Environmental standardization: cure or cause of poor reproducibility in animal experiments?

Abstract

It is widely believed that environmental standardization is the best way to guarantee reproducible results in animal experiments. However, mounting evidence indicates that even subtle differences in laboratory or test conditions can lead to conflicting test outcomes. Because experimental treatments may interact with environmental conditions, experiments conducted under highly standardized conditions may reveal local 'truths' with little external validity. We review this hypothesis here and present a proof of principle based on data from a multilaboratory study on behavioral differences between inbred mouse strains. Our findings suggest that environmental standardization is a cause of, rather than a cure for, poor reproducibility of experimental outcomes. Environmental standardization can contribute to spurious and conflicting findings in the literature and unnecessary animal use. This conclusion calls for research into practicable and effective ways of systematic environmental heterogenization to attenuate these scientific, economic and ethical costs.

Association between exploratory activity and social individuality in genetically identical mice living in the same enriched environment

“…Stereotypic behavior is assumed to result from an intrinsic urge to carry out certain innate behaviors serving specific and essential purposes in the wild animal that in a cage cannot be appropriately performed due to spatial constraints and lack of appropriate environmental conditions. In captive animals, stereotypic behaviors are usually considered a sign of stress and often accompanied by social or cognitive deficits (Richter et al, 2009;Gross et al, 2012). Even though the CTR animals had patches of fur missing, probably due to over-grooming, none of the large enclosure inhabitants showed anything of this sort, nor were they observed to carry out behaviors classifiable as stereotypical.…”

The effects of enrichment novelty versus complexity in cages of group-housed rats (Rattus norvegicus)

“…It has also been shown that they can be beneficial for welfare without increasing variation in data and, at the same time, may increase the external validity of studies (Richter et al 2009;Würbel and Garner, 2007;Würbel, 2007). Therefore, enrichment may not only improve the welfare of laboratory rodents, but also the overall validity of research, hence resulting in a reduction in the number of animals used.…”

Laboratory environmental factors and pain behavior: the relevance of unknown unknowns to reproducibility and translation

“…In one of our studies, a particularly robust strain difference in pain sensitivity 127 was found eventually to exist only because of SIA-resulting simply from being placed in the testing room itself-in one strain but not the other; if mice were habituated to the room on several days before testing no strain difference was observed 36 . These sorts of findings have led to a discussion as to whether reproducibility in animal experiments would be enhanced by standardization of husbandry and experimental parameters across laboratories 128 . Some have argued for such standardization in the name of sample size reduction, and improving comparability of results within and between laboratories 129 .…”

“…In fact, some have argued that attempts over the last few decades to standardize between laboratories in the name of reproducibility have actually led to a "standardization fallacy", producing results that are increasingly distinct between laboratories (and thus, perversely, less reproducible) 132 . A proposed solution to the problem is systematic variation of experimental conditions 128,133 , although I see a real danger here in presupposing which environmental factors actually matter.…”