Axelsson, H. M. K., Hansen, S. W., Loberg, J. et al. 2017. Effects of group size on behaviour, growth and occurrence of bite marks in farmed mink. Applied Animal Behaviour Science 194, 112-119.

The aims of this study were to investigate the occurrence of stereotypic behaviours and the activity level in farmed mink when group housed in climbing cages and if group housing increase aggression by assessing the prevalence of bite marks. This was studied in juvenile mink of the colour types “demibuff” (n=165) and “half sapphire” (n=165). The animals were housed in standard cages (S2: one male, one female), or in climbing cages (C2: one male, one female; C3: one male, two females; C4: two males, two females). Behaviours were recorded for two hours beginning at sunrise and two hours before sunset during six periods of five days each from August-October. After pelting, the leather side of the undried skins were visually inspected for bite marks. Stereotypic behaviours were infrequent (0.1% of observations). Pair housed mink in climbing cages were more “inactive out in cage” than pair housed mink in standard cages (p<0.0001), but cage type had no effect on the behaviours “being in nest box”, “active out in cage”, “interactions with enrichments” or “social interactions” (n.s.). Group sizes of three or four mink increased the behaviours “active out in cage” (P<0.0001) and decreased “being in nest box” (P<0.001) but had no effect on “interactions with enrichments”, “inactive out in cage” or “social interactions” (n.s.). Males had lower growth when kept in groups of four compared to groups of three or pairs (P<0.001), and shorter skin lengths when kept in groups of four compared to pairs (P<0.001), but females did not differ in growth or skin lengths between group sizes (n.s.). Number of bite marks on the leather side of the skins did not differ between cage types (n.s.) or group sizes (n.s.). In conclusion, neither the cage design nor the group size affected the occurrence of stereotypies or the occurrence of bite marks, but activity levels increased and the use of a nest box and male growth decreased in larger groups.

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