Hang on: an evaluation of the hemp rope as environmental enrichment in C57BL/6 mice

Abstract

When introducing environmental enrichment in laboratory animals, positive and/or negative effects on behavioural and physiological parameters should be evaluated. This three-step randomised controlled trial in male C57BL/6 mice investigated the effect of supplementing the environment with one or more hemp ropes. In part 1, the effect of a hemp rope on aggressive and social behaviour, stress and anxiety levels was assessed by social interaction test, elevated plus maze behaviour, and faecal corticosterone metabolites, respectively (n = 224 mice). In part 2, the effect of 1, 2 or 7 hemp ropes on aggressive behaviour in mice subjected to routine handling was evaluated by assessing the number of wounded companion animals and wounds per animal (n = 224). In part 3, climbing activity in the rope and amount of material shredded from the rope was assessed (n = 56). Mice housed with one hemp rope engaged in social behaviour for longer time than mice housed without a hemp rope, while no difference was detected in stress and anxiety levels. No difference was seen in the number of wounded animals or wounds per animal when adding 1, 2 or 7 hemp ropes to the existing environment in mice undergoing minimal human handling. The mice continuously shredded and climbed the rope, even when provided with a new rope, although time spent climbing decreased slightly over time. Thus, a hemp rope can be used as additional environmental enrichment amongst male C57BL/6 mice.

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

“…It is possible that previous studies have failed to provide sufficient quantities of enrichment to mitigate competition [ 140 ]. While there are many examples of structural enrichment resulting in increased aggression among males (e.g., [ 141 , 142 ]), there are also many cases of successful enrichment use (involving a range of genetic strains and enrichment strategies) [ 143 , 144 , 145 , 146 , 147 ]. In one example, male mice housed with hemp ropes hanging from the cage lid demonstrated more aggression when frequently tail-handled by experimenters; when handling was reduced, mice housed with hemp ropes showed no differences in aggression compared to the conventionally housed control group [ 145 ].…”

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“…Sit experiments were performed on the mice as described in the literature. 23 The mice were placed in a separate measuring cage and allowed to explore freely for 120 min. A male juvenile mouse (4–5 weeks old) was then placed in a cage to record the time spent socializing between them during the test.…”

Effects of temporary access to environmental enrichment on measures of laboratory mouse welfare

“…Escalated aggression is an acute welfare concern 12 and repeated aggressive encounters can cause chronic stress for subordinate mice 14 , perhaps especially in shoebox cages where mice are unable to physically escape and thus de-escalate interactions. Laboratory mice housed in shoebox cages may behave aggressively as a result of heightened responses to stressful stimuli such as cage changing 15 or tail handling 16 , although these effects are more commonly studied in males. Deficient housing conditions have also been linked to increased fear or anxiety behaviour, with additional effects on stress hormones and immune responses 17 ; these effects are concerning for animal welfare and for their potential impact on experimental outcomes.…”