tFor many years, bite marks have been used as an indicator for aggression in mink productionsystems. However, the validity of bite marks as indicator of aggression has recently beenquestioned. We therefore tested the following hypotheses: (1) experimentally applied pressure to, or penetration of, the pelt during the growth phase of the winter coat will producemarks that can be recognized as bite marks at pelting, (2) bite marks applied experimentally by use of an artificial tooth or occurring due to social/aggressive interactions (bites)between mink are only visible if pressure/bite on the mink skin is applied during the activegrowth phase of the winter coat prior to time when matured, (3) bite marks will be easierto detect on dark mink than on mink with light coloured fur and (4) the number of bitemarks accumulates and increases with time mink are housed in groups. The experimentalmink were of the brown colour type (N = 140) and the white colour type (N = 60). Twentybrown and 20 white mink (housed in pairs since weaning) were housed individually at theage of 16 weeks. Every second week (at the age of 20, 22, 24, 25 and 28 weeks), four brownand four white mink were subjected to pressure by an artificial tooth. Before pressure wasapplied, each mink was anaesthetized and pain treated.In order to investigate when bite marks from cage mates are inflicted and to what extendthey accumulate over time, 120 brown and 40 white juvenile mink were placed in groupsof four in climbing cages after weaning. Every second week (at the age of 20, 22, 24, 26 and28 weeks) group housed mink were moved to single housing in standard cages in order toprevent further bites from cage mates.At the age of 29 weeks, all mink were killed individually by CO2and the pelts wereexamined for bite marks.The results showed that: (1) experimentally applied pressure on the skin can be recog-nized as bite marks in brown mink at pelting, (2) bite marks are easier to detect on brownmink than on white coloured mink (P < 0.001), (3) bite marks applied experimentally byuse of an artificial tooth or occurring due to social/aggressive interactions (bites) betweenmink are only visible if pressure/bite on the mink skin is applied during the active growthphase of the winter coat prior to time when matured, and (4) the longer time mink are keptin groups, the more bite marks can be observed on the skin (P < 0.001).The study has shown that bite marks are a valid and useful welfare indicator for quanti-fying the social tolerance of dark mink and consequently the risk for serious bite wounds.
Applied Animal Behaviour Science, 2014, Vol 158, p. 76-85
welfare indicator; group housing; aggression; mink