weaning itself differs between the natural condition and the routine in breeding facilities. Under natural conditions, weaning is a gradual transitionary process occurring over several days to weeks, while weaning in breeding facilities is characterized by the instant and permanent separation of the offspring from the mother at a pre-set day; usually around postnatal day 21 29 .…”

Extensive juvenile “babysitting” facilitates later adult maternal responsiveness, decreases anxiety, and increases dorsal raphe tryptophan hydroxylase‐2 expression in female laboratory rats

“…Because of the delayed implantation characteristic of postpartum insemination (Gilbert et al, 1983;Mantalenakis & Ketchel, 1966), and that many juvenile rats do not disperse from their natal nest until after their younger siblings are born (Calhoun, 1963), juveniles would have ample opportunity to interact with neonates (Gilbert et al, 1983;Stern & Rogers, 1988;Uriarte et al, 2008). The paradigm in Experiment 2 is also more naturalistic than that used in Experiment 1 because weaning in rats and other animals is not normally an abrupt event (e.g., Galef, 1981;Bechard & Mason, 2010), despite standard protocol in many laboratories including our own for most studies. Unlike Stern and Rogers (1988), we found no significant effect of juvenile alloparental experience with younger siblings on the later maternal responsiveness of the older sisters.…”