Environmental Complexity and Research Outcomes

Abstract

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.

Environmental Enrichment for Rats and Mice Housed in Laboratories: A Metareview

“…Baumans and Van Loo [ 69 ] (p. 26) used the term “environmental refinement” to indicate the ongoing process of providing more than just the basic needs of animals, highlighting that the term “enrichment” is sometimes taken to imply that animals are provided with luxuries. Pritchett-Corning [ 74 ] (p. 239) used the descriptive (rather than evaluative) term “environmental complexity”, explaining that this ranges from barren to naturalistic conditions, and that varying categories of environmental enrichment (standard, superenriched, and semi-naturalistic) exist within this range. Sørensen et al [ 61 ] used the terms enrichment and complexity interchangeably.…”

“…Sørensen et al [ 61 ] used the terms enrichment and complexity interchangeably. Würbel and Garner [ 54 ] (p. 3) differentiated between possible enrichment outcomes, using the term “beneficial enrichment” for enrichment that is biologically relevant and improves animal welfare, and referring to enrichment attempts that are not biologically relevant or potentially harmful as “pseudoenrichment.” “Superenrichment” was defined separately from environmental enrichment in two articles, without consensus [ 64 , 74 ]. Our own view is that despite the shortcomings of the term, “environmental enrichment” is so engrained in the literature that it is unlikely that any alternative will soon replace it.…”

“…Some earlier authors were sceptical regarding implementation of enrichment, promoting a more cautious approach to even basic cage modifications (e.g., [ 7 , 56 , 63 ]); however, more supportive views also existed in earlier years (e.g., [ 13 , 55 , 57 ]), so it is unclear if perceptions have changed consistently over time. That said, more recent publications generally support the provision of more extensive environmental enrichment for laboratory rodents [ 46 , 73 , 74 ]; some more basic recommendations, like solid cage floors [ 55 , 57 ], were present only in earlier reviews (likely because wire flooring is no longer common). Three articles made no overall recommendations due to the lack of consensus or the perceived need for more research.…”

“…Negative effects on animal health, behaviour, and wellbeing were identified as risks of enrichment in several articles. Some of these articles identified how poor choices of enrichment materials could increase injury or disease [ 7 , 72 , 74 ]. For example, paper tissues have been identified as inappropriate enrichment for mice used in asthma studies, because the cellulose fibres of these tissues contribute to inflammatory reactions of the lungs [ 137 ].…”

The use of ball pits and playpens in laboratory Lister Hooded male rats induces ultrasonic vocalisations indicating a more positive affective state and can reduce the welfare impacts of aversive procedures

“…Animals living in an enriched environment with lower stress levels and improved well-being should provide a better model for research, and are likely to generate more reliable and reproducible data with less variability. 11,26…”