Bite Marks In Mink Experiment

This article was published with the intention of providing useful information to mink fur farmers. It examines the “validity” of bite marks as a measure of aggressive behavior, which in turn is an indication of the welfare condition of captive mink. Procedures were conducted with a group of experimental mink who were “bitten” with an artificial tooth. Researchers measured various stress responses in addition to the effect of the “bites” on pelts. The article provides useful information for animal advocates, such as baseline levels of “welfare” conditions for mink fur production, and facts about how mink act in the wild.

Fur farming using mink is carried out in standard factory farming conditions. Mink are housed in long, shed-like structures, with rows of cages that hold groups of mink in close quarters. According to this paper, “group housing of mink has become increasingly common because it increases the stocking density and thereby is more economic. […] Group housing is, however, in conflict with the solitary and territorial lifestyle of mink, where the male territory may overlap that of several females in the wild.” These statements clearly indicate that mink farming is more concerned with profit than welfare, but the researchers go on to state that measuring welfare in mink when they are farmed is still a contentious issue. “For many years, bite marks have been used as an indicator of aggression in mink production systems.” They note that “despite the widespread use of bite marks as indicator of aggression, it has neither been tested if bite marks can actually be caused by a bite from a cage mate, nor under which conditions bite marks develop.” It may seem like a semantic distinction but considering that the paper is meant to contribute to fur farming policy, it is a semantic distinction with potentially significant consequences. To test the possibility that bite marks could appear without aggressive interactions, the researchers tested “if, and at what stages of the active growth phase of the winter coat it is possible to produce experimental bite marks in dark and light-colored mink pelts by applying pressure with artificial teeth. Furthermore, we wanted to examine whether the number of bite marks actually accumulated and increased with time in group housing in the susceptible period between the autumn equinox and pelting.”

Using their artificial tooth and a controlled laboratory environment with mink in cages similar to a farm setting, the researchers tested their hypotheses in numerous ways. “All combinations of tooth and pressures experimentally applied to mink produced marks on the leather side of the pelt similar to bite marks inflicted during the growth phase of the winter coat in brown mink,” they noted. “We therefore accept our first hypothesis that experimentally applied pressure to, or even penetration of, the skin during the growth phase of the winter coat will produce bite marks that can be recognized as such at pelting.” They say that “the validity of bite marks as an indicator of bites is documented.” This is perhaps a strange statement for many to digest, as the answer seems completely self-evident. However, the authors more specifically note that “bites inflicted before or after the active growth phase of the hair follicles do not result in bite marks at pelting. Therefore, bite marks reflect social interactions between mink in a time window of about 5–7 weeks.” In a further strange instance of self-evident statement, the researchers note that “bite marks are inflicted by other mink in the cage.” For many reading this, it might seem strange that a controlled experiment was required to figure out what seems obvious to the rest of us.

So, what does this mean for mink and advocates working to end the production of mink for fur? It is hard to imagine that research like this could meaningfully contribute to mink welfare when profit and efficiency are the focus. For advocates, this study offers interesting insider information that can be employed in advocacy and campaigning. These results show that mink attack each other with regular frequency, and that bite marks on the pelts are simply accepted as part of the business for fur farmers, and the industry more broadly. This is perhaps not the most heartening information, but it is material that advocates can add to their repertoire of facts to help the public make more informed, ethical anti-fur choices.

Original Abstract:
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.