Environmentally enriching American mink (Neovison vison) increases lymphoid organ weight and skeletal symmetry, and reveals differences between two sub-types of stereotypic behaviour

@deEnrichment studies for wild carnivores (e.g., in zoos) are often short-term, use enrichments of unknown motivational significance, and focus on glucocorticoids and stereotypic behaviour (SB), ignoring other stress-relevant variables. Our study assessed the broad behavioural and physiological effects of enriching American mink-a model carnivore-with preferred stimuli long-term, and investigated the welfare implications of individual differences in SB, We raised 64 male-female pairs with or without enrichment. At 7 months, pairs were split and mink individually housed (adults being solitary), first by being temporarily moved to identical non-enriched cages (permitting observation blind to rearing condition). Two weeks later, one mink per original pair (half female, half male) was returned to his/her rearing cage for re-observation, sample collection for faecal cortisol metabolite (FCM) analysis, and additional research for 1.5 years before being humanely killed. Stress-sensitive variables were then measured post-mortem. Enriched-raised mink in their rearing conditions excreted less FCM (F-1,F-29 = 833, p = 0.003), and performed less SB than non-enriched mink. Two SB sub-types occurred: (1) 'loco' stereotypies: locomotor, whole body and head stereotypies (e.g., pacing, nodding), previously shown to correlate with recurrent perseveration; and (2) repetitive scrabbling with the forepaws. Enriched housing reduced both (at 7 months: loco stereotypies: F-1,F-60 = 25.3, p < 0.0001; scrabbling: F-1,F-60 = 24.0, p < 0.001; effects still trends 1.5 years later). However, the sub-types responded differently to the current availability and/or usage of enrichment. Thus enrichment-use (which was stable) tended to negatively correlate with scrabbling but not loco stereotypies. Furthermore, after the relocation to identical non-enriched cages, loco stereotypies remained lower in enriched-reared than non-enriched-reared mink (F-1,F-58 = 31.33, p < 0.0001), but scrabbling rapidly increased (such that within two weeks, enriched- and non-enriched-reared mink were indistinguishable). Post-mortem, enriched-reared mink showed less skeletal fluctuating asymmetry (F-1,F-42 = 2.87, p = 0.048) and had heavier lymphoid organs (thymus: F-1,F-41 = 3.43, p = 0.035; spleen: F-1,F-45 = 13.11, p = 0.010). However, within treatment groups, neither these measures nor FCM covaried with SB. In conclusion, long-term housing with preferred enrichments not only reduced SB and FCM, but also induced anatomical changes consistent with better cell-mediated immunity and reduced developmental stress. In addition, these results should refine the use of SB and its sub-types in welfare assessment, since scrabbling seemed to reflect the prevailing presence/absence and utilisation of enrichment, while motor, whole body and head SBs appeared to reflect more stable, long-term effects of differential rearing; and furthermore, within each housing type, individual differences in SB appeared to reflect response styles rather than differential welfare. (C) 2016 Published by Elsevier B.V. @enEnrichment studies for wild carnivores (e.g., in zoos) are often short-term, use enrichments of unknown motivational significance, and focus on glucocorticoids and stereotypic behaviour (SB), ignoring other stress-relevant variables. Our study assessed the broad behavioural and physiological effects of enriching American mink-a model carnivore-with preferred stimuli long-term, and investigated the welfare implications of individual differences in SB, We raised 64 male-female pairs with or without enrichment. At 7 months, pairs were split and mink individually housed (adults being solitary), first by being temporarily moved to identical non-enriched cages (permitting observation blind to rearing condition). Two weeks later, one mink per original pair (half female, half male) was returned to his/her rearing cage for re-observation, sample collection for faecal cortisol metabolite (FCM) analysis, and additional research for 1.5 years before being humanely killed. Stress-sensitive variables were then measured post-mortem. Enriched-raised mink in their rearing conditions excreted less FCM (F-1,F-29 = 833, p = 0.003), and performed less SB than non-enriched mink. Two SB sub-types occurred: (1) 'loco' stereotypies: locomotor, whole body and head stereotypies (e.g., pacing, nodding), previously shown to correlate with recurrent perseveration; and (2) repetitive scrabbling with the forepaws. Enriched housing reduced both (at 7 months: loco stereotypies: F-1,F-60 = 25.3, p < 0.0001; scrabbling: F-1,F-60 = 24.0, p < 0.001; effects still trends 1.5 years later). However, the sub-types responded differently to the current availability and/or usage of enrichment. Thus enrichment-use (which was stable) tended to negatively correlate with scrabbling but not loco stereotypies. Furthermore, after the relocation to identical non-enriched cages, loco stereotypies remained lower in enriched-reared than non-enriched-reared mink (F-1,F-58 = 31.33, p < 0.0001), but scrabbling rapidly increased (such that within two weeks, enriched- and non-enriched-reared mink were indistinguishable). Post-mortem, enriched-reared mink showed less skeletal fluctuating asymmetry (F-1,F-42 = 2.87, p = 0.048) and had heavier lymphoid organs (thymus: F-1,F-41 = 3.43, p = 0.035; spleen: F-1,F-45 = 13.11, p = 0.010). However, within treatment groups, neither these measures nor FCM covaried with SB. In conclusion, long-term housing with preferred enrichments not only reduced SB and FCM, but also induced anatomical changes consistent with better cell-mediated immunity and reduced developmental stress. In addition, these results should refine the use of SB and its sub-types in welfare assessment, since scrabbling seemed to reflect the prevailing presence/absence and utilisation of enrichment, while motor, whole body and head SBs appeared to reflect more stable, long-term effects of differential rearing; and furthermore, within each housing type, individual differences in SB appeared to reflect response styles rather than differential welfare. (C) 2016 Published by Elsevier B.V.

Michigan State Univ
Univ Navarra
Veterinärmedizinische Universität Wien
University of Navarra
Michigan State University
University of Guelph