A break from the pups: The effects of loft access on the welfare of lactating laboratory rats

Abstract

Rats (Rattus norvegicus) bred for research are typically confined with their litters until weaning, but will spend time away from pups when given the opportunity. We aimed to assess how dam welfare is affected by the ability to escape from their pups. Rat dams (n = 16) were housed in cages either with or without an elevated loft. We measured time dams spent in lofts, time spent nursing, and affective states using elevated plus maze and anticipatory behavior testing. We predicted that 1) dams housed with lofts would use them increasingly as pups aged, 2) dams without a loft would spend more time passively nursing (i.e. initiated by pups rather than the dam) and more total time nursing as pups aged, and 3) dams housed with lofts would show evidence of a more positive affective state. Dams housed with lofts spent more time in the loft with increasing pup age; dams spent on average (mean ± SE) 27 ± 5% of their time in the loft when pups were 1 wk old, increasing to 52 ± 5% of their time at 3 wks. When pups were 3 wks old, dams with lofts spent less time passively nursing (10 ± 2% of total time, compared to 27 ± 4% for dams without a loft) and less time nursing overall (36 ± 4% of time versus 59 ± 2% for dams without a loft). Rats without loft access showed increased anticipatory behavior potentially indicative of negative affective state (24.5±1.8 behaviors per minute in wk 3 compared to 18.8±1.0 in wk 1). These findings indicate that rat dams in laboratories choose to spend time away from their pups when provided the opportunity, particularly later in lactation; an inability to do so is associated with increased passive nursing and negative affect.

Milking it for all it’s worth: The effects of environmental enrichment on maternal nurturance, lactation quality, and offspring social behavior

“…The efficaciousness of the “gold standard” housing cages in animal research has recently been called into question (Kentner et al, 2019b; Olsson & Dahlborn, 2002; Prendergast et al, 2014; Kentner et al, 2021). Results of the present study bolster the argument that EE housing conditions encapsulate a more naturalistic environment than SD, especially with regard to maternal behavior and development (Zhao et al, 2021; Connors et al, 2015; Ratuski & Weary 2021). Recent work has shown running wheel activity to alter milk quality in terms of specific inflammatory molecules such as leukocyte inhibitory factor, CXCL1, and CXCL2; however maternal care was not affected (Taki et al, 2020).…”

“…Again, SD dams were shown to spend more time on the nest than EE mothers (light: p>0.05, Figure 1I ; dark: X 2 (1) = 7.456, p = 0.006, Figure 1J ; total light + dark: X 2 (1) = 4.864, p = 0.027; Figure 1K ). During our maternal care observations, we did not plan to quantify “press posture” (Gaskill & Pritchett-Corning, 2015; Cramer et al, 1990; Ratuski & Weary 2021) but we subjectively noted its presence in SD dams when it was noticed during our study. A representative photo of this posture can be found in Figure 1C .…”

“…Additionally, EE dams have been shown to spend less time in a passive nursing posture compared to SD dams and demonstrate higher levels of the more effective active, or high arched back nursing posture (Connors et al, 2015; Strzelewicz et al, 2019). In another study, rat dams housed in cages with a loft that afforded an opportunity to periodically leave their pups also exhibited lower levels of passive nursing (Ratuski & Weary, 2021). This suggests that time away from the pups promotes maternal care efficiency upon returning to the nest.…”

Milking It for All It’s Worth: The Effects of Environmental Enrichment on Maternal Nurturance, Lactation Quality, and Offspring Social Behavior

“…The efficaciousness of the "gold standard" housing cages in animal research has recently been called into question (Kentner et al, 2019b;Olsson & Dahlborn, 2002;Prendergast et al, 2014;Kentner et al, 2021). Results of the present study bolster the argument that EE housing conditions encapsulate a more naturalistic environment than SD, especially with regard to maternal behavior and development (Zhao et al, 2021;Connors et al, 2015;Ratuski & Weary 2021). Given that EE animals do not display more phenotypic variability compared to those in standard housing (Kentner et al, 2021;Wolfer et al, 2004;Würbel, 2007;André et al, 2018)…”

Environmental Enrichment for Rats and Mice Housed in Laboratories: A Metareview

“…In the more immediate future, creative enrichment solutions that overcome or work within current practical limitations are called for. Some examples of more immediately feasible enrichment include altered food provision to allow for more natural foraging [ 52 ], the provision of get-away tunnels or lofts to allow for more natural maternal care when dams are housed with pups [ 163 , 164 ], combining existing cages to allow for more space and structural components in a housing system [ 165 , 166 ], repurposing of cages meant for larger species [ 167 ], repurposing of existing facility materials to make enrichment components [ 143 ], promoting positive human–animal interactions [ 168 , 169 , 170 ], and the use of temporary playpens in facilities that lack the space or resources to permanently house animals in more complex environments [ 3 , 43 , 171 ]. Notably, the environments of laboratory animals that are not used in experiments (e.g., breeding, training, or sentinel animals) could be improved with fewer constraints, given that they are not bound to experimental requirements [ 73 ].…”