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

Abstract

Effects of sub-optimal housing on inactivity vary across species and experiments, probably because inactivity is heterogeneous, reflecting both positive states (e.g. relaxation) and negative ones (e.g. fear). We therefore aimed to identify specific subtypes of inactivity that could indicate poor welfare in mink, by comparing their behaviour in enriched and non-enriched conditions (the former having been previously demonstrated to be highly preferred by mink and to enhance their welfare). We assessed this in three groups of subjects, as well as after housing conditions were reversed for the last group. During live scans, inactive animals were scored for posture, location, and whether awake or apparently asleep. Data on temperament and physiological stress indicators were also collected for one group; these confirmed that non-enriched housing increased faecal cortisol metabolites (FCM; P=0.040). Non-enriched housing also increased locomotor stereotypy in females (sex*housing: P=0.004). Inactivity in the nest-box (vs. in the open cage) was higher among females in non-enriched housing (housing*sex P<0.001), and increased by 20% of observations after enrichment removal (P=0.018) for both sexes. Furthermore, males with fearful temperaments spent the most time inactive in the nest-box (sex*temperament P=0.054), while females whose FCM decreased most when given enrichment also showed the largest decreases in this behaviour (sex*FCM change P=0.019). Together, this suggests that inactivity in the nest-box may reflect anxiety-induced hiding. Lying awake (i.e. prone with eyes open) was also higher in non-enriched housing (3.1% of observations vs. 1.7%; P=0.002); furthermore, this subtype of inactivity increased after enrichment removal (by 1.0% of observations; P=0.021), and decreased when non-enriched mink were given enrichment (by 2.4% of observations; P=0.004). This behaviour did not co-vary with fearfulness, however, nor with FCM (both P>0.05). This suggests that lying awake is not fear-related (e.g. not reflecting enhanced vigilance) but instead reflects some other negative state. Effects on inactivity subtypes as defined by posture were less consistent. For example, time spent lying belly down tended to decrease in mink moved from non-enriched to enriched cages (P=0.054), but enriched mink spent significantly less time belly down (in one of the three groups; P=0.002). Overall, two subtypes of inactivity, lying in the nestbox and lying awake seem likely to be valid indicators of housing-induced poor welfare in this species, being consistently increased by non-enriched cages. Lying in the nest-box may indicate fear or anxiety, and lying awake, a boredom-like state.

Benefits of a Ball and Chain: Simple Environmental Enrichments Improve Welfare and Reproductive Success in Farmed American Mink (Neovison vison)

“…Power tests suggested that a minimum of approximately 30 mink per group were needed to detect a housing effect of equal size to that found in a previous study [59]. Faecal samples were collected from at least that number of mink per farm and treatment, resulting in a total sample of 188 females across all farms, representing all sister pairs housed in the same randomly chosen area of one shed per farm.…”

Age‐dependent baseline values of faecal cortisol metabolites in the American mink (Neovison vison) under semi‐natural housing conditions

“…Meagher et al. () came to the same result that minks with no access to a second cage had higher FCM levels than minks with access to it.…”

“…Hansen et al., ; Svendsen et al., ; Meagher et al., ) mostly deals with female mink, which is why there is only few data on male mink (e.g. Meagher et al., ). The trial groups tested in our study contained both male and female animals.…”

Feed intake, growth, and behavioral assessment of mink fed a clam-based diet

“…Following the positioning change in the shed, the observational sampling increased to six days with three sets of 3 min focal observations each day to ensure adequate sampling of activity due to high levels of resting being observed (see Results). These observations were made standing as far back from the focal cages as possible (distance 1 m), a technique previously used successfully (Meagher et al 2013). The behaviors recorded were "activity" (walking, sniffing, eating, drinking, grooming etc.…”

“…The behaviors recorded were "activity" (walking, sniffing, eating, drinking, grooming etc. ), "resting" (lying still with eyes open or closed), "scrabbling" (scratching at a surface with front paws), and "locomotor stereotypy" (three or more replicates of pacing, bobbing, circling, routetracing; Meagher et al 2013). All observations took place in the morning after sunrise and prior to feeding.…”