Effects of Cage Enrichment on Behavior, Welfare and Outcome Variability in Female Mice

Abstract

The manner in which laboratory rodents are housed is driven by economics (minimal use of space and resources), ergonomics (ease of handling and visibility of animals), hygiene, and standardization (reduction of variation). This has resulted in housing conditions that lack sensory and motor stimulation and restrict the expression of species-typical behavior. In mice, such housing conditions have been associated with indicators of impaired welfare, including abnormal repetitive behavior (stereotypies, compulsive behavior), enhanced anxiety and stress reactivity, and thermal stress. However, due to concerns that more complex environmental conditions might increase variation in experimental results, there has been considerable resistance to the implementation of environmental enrichment beyond the provision of nesting material. Here, using 96 C57BL/6 and SWISS female mice, respectively, we systematically varied environmental enrichment across four levels spanning the range of common enrichment strategies: (1) bedding alone; (2) bedding + nesting material; (3) deeper bedding + nesting material + shelter + increased vertical space; and (4) semi-naturalistic conditions, including weekly changes of enrichment items. We studied how these different forms of environmental enrichment affected measures of animal welfare, including home-cage behavior (time–budget and stereotypic behavior), anxiety (open field behavior, elevated plus-maze behavior), growth (food and water intake, body mass), stress physiology (glucocorticoid metabolites in fecal boluses and adrenal mass), brain function (recurrent perseveration in a two-choice guessing task) and emotional valence (judgment bias). Our results highlight the difficulty in making general recommendations across common strains of mice and for selecting enrichment strategies within specific strains. Overall, the greatest benefit was observed in animals housed with the greatest degree of enrichment. Thus, in the super-enriched housing condition, stereotypic behavior, behavioral measures of anxiety, growth and stress physiology varied in a manner consistent with improved animal welfare compared to the other housing conditions with less enrichment. Similar to other studies, we found no evidence, in the measures assessed here, that environmental enrichment increased variation in experimental results.

Effects of different social experiences on emotional state in mice

“…Thus, in summary, we did not detect clear effects of the different social experiences on the animals' cognitive judgement bias in the present study. www.nature.com/scientificreports/ While equivocal findings are not an exception in the field of cognitive bias research in mice 26,29 , the present results still deviate from our expectations based on previous studies, reporting effects of the same experiences as provided here on the emotional state of mice 30,31,41 . Interestingly, however, we also did not detect effects of the social experiences on anxiety-like behaviour, exploratory locomotion and corticosterone metabolite levels.…”

“…Thus, the modulation of judgement biases in mice is far from being understood. Moreover, the focus has been put on the investigation of negative affective states, while effects of putatively positive experiences remain understudied (but see also 29 ).…”

Pair housing makes calves more optimistic

“…The direction of the treatment differences was consistent across all three ambiguous cues (i.e. PAIR calves showed more Go responses in NN, M and NP trials), indicating that our treatment effect is relatively robust compared to other studies, where animals from one treatment sometimes show a positive bias in one but a negative bias in another ambiguous trial type, rendering the findings hard to interpret 47,48 .…”

Neonatal Hypoxic-Ischemic Encephalopathy Yields Permanent Deficits in Learning Acquisition: A Preclinical Touchscreen Assessment

“…This variability can be beneficial, as it mimics the variation of injury observed in infants following HIE. Additionally, no environmental enrichment was used in the study, which could impact the neurodevelopmental outcomes (61,62). Both sexes were utilized in this study, which adds to the generalizability of the results.…”