The assessment of bar chewing as an escape behaviour in laboratory mice
The ability to measure objectively how an animal perceives its home environment is essential for improving the housing and husbandry conditions of laboratory animals. Chewing at cage bars by a rodent may reflect the animal's desire to escape from its home cage and thus provide a measure
of the relative aversiveness or inadequacy of different housing conditions from the animal's viewpoint. To assess whether bar chewing by laboratory mice is an escape behaviour, adult male and female ICR-(CD-1) mice were housed individually or in same-sex groups of three in modified shoebox-type
cages. Cages had two sets of external bars in the side walls, an equivalent set of bars fixed internally and a Perspex lid. One set of external bars opened daily, allowing the mice to escape into a larger arena. All mice showed a strong preference for chewing at external bars over those that
were internal to each cage. After one week of experience, mice also preferred the external bars that opened daily to those that did not open. Behaviour directed towards the cage lid declined over time as the mice experienced the new escape route in the cage side. Interest in the external bars
correlated positively with time since last escape. Results confirm that bar chewing reflects an attempt to escape the cage and explore the surrounding area and may provide a suitable behavioural measure of perception of the cage environment for use in welfare assessment.