Individual differences in stereotypic behaviour predict individual differences in the nature and degree of enrichment use in caged American mink

Abstract

a b s t r a c tEnvironmental enrichment (EE) reduces stereotypic behaviour (SB), but typically only partially. Using American mink (n = 17) as models, we tested the hypotheses that the effectiveness of EE reflects the degree to which subjects utilise it, and also the SB's degree of 'establishment' (its frequency and within-bout predictability). In Non-Enriched cages, our subjects performed Carnivora-typical Locomotor SBs; some also stereotypically scrabbled against the cage walls. Each mink was then enriched: re-housed in a cage connected by an overhead tunnel to a compartment enriched with manipulable objects and running water. Here, both types of SB declined (Locomotor SB: from 5.8% to 0.9% of observations; Scrabbling: from 1.6% to 0.2%). Individual differences in these lowered SB levels were stable, correlating positively between observation periods ( ≥ +0.66). Similar stability was evident in all measures of enrichment use (partial r ≥ + 0.74). However, predictions that EE would be least effective for 'established', i.e. highly frequent or predictable, SBs were not supported. Furthermore, nor did low enrichment use predict small reductions in SB: instead, unexpectedly, frequent interactions with enrichment items predicted the smallest absolute reductions in Locomotor SB (partial r = + 0.55). This was because the smallest reductions in this SB occurred in mink with the lowest pre-enrichment levels (partial r = −0.60), who also interacted most with the enrichments (partial r = −0.52). Mink with high pre-enrichment levels of Locomotor SB, in contrast, rarely interacted with the enrichments, instead becoming more inactive (partial r = + 0.52). These individuals were also perseverative (displaying more inappropriate response repetition in a previous food-rewarded guessing task), thence potentially behaviourally inflexible. However, their perseveration did not predict less interaction with enrichments. Furthermore, these animals did markedly alter their behaviour when enriched, reducing their SB and shifting their preferred resting locations from home cages to the overhead tunnels (partial r = + 0.70): individual differences that were, again, stable over time (co-variance across observation periods for inactivity in different areas: partial r ≥ +0.65). Individuals thus used enriched environments in consistent, qualitatively different ways that were predicted by pre-enrichment levels of Locomotor SB: low-SB mink became more active when enriched, frequently engaging with manipulable objects and running water, while high-SB subjects instead shifted resting locations and became more inactive. These divergent response styles are unexpected: not predicted by any current understanding of SB. The underlying mechanisms and generality to other species therefore now need investigation.

Sleeping tight or hiding in fright? The welfare implications of different subtypes of inactivity in mink

“…Hansen et al, 2007;Mason et al, 2001) as motivating and stress-reducing for mink. Previous studies from our laboratory confirmed that these cages benefit mink: subjects would push heavily weighted doors to access them (Dallaire et al, 2012), and they reduced stereotypic behaviour, faecal glucocorticoid metabolites, and several other signs of stress in animals raised in them (Díez-León and Mason, 2010;Campbell et al, 2013). Our first set of hypotheses was that non-enriched cages would: 1a) reduce time spent sleeping rather than lying awake; 1b) increase time spent inactive in the nest-box, and decrease inactive time in exposed areas of the cage; and 1c) influence the postures shown while inactive.…”

“…NE cages were 75 (L) x 60 (W) x 45 (H) cm, with a nest-box on the front. E cages consisted of an identical home cage, plus access to a second cage 120 cm wide via an overhead "tunnel" built of wire mesh (see diagram in Dallaire et al 2012). This second cage included a trough of running water to allow wading and head-dipping, a plastic "hammock", and many manipulable objects, new ones added monthly.…”

Effects of environmental enrichment and stereotypic behavior on maternal behavior and infant viability in a model carnivore, the American mink (Neovison vison)

“…This was double the size of the home cage, and contained an extra nestbox, a swing, circulating water in which to wade, and several manipulable objects, some familiar, some new each month (Díez‐León et al, ; Díez‐León, ). These enrichments were known to be highly preferred by mink (Dallaire et al, ), and the whole enriched environment was known to be effective at reducing stereotypic behavior, physiological stress, and perseveration (Mason et al, ; Hansen et al, ; Campbell et al, ; Díez‐León et al, ); our females were born and raised in these environments. E females were successfully encouraged to whelp in the home cage's nest box by never providing nesting material in the enriched compartment's nest box.…”

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

“…Replacing enrichment items every week has similarities with housing rats in cages containing different enrichment items which has been shown to produce different responses and to vary in its effects on welfare (Abou-Ismail, 2011;Dallaire et al, 2012;Campbell et al, 2013;Sharp et al, 2014).…”