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Brief communication

Modifying environment for laboratory mice and rats may enhance their welfare.

Environmental design for laboratory animals addresses ergonomic and economic needs rather than animal welfare needs (Van de Weerd et al., 1997, Sherwin & Glen 2002, Augustsson 2004, Baumans 2004). A way to enhance the environment is to use enrichment (EE); improvement of the biological functioning of captive animals resulting from modifications to their environment. Thus enriched housing conditions allow animals to display a more extensive repertoire of species specific behaviours and may provide appropriate stimulation to facilitate coping with physical and ethological needs (Van de Weerd et al., 1997, Van der Harst et al ., 2002).

The animal needs and species specific behaviours should be addressed when designing housing for laboratory rodents. Kleneex is show to be highly appreciated as nesting material (Van de Weerd et al., 1997, 1998); it gives mice an opportunity to perform species specific behaviours and the potential for manipulation.

In this study nesting material was introduced as enrichment to mice and foraging enrichment to rats and investigated to see the impact on the animals, with emphasis on anxiety, exploration and long term effect.

In experiment I, female mice were placed in enriched housing system containing nesting material, or control cages. Mice behaviour in home cage was observed during two periods with one week in between to determine if the enrichment was still being used. Risk assessment and anxiety behaviours were observed in an open field test. During experiment II, enrichment in the shape of a maze, was introduced to male rats. The observation procedure was performed in the same way as in experiment I. Food was placed in the corners of the maze; the control cages were provided food ad libitum.

During the second period the mice was seen climbing and digging more while nesting, grooming, feeding and sleeping were performed more in the first period. Given that climbing and digging is considered stereotypic behaviours, it is not surprisingly. No stereotypies/ abnormal behaviours were seen in the enriched cages and that may be explained by the possibility to manipulate and build nests. The long term effect, obtained from an open-field test, showed in the enriched mice higher locomotion level from zone2-zone3 and back. These results, interpreted as higher exploratory behaviours, are in concordance with Van Roy et al., (2001) who also scored higher frequencies of locomotion in an open field test with mice under enrichment conditions. However they observed fewer stretched attended postures (SAP) in their experiment and the mice in this study showed more SAP than the control animals. SAP is seen as risk assessment behaviour, described in Augustsson (2004) as “gaining information about a novel situation and a means to determine if an actual threat is present”. So these results can be seen as contradictive since the enriched housed mice showed more explorative and anxious related behaviours.

The time aspect of experiment 2 (period 1 and period 2) showed that feeding and rearing were performed more often the second period by both treatments. Van de Weerd et al., (1997) and Würbel et al., (1998) found that feeding decreased with age and that contradicts the results obtained in this study where the rats ate significantly more the second period.

Between the enriched housing system and the control cage a difference was observed in grooming and sleeping   where these behaviours was performed more by the control group. These two results contradict each other when grooming is said to show less in the animals with enrichment while sleeping is more prominent in an enriched system (Würbel et al., 1998). The fact that rearing occurred more in the control housing can easily is explained by the structure of the cage. In the control housing the roof was transparent and therefore inviting to rear, while in the enriched cage the roof was a maze through which the rats couldn’t see. During the open field test the control rats reared significantly more and walked more from zone 1 to zone 2 and back. The zone walking can indicate that they felt more comfortable and secure near the walls of the test. Rearing is seen as anxiety behaviour, the result from the test is quite passable but on the other hand there was no significant difference in the locomotion or explorative behaviours.  

When scientific research involves animal use, it should take into consideration their behaviours are factors that are products from the environment and genetics of the animal. Van de Weerd et al., 1997 has shown that enrichment, even though important for enhancing the animals’ welfare, did not alter scientific results or the physiology of the mice. Therefore no good reason seems to be found for depriving laboratory mice from nesting enrichment

The present study provide evidence that even simple enrichment may have great potential in reducing stereotypic behaviours, increase exploratory behaviour and may thus enhance the well-being in laboratory animals.


Augustsson, H., (2004) Ethoexperimental studies of behaviour in wild and laboratory mice. Veterinaria 174, Doctorial thesis, Swedish university of agricultural science, Uppsala.

Baumans, V., (2004) The welfare of laboratory mice.pp 119-152 in: Kaliste, E., The Welfare of Laboratory Animals. Kluwer Academic Publishers, The Netherlands 

Kaliste, E., Mering, S., (2004) The welfare of laboratory rats. pp 153-180 in: Kaliste, E., (2004) The Welfare of Laboratory Animals. Kluwer Academic Publishers, The Netherlands 

Olsson, I.A.S.,   Nevison, C.M., Pattersson-Kane E.G., Sherwin, C.M., Van de Weerd   H.A, Würbel.,   (2003)   Understanding behaviour: the relevance of ethological approaches in laboratory animal science. Applied Animal Behavioural science 81, 245-264

Roy, V., Belzung, C., Delarue, C., Chapillon, P., (2001) nvironmental enrichment in BALB/c mice. Effects in classical tests of anxiety and exposure to a predator odor. Physiology & Behaviour 74, 313-320

Sherwin, C.M & Glen, E.F (2003) Cage colour and effects of home cage colour on anxiety in laboratory mice. Animal Behaviour 66, 1085-1092

Van de Weerd, H.A., Van Loo, P.L.P., Van Zutphen L.F.M., Koolhaas, J.M., Baumans, V., (1997) Nesting materials as environmental enrichment has no adverse effects on behaviour and physiology og laboratory mice. Physiology & Behaviour 62(5): 1019-1028

Van der Harst, J.E., Fermont, P.C.J., Bilstra, A.E., Spruijt, B.M., (2003) Access to enriched housing is rewarding to rats as reflected by their anticipatory behaviour. Animal behaviour 66, 493-504

Würbel, H., Chapman, R., Rutland, C., (1998) Effects of feed and environmental enrichment on development of stereotypic wire-gnawing in laboratory mice. Applied animal behavioural science 60, 69-81

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Last updated: 05/19/05