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.

Fig 1. Experimental timeline for anticipatory behavior (AB), elevated plus maze (EPM) and maternal behavior data collection.

“Training” refers to anticipatory behavior conditioning, while “habituation” refers to initial exposures to the experimenters, the elevated plus maze, and removal of lofts for rats in the no loft treatment. Time is shown relative to the day pups were born (Post-natal day, PND, 0).

Fig 2. Mean time spent in the loft per week, expressed as a percentage of observational scans, for rats with loft access.

The large black points and vertical bars depict least-square (LS) means and standard errors from the model output; smaller colorful points show the means of individual rats (n = 9 rats).

Fig 3

Mean time rats spent nursing per week, shown separately for A) active nursing, B) passive nursing, and C) total nursing. Results are shown separately by treatment, with 9 rats in the loft treatment and 7 rats in the no loft treatment. Plot depicts the LS means and standard errors from the model output.

Fig 4. Correlation between total nursing time and loft use.

Only rats from the loft treatment are shown. Each point represents the mean value for each rat (n = 9); individual rats are shown using different colours.

Fig 5. Behavioral transitions per minute during anticipatory behavior testing.

Rats were assessed for this behavior twice per week and results were analyzed as weekly means. Results are shown separately by treatment. Plot depicts the LS means and standard errors from model output; n = 16 rats (9 in the loft treatment and 7 in the no loft treatment).

Fig 6. Mean time spent in the open arms during the elevated plus maze test.

Rats were tested once per week over the pup rearing period. Results are shown separately by treatment with 9 rats in the loft treatment and 7 in the no loft treatment. Plot depicts the LS means and standard errors from the model output.