Bite marks in mink-Induced experimentally and as reflection of aggressive encounters between mink

摘要

For many years, bite marks have been used as an indicator for aggression in mink production systems. However, the validity of bite marks as indicator of aggression has recently been questioned. 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 produce marks 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 active growth phase of the winter coat prior to time when matured, (3) bite marks will be easier to detect on dark mink than on mink with light coloured fur and (4) the number of bite marks accumulates and increases with time mink are housed in groups. The experimental mink were of the brown colour type (N=140) and the white colour type (N=60). Twenty brown and 20 white mink (housed in pairs since weaning) were housed individually at the age of 16 weeks. Every second week (at the age of 20, 22, 24, 25 and 28 weeks), four brown and four white mink were subjected to pressure by an artificial tooth. Before pressure was applied, each mink was anaesthetized and pain treated. In order to investigate when bite marks from cage mates are inflicted and to what extend they accumulate over time, 120 brown and 40 white juvenile mink were placed in groups of four in climbing cages after weaning. Every second week (at the age of 20, 22, 24, 26 and 28 weeks) group housed mink were moved to single housing in standard cages in order to prevent further bites from cage mates. At the age of 29 weeks, all mink were killed individually by CO2 and the pelts were examined for bite marks. The results showed that: (1) experimentally applied pressure on the skin can be recognized as bite marks in brown mink at pelting, (2) bite marks are easier to detect on brown mink than on white coloured mink (P<0.001), (3) 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 active growth phase of the winter coat prior to time when matured, and (4) the longer time mink are kept in 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 quantifying the social tolerance of dark mink and consequently the risk for serious bite wounds