A targeted approach to developing environmental enrichment for two strains of laboratory mice

Structural enrichment for laboratory mice: exploring the effects of novelty and complexity

Providing structural enrichment is a widespread refinement method for laboratory rodents and other animals in captivity. So far, animal welfare research has mostly focused on the effect of increased complexity either by accumulating or combining different enrichment items. However, increasing complexity is not the only possibility to refine housing conditions. Another refinement option is to increase novelty by regularly exchanging known enrichment items with new ones. In the present study, we used pair-housed non-breeding female C57BL/6J and DBA/2N mice to investigate the effect of novelty when applying structural enrichment. We used a double cage system, in which one cage served as home cage and the other as extra cage. While the home cage was furnished in the same way for all mice, in the extra cage we either provided only space with no additional enrichment items (space), a fixed set of enrichment items (complexity), or a changing set of enrichment items (novelty). Over 5  weeks, we assessed spontaneous behaviors, body weight, and extra cage usage as indicators of welfare and preference. Our main results showed that mice with access to structurally enriched extra cages (complexity and novelty) spent more time in their extra cages and complexity mice had lower latencies to enter their extra cages than mice with access to the extra cages without any structural enrichment (space). This indicates that the mice preferred the structurally enriched extra cages over the structurally non-enriched space cages. We found only one statistically significant difference between the novelty and complexity condition: during week 3, novelty mice spent more time in their extra cages than complexity mice. Although we did not detect any other significant differences between the novelty and complexity condition in the present study, more research is required to further explore the potential benefits of novelty beyond complexity.

Environmental Complexity and Research Outcomes

Environmental complexity is an experimental paradigm as well as a potential part of animals' everyday housing experiences. In experimental uses, researchers add complexity to stimulate brain development, delay degenerative brain changes, elicit more naturalistic behaviors, and test learning and memory. Complexity can exacerbate or mitigate behavioral problems, give animals a sense of control, and allow for expression of highly driven, species-typical behaviors that can improve animal welfare. Complex environments should be designed thoughtfully with the animal's natural behaviors in mind, reported faithfully in the literature, and evaluated carefully for unexpected effects.

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

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.

To Group or Not to Group? Good Practice for Housing Male Laboratory Mice

Simple Summary

Wild mice live in territories inhabited by one adult male, several females, and their offspring. This cannot be replicated in the laboratory, so male mice are usually housed in single-sex groups or individually. However, there can be serious animal welfare problems associated with both these approaches, such as lack of social contact when housed individually or aggression between males when kept in groups. Group housing is widely recommended to give male laboratory mice the opportunity to behave as ‘social animals’, but social stress can be detrimental to the welfare of these animals, even without injurious fighting. All of this can also affect the quality of the science, giving rise to ethical concerns. This review discusses whether it is in the best welfare interests of male mice to be housed in groups, or alone. We conclude that it is not possible to give general recommendations for good practice for housing male laboratory mice, as responses to single- and group-housing can be highly context-dependent. The welfare implications of housing protocols should be researched and considered in each case.

Abstract

It is widely recommended to group-house male laboratory mice because they are ‘social animals’, but male mice do not naturally share territories and aggression can be a serious welfare problem. Even without aggression, not all animals within a group will be in a state of positive welfare. Rather, many male mice may be negatively affected by the stress of repeated social defeat and subordination, raising concerns about welfare and also research validity. However, individual housing may not be an appropriate solution, given the welfare implications associated with no social contact. An essential question is whether it is in the best welfare interests of male mice to be group- or singly housed. This review explores the likely impacts—positive and negative—of both housing conditions, presents results of a survey of current practice and awareness of mouse behavior, and includes recommendations for good practice and future research. We conclude that whether group- or single-housing is better (or less worse) in any situation is highly context-dependent according to several factors including strain, age, social position, life experiences, and housing and husbandry protocols. It is important to recognise this and evaluate what is preferable from animal welfare and ethical perspectives in each case.

The effect of early life experience, environment, and genetic factors on spontaneous home-cage aggression-related wounding in male C57BL/6 mice

Aggression is a major welfare issue in mice, particularly when mice unfamiliar to each other are first placed in cages, as happens on receipt from a vendor, and following cage cleaning. Injuries from aggression are the second leading cause of unplanned euthanasia in mice, following ulcerative dermatitis. Commonly employed strategies for reducing aggression-related injury are largely anecdotal, and may even be counterproductive. Here we report a series of experiments testing potential explanations and interventions for post-shipping aggression-related injuries in C57BL/6 mice. First, we examined the effects of weaning: testing whether manipulating weaning age reduced aggression-related injuries, and if repeated mixing of weaned mice before shipping increased these injuries. Contrary to our predictions, repeated mixing did not increase post-shipping injurious aggression, and early weaning reduced aggression-related injuries. Second, we examined potential post-shipping interventions: testing whether lavender essential oil applied to the cage reduced aggression-related injuries, and whether a variety of enrichments decreased injurious aggression. Again, contrary to predictions, lavender increased wounding, and none of the enrichments reduced it. However, consistent with the effects of weaning age in the first experiment, cages with higher mean body weight showed elevated levels of aggression-related wounding. Finally, we tested whether C57BL/6 substrains and identification methods affected levels of intra-cage wounding from aggression. We found no effect of strain, but cages where mice were ear-notched for identification showed higher levels of wounding than cages where mice were tail-tattooed. Overall, these results emphasize the multifactorial nature of home-cage injurious aggression, and the importance of testing received wisdom when it comes to managing complex behavioral and welfare problems. In terms of practical recommendations to reduce aggressive wounding in the home cage, tail tattooing is recommended over ear notching and late weaning should be avoided.

Assessing the welfare of laboratory mice in their home environment using animal-based measures--a benchmarking tool

Welfare problems in laboratory mice can be a consequence of an ongoing experiment, or a characteristic of a particular genetic line, but in some cases, such as breeding animals, they are most likely to be a result of the design and management of the home cage. Assessment of the home cage environment is commonly performed using resource-based measures, like access to nesting material. However, animal-based measures (related to the health status and behaviour of the animals) can be used to assess the current welfare of animals regardless of the inputs applied (i.e. the resources or management). The aim of this study was to design a protocol for assessing the welfare of laboratory mice using only animal-based measures. The protocol, to be used as a benchmarking tool, assesses mouse welfare in the home cage and does not contain parameters related to experimental situations. It is based on parameters corresponding to the 12 welfare criteria established by the Welfare Quality® project. Selection of animal-based measures was performed by scanning existing published, web-based and informal protocols, and by choosing parameters that matched these criteria, were feasible in practice and, if possible, were already validated indicators of mouse welfare. The parameters should identify possible animal welfare problems and enable assessment directly in an animal room during cage cleaning procedures, without the need for extra equipment. Thermal comfort behaviours and positive emotional states are areas where more research is needed to find valid, reliable and feasible animal-based measures.

Reducing mouse anxiety during handling: effect of experience with handling tunnels

Handling stress is a well-recognised source of variation in animal studies that can also compromise the welfare of research animals. To reduce background variation and maximise welfare, methods that minimise handling stress should be developed and used wherever possible. Recent evidence has shown that handling mice by a familiar tunnel that is present in their home cage can minimise anxiety compared with standard tail handling. As yet, it is unclear whether a tunnel is required in each home cage to improve response to handling. We investigated the influence of prior experience with home tunnels among two common strains of laboratory mice: ICR(CD-1) and C57BL/6. We compared willingness to approach the handler and anxiety in an elevated plus maze test among mice picked up by the tail, by a home cage tunnel or by an external tunnel shared between cages. Willingness to interact with the handler was much greater for mice handled by a tunnel, even when this was unfamiliar, compared to mice picked up by the tail. Once habituated to handling, C57BL/6 mice were most interactive towards a familiar home tunnel, whereas the ICR strain showed strong interaction with all tunnel handling regardless of any experience of a home cage tunnel. Mice handled by a home cage or external tunnel showed less anxiety in an elevated plus maze than those picked up by the tail. This study shows that using a tunnel for routine handling reduces anxiety among mice compared to tail handling regardless of prior familiarity with tunnels. However, as home cage tunnels can further improve response to handling in some mice, we recommend that mice are handled with a tunnel provided in their home cage where possible as a simple practical method to minimise handling stress.

Conservation by design

Conservation researchers are increasingly aware of the need to conduct interdisciplinary research and to engage nonscientists in practical applications of conservation biology. But so far, industrial designers have been left out of such collaboration and outreach efforts. Conservation of wildlife often depends on products such as nest boxes, feeders, barriers, and corridors, all of which have a designed component that is frequently overlooked. Furthermore, many products are adopted without testing on short or long time scales. We argue that the design of products for conservation, and hence their functionality, effectiveness, and value, can be improved through collaboration with industrial designers. We see four key benefits that can arise from interactions with industrial designers: improvement of product quality and value, innovation and improvement in functionality of products, harmonization of conservation products with local values, and development of a psychological biomimesis approach to design. The role of industrial designers in conservation projects would be to improve factors such as product durability, affordability, functionality, and aesthetic appeal to local people. Designers can also help to create multiple product options whose success can be tested in the field. We propose that collaborations with industrial designers can contribute to the development of improvements to existing products and innovations in the practice of animal conservation.