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Nest building and burrowing are highly motivated natural behaviors in rodents, and changes in these behaviors can serve as welfare assessment tools. In this study, we investigated: 1) the limits of agreement between 2 observers for a refined scoring method for nest-building behavior; 2) the effect of repeated exposure to 15 min of isoflurane on nest-building behavior; 3) the effect of 24 h of grid-floor housing, repeated exposure to 15 min isoflurane, and daily intraperitoneal injection of 0.2 mL 0.9% isotonic saline for 3 d on burrowing behavior; and 4) the effect of exposure to grid-floor housing, isoflurane, and intraperitoneal injections on fecal corticosterone metabolites, body weight, fur status, and sucrose preference in mice. SPF C57BL/6NTac female mice (n = 27) were included in the study and were assessed first for burrowing behavior, followed by 2 wk of rest and then for nesting behavior. The refined scoring method for nest-building activity had good inter observer agreement. According to this method, a single exposure to anesthesia with isoflurane led to a decrease in nest-building activity and sucrose preference; a second exposure to anesthesia with isoflurane had no effect on nest building. Neither grid-floor housing nor repeated exposure to isoflurane anesthesia had any effect on burrowing behavior in mice. In contrast, intraperitoneal injections increased burrowing behavior. In conclusion, a refined scoring method for nest-building activity test that we developed for this study proved to be objective and sensitive to the effect of an initial exposure to anesthesia with isoflurane.

It is argued that mice have poor colour vision and are insensitive to the colour red, which they in theory perceive as dark. Therefore, the red tinted Bio-Serv Mouse Igloo® is used to provide mice with a dark shelter while enabling humans to monitor the animals through the shelter without disturbing them. However, we do not know if mice like the colour red. Therefore, this study investigated whether mice prefer an amber or blue igloo over a red igloo, still making it possible for humans to see through the igloos. A preference test consisting of 3 cages each containing a different coloured igloo, connected to a barren central cage, was conducted for 11 h 20 min in 32 female B6 mice. The results showed that some female B6 mice did not like to use the Bio-Serv Mouse Igloo® as a shelter, regardless of colour. Almost half of the mice chose to stay outside the igloos, but when choosing an igloo the mice preferred the blue or amber igloo over the red igloo.

Environmental enrichment is increasingly being used to enhance welfare among laboratory animals, as environmental surroundings such as housing conditions have a great impact on the animals. However, when introducing environmental enrichment it is important to investigate whether a negative effect on behavior and physiological parameters and thus on the welfare of the animals occur. This study is a randomized trial investigating the effect of supplementing standard housing with a hemp rope or a cardboard pipe, as part of environmental enrichment, on agonistic and social behavior, stress and anxiety level in male C57bl/6 mice. Moreover, it was investigated whether a possible increase in agonistic behavior was correlated with high levels of testosterone. The social interaction test measured agonistic and social behavior, number of wounded companion animals was used as a surrogate measure of agonistic behavior, fecal corticosterone levels measured stress, the elevated plus maze measured anxiety and testosterone was measured in serum. Three hundred thirty six male C57bl/6 mice were randomized to (1) standard environment, (2) supplement of a hemp rope or (3) supplement of a cardboard pipe. We found no agonistic behavior in any of the three groups, but a significantly higher number of wounded companion animals among the hemp rope and the cardboard pipe groups. Both intervention groups showed more social behavior and produced more corticosterone. No difference was detected in anxiety and testosterone levels between the three groups. Future studies are needed to investigate the effect on welfare in more depth.