Table 1.

Questions and issues relevant to the use of environmental enrichment in rodents

	Question	Issues
1	What is enrichment?	Definitions of EE vary widely. Reliance on professional judgment in the context of experimental goals is crucial to the development of sound approaches to providing EE. Variation across rodent species and strains, together with the wide range of experimental goals, complicates the development of highly inclusive, prescriptive, or preemptive statements about EE.
2	What is enrichment intended to accomplish?	The goals of EE should be carefully defined, with measurable outcomes that benefit the animal in a significant way in terms of stimulation of positive species-typical behaviors and/or prevention of abnormal or undesirable behaviors.
3	How is an enriched environment related to standardized housing and a natural habitat?	Some components of the standard rodent environment might be considered to provide EE (for example, bedding, grilled cage tops, group housing, behavioral training), particularly for rodents maintained for a relatively short period of time.
4	Who should determine whether a given enrichment intervention benefits and/or does not harm the animal or the science?	EE should not be imposed unilaterally or arbitrarily by any of the stakeholders. Prior consideration of potential impact on research outcomes is essential. Evidence should be available to document that specific forms of EE will not confound experimental outcomes and/or will alleviate harm that occurs in the absence of the EE. A corollary of this point is that funding is typically not available to support studies of the impact of EE on the animals or the research.
5	What is ‘enough’ enrichment, and how can that be measured?	Common indices of animal wellbeing are variables such as food intake, growth, and appropriate breeding performance, which are commonly satisfactory under standard rodent housing conditions. Determining the amount or form of EE needed to produce a positive impact without causing harm is a complex task.
6	What are the potential negative consequences of EE?	In some situations, EE interventions may cause overt harm to animals, influence statistical considerations, confound interpretation of the data, or impede the replication of findings across laboratories.
7	What are potential negative consequences of social housing?	Social animals can be highly territorial and/or develop hierarchical relationships that may adversely affect both high- and low-ranking animals. The presence of both dominant and submissive individuals also creates variability among animals in the group.