The welfare of fur-farmed mink. Captive animals may suffer if strongly motivated to perform activities that their housing does not allow. We investigated this experimentally for caged mink, and found that they would pay high costs to perform a range of natural behaviours, and release cortisol if their most preferred activity, swimming, was prevented. Mink on fur farms may thus suffer from frustration. Fur farming is widespread in North America, Scandinavia and Europe, approximately 30 million mink pelts being produced annually worldwide. On farms, American mink (Mustela vison) are kept in wire mesh cages c. 0.9 x 0.4 x 0.3 m containing a single nest-box, and access to drinking-water and a paste-like food. Those opposed to fur farming claim that this causes frustration , as in the wild, mink would patrol territories 1-4 km long, use several nest-sites, and hunt by following scent trails, investigating burrows, and diving and swimming for aquatic prey . Others, however, argue that farmed minks' excellent health and breeding success show adaptation to captivity . We addressed this issue objectively by measuring the costs paid by farm-raised mink to acquire resources enabling natural behaviours. Because of the key role of pleasure in motivating choice behaviour this approach pinpoints activities important for welfare. Eight male and eight female adult mink were individually housed in closed economy set-ups, each consisting of a conventional farm cage, plus seven similarly-sized resource compartments. These contained: 1) access to a waterpool beneath the cage, c. 1.5m x 0.5m, filled with 0.2m water; 2) a raised platform reached by a 2m vertical wire tunnel; 3) novel objects (e.g. discarded packaging, traffic cones, etc., changed daily); 4) an alternative nest-site (a wire box of hay); 5) toys for manipulation and chewing (e.g. tennis balls); and 6) a plastic tunnel; the seventh was left empty, to control for the importance of accessing additional space. Access costs were imposed by weighting one-way entrance-doors by 0kg, 0.25kg, 0.5kg, 0.75kg, 1kg or 1.25kg for seven successive days. Compartment-use was automatically recorded 24h/day, allowing calculation of four measures of value. The results are given in Table 1. Using seven males and seven females, we then blocked access to each of four resources for 24 hours to record endocrine stress responses . These were behavioural resources of high, intermediate, and low value (the water-pool, alternative nest-site and empty compartment respectively), and an essential physiological resource: food. During each treatment, urine was collected for the assay of excreted cortisol; creatinin was also assayed to enable correction for differences in urinary concentration. When deprived of food, urinary cortisol increased by 50.0±16.1% over baseline levels (Paired t = 2.77, df = 13, p < 0.05); it also increased, by 33.8±11.2%, when access to the water-pool was blocked (t = 2.75, p < 0.05). These two effects did not significantly differ (t = 2.47, p > 0.05). Cortisol excretion did not...
