ArticlePDF Available

The Welfare of Farmed Mink (Mustela Vison) in Relation to Housing and Management: A Review

Authors:

Abstract and Figures

Early research on farmed mink was predominantly concerned with increased productivity; however, in recent years there have been an increasing number of studies related to welfare. The biology of feral mink has also become better understood, and such knowledge can aid in the assessment of welfare on farms, or in the interpretation of problems related to captivity. This paper is a comprehensive review of research pertinent to the welfare of farmed American mink, Mustela vison, in relation to their housing and management. It indicates how housing conditions might be changed to improve welfare, and where our present knowledge is insufficient. Many significant aspects of mink behaviour in the wild, such as their lack of social contact, their tendency to travel long distances and use several den sites, and regular swimming and diving, are denied them in captivity. Farmed mink also show high levels of stereotypy, suggesting that their welfare is not good. Welfare may be improved by appropriate environmental enrichment and changes in the social environment of farmed mink. In general, studies aimed at improving housing conditions have been limited in scope and outlook.
No caption available
… 
Content may be subject to copyright.
432. Nimon, A.J. and Broom, D.M. 1999. The welfare of farmed mink (Mustela vison) in
relation to housing and management : a review. Animal Welfare, 8, 205-228.
Pre-publication version
!
Abstract(
(
Early!research!on!farmed!mink!was!predominantly!concerned!with!increased!productivity;!
however,!in!recent!years!there!have!been!an!increasing!number!of!studies!related!to!welfare.!
The!biology!offeral!mink!has!also!become!better!understood,!and!such!knowledge!can!aid!in!
the!assessment!of!welfare!on!farms,!or!in!the!interpretation!of!problems!related!to!captivity.!
This!paper!is!a!comprehensive!review!of!research!pertinent!to!the!welfare!of!farmed!
American!mink,!Mustela!vison,!!in!relation!to!their!housing!and!management.!It!indicates!
how!housing!conditions!might!be!changed!to!improve!welfare,!and!where!our!present!
knowledge!is!insufficient.!Many!significant!aspects!of!mink!behaviour!in!the!wild,!such!as!
their!lack!of!social!contact,!their!tendency!to!travel!long!distances!and!use!several!den!sites,!
and!regular!swimming!and!diving,!are!denied!them!in!captivity.!Farmed!mink!also!show!high!
levels!of!stereotypy,!suggesting!that!their!welfare!is!not!good.!Welfare!may!be!improved!by!
appropriate!environmental!enrichment!and!changes!in!the!social!environment!of!farmed!
mink.!In!general,!studies!aimed!at!improving!housing!conditions!have!been!limited!in!scope!
and!outlook.!
(
Keywords:!!animal!welfare,!housing,!management,!mink,!Mustela!vison,!!recommendations,!
stereotypies!
(
(
(
Introduction(
!
There!is!debate!about!whether!or!not!animals!should!be!killed!for!their!fur.!The!personal!
decision!whether!to!wear!or!not!to!wear!a!fur!garment!may!be!different!in!a!very!cold!region,!
where!alternatives!to!fur!garments!are!difficult!to![md,!from!that!in!regions!where!
alternatives!are!readily!available!and!the!fur!is!a!luxury!worn!to!impress!others.!However,!the!
assessment!of!the!welfare!of!fur-bearing!animals!is!independent!of!such!considerations.!
Welfare!refers!to!the!state!of!an!animal!at!a!specific!time!and!can!be!good!or!poor!
irrespective!of!what!people!think!about!the!morality!of!such!usage!of!animals.!If!the!
individual!animal!is!having!difficulty!in!coping!with!its!environment,!or!is!failing!to!cope,!
then!its!welfare!is!poor;!but!if!strongly!preferred!resources!and!opportunities!for!behaviour!
are!available,!and!normal!behaviour!can!be!shown,!then!good!welfare!is!indicated!(Broom!&!
Johnson!1993;!Broom!1996).!A!wide!range!of!indicators!of!welfare!can!and!should!be!used!
when!welfare!is!being!assessed.!The!selection!and!interpretation!of!welfare!indicators!should!
!
THE(WELFARE((OF(FARMED((MINK((!"#$%&'()))*+$,-.)IN(RELATION(( TO(HOUSING((
AND( MANAGEMENT:((( A(REVIEW!
!
A! J(Nimon(and( D( M( Broom!
!
Department!of!Clinical!Veterinary!Medicine,!University!of!Cambridge,!Madingley!
Road,!Cambridge!CB3!DES,!UK!
!
The welfare of farmed mink
least 5 or 6 weeks of age, yet in the wild they remain with their mothers for longer. In a study
of a wild population in Scotland, the first occasion on which a kit was observed outside the
den alone was at 6-7 weeks of age (Dunstone 1993); in another study, kits were weaned,
leaving their natal territory at 11-12 weeks (Gerell1970). On farms, they may be weaned as
early as 5 weeks (Joergensen 1985). This is postulated to be the cause of behavioural
maladaptions, as will be discussed below.
Aquatic lifestyle
Wherever mink occur in the wild there will be water close by, in fact most mink activity in
North America and Europe occurs in water, or within 100-200 m of it (Dunstone 1993). A
radio-tracking study of 19 mink in southern Finland found that both sexes swam distances of
250m almost daily, sometimes twice a day (Niemimaa 1995), and a large proportion of the
wild mink's diet is generally derived from aquatic sources (Day & Linn 1972; Poole &
Dunstone 1976; Birks & Dunstone 1985; Dunstone & Birks 1987; Niemimaa & Pokki 1990,
cited in Niemimaa [1995]; Dunstone 1993). Laboratory studies have found that farm-bred
mink can be trained to retrieve objects from a tank with no reinforcement other than from the
moving cork or cotton reel itself (Poole & Dunstone 1976). Although mink do not see
particularly well underwater (Sinclair et a/1974; Dunstone & Sinclair 1978a), they tend to
retrieve prey by locating it from the surface, then making brief dives of between 5 and 20
seconds and sometimes longer (Poole
&
Dunstone 1976; Dunstone
&
Sinclair 1978b).
Despite the fact that mink seem better adapted to locomotion on land than in water, they have
partially webbed feet, and their swimming speed is much greater than that of terrestrial
mammals and half that of the otter, Lutra /utra (Dunstone 1983; 1993). It seems clear that
swimming and diving are highly significant aspects of the mink lifestyle.
Other behaviours and activity patterns
Mink have been noted for their agility and flexibility (Rice 1967) and for their ability to
climb trees (Burton 1979). Radio-tracking studies of 20 mink (9 male, 11 female) in Britain
determined that mink spent 5 per cent to 20 per cent of the 24h period (on average,
approximately 3h) actively foraging outside their dens; male mink spent just under 2h
travelling, and female mink travelled for around half this time (Dunstone & Birks 1985).
Mink travel within a definable home range. Home range lengths of individual radio-tracked
feral mink have been found to vary from 0.5-5.94 km (Gerell 1970; Birks & Linn 1982),
although Birks and Linn (1982) considered these upper estimates to have been affected by
the behaviour of males with unstable social environments (such males travel distances up to
30km [Niemimaa 1995]). They estimated mean home range length to be between 1and 3km.
A recent study of five mink in eastern Tennessee measured mean home range lengths of
between 5.6 and 11.1km in autumn and early winter (Stevens et a/1997). Mink use a number
of dens within these ranges: Gerell (1970) recorded mink using between two and five dens,
changing dens on successive nights to a den usually 500m distant (although sometimes as far
as 2000m); Stevens et a/ (1997) recorded the use of between 8 and 24 dens per mink, with
overnight trips between them of up to 4300m. Dens are not excavated by the mink
themselves but tend to derive from rabbit holes or natural crevices, for example around tree
roots. Mink favour specific dens rather than apparently similar sites for reasons that are not
evident (Dunstone 1993). Travelling and the use of several den sites are, therefore,
significant components of feral mink behavioural biology. The fact that physical activity is
important to mink has also been suggested by experimental studies showing that caged mink
will run on a wheel for no reward (Zielinski 1986).
Animal Welfare 1999, 8: 205-228
207
Nimon and Broom
It is not known for certain that mink actively defend their home ranges as territories,
however male territories never overlap (Dunstone 1993). Females may tolerate the intrusion
of kits for part of the year, and can on occasion have territories partially overlapping with
males, especially during the breeding season (Dunstone & Birks 1983; Dunstone 1993).
Severe aggression has been reported among unfamiliar adults forced together by captivity
(Rice 1967; Heller & Jeppesen 1986; Dunstone 1993). However, it is possible to keep
captive mink which are familiar with one another together (eg those housed together since
weaning or reared without weaning; see, Social conditions oj housing).
Sensory biology
The mink's anal gland is a major source of specialized odour compounds (Brinck et aI1978).
Mink perform marking by dragging this gland over the ground, or by depositing faeces
(Dunstone 1993). Brinck
et al
(1978) suggested that mink may be able to discriminate
between individuals, and that such an ability may help in detecting intruders in the home
range. Unpublished research (Robinson 1987, cited in Dunstone [1993]) supports minks' use
of scent to identify one another, to distinguish between known and unknown individuals, and
between males and females. Experimental studies have shown that ferrets, Mustela Jura,
have similar capabilities (Clapperton
et al
1988). Gerell (1968, cited in Dunstone [1993])
first noted that mink leave scats in prominent positions within their home ranges, where the
scent is likely to have carried furthest. Dunstone (1993 p 139) states 'the violent reaction of a
mink to the scent of an intruder leaves one in no doubt about the value of a scat'.
Mink are sensitive to lighting conditions, as the processes of fur growth and sexual
development are dependent on exposure to an appropriate photoperiod. Melatonin is the
photoperiodic signal for the autumnal weight increase and moult (Valtonen et aI1995). The
shorter day length controls such changes via melatonin excretion. Other experimental studies
have demonstrated that short day lengths during autumn stimulate spermatogenesis in
October to November, and this effect is enhanced by additional month-long illumination
before the short-day period (Klotchkov et alI985). Jallageas et al (1994) and Gulevich et al
(1995) have further demonstrated that artificial photoperiods can cause significant changes in
mink gonadal function and activity.
The extent
of
modification in relation to captivity
There is anecdotal evidence suggesting that mink on farms have become less fearful and
tamer in response to contact with humans. Hansen (1996) noted that early reports (eg in the
1940s, see Shackelford [1984]) described mink fleeing into the nest box when people were
close by. Hansen (1996) stated that mink now often respond to the presence ofa human with
curiosity. He suggested that nervous individuals might have been eliminated by natural
selection. Hansen's own study (Hansen 1996) involved 3000 farm mink over 6 years in
which he selected and bred mink for exploratory, aggressive or fearful behaviour in the
presence of a human. He found that it was possible to select for fearful behaviour, but not for
exploratory behaviour; in fact those mink selected and bred for exploratory responses
showed a significant increase in fearful behaviour. Thus, while this, and earlier work with
similar results (eg Hansen [1991b]); Houbak [1990], both cited in Braastad [1992]),
suggested that certain behavioural traits may be inherited, no results were achieved which
suggested that farmers could selectively breed for less fearful, and potentially better adapted,
animals.
208 Animal Welfare 1999. 8: 205-228
The welfare of farmed mink
Standard farm housing conditions
Details of standard housing conditions on mink farms appear in Joergensen (1985), Mason
(1991a), M0ller (1991b), and Hansen
et al
(1994). These indicate that mink cages have
approximately 0.27m2(90x30 cm) of floor space, and a height of 30--40 em. A single nest
box, with a floor area of 0.06m
2,
is attached to the cage via a circular hole. The cages are
made of square, galvanized steel mesh, allowing faeces to fall through, and the nest boxes
are generally made of wood, but may have a mesh roof. Drinking water is continuously
available via an automatic system: a drinking nipple inside the cage is attached to a hose. The
water is protected from freezing via a circulation or heating system. Mink are fed once or
twice a day with a nutritious puree that is placed on top of their cages.
Cages are made in six- or eight-cage sections (joined side-by-side) and placed in rows in
sheds. Sheds generally contain two or more parallel rows, with a roof above and walls which
are either left open or filled in with wire mesh (Mason 1991a) or a screen made of heavy
plastic or sacking stretched on wooden frames (Joergensen 1985). Joergensen (1985 p 38)
recommends that a hedge be grown around the sheds for 'cold does not affect mink, but
draught is their worst enemy'.
After weaning (usually at approximately 7 weeks of age [Mason 1996]), mink may be
housed individually, or placed in male/female sibling pairs in one cage. They stay this way
until pelting, at approximately 8 months of age. At this point, some individuals may be
selected for breeding purposes and rehoused.
It is clear that the housing conditions of mink on farms differ markedly from those of
mink in the wild in terms of the rearing of kits, the proximity of other mink, and the
opportunities for swimming and diving, roaming, using different dens, and engaging in
physical activity. Undoubtedly, the olfactory environment and lighting conditions on farms
also differ greatly from conditions in the wild.
Health and disease on mink farms
Mink have been described as 'extremely hardy' (Rice 1967 p 73) and 'healthy vigorous
animals [that] rarely get sick if they have adequate food, water and clean conditions'
(Dunstone 1993 pp 183-4). The incidence of disease appears to be relatively low: Wahlstrom
(\987, cited in Harri et al [1995]) reported that the summer mortality rate on 16 farms in
Sweden averaged 1.3 per cent for adult males, 1.5 per cent for adult females and 2.1 per cent
for kits. Joergensen (1985) recommended that good housing conditions include well-spaced
sheds and that good hygiene should involve both cleaning and disinfection to prevent manure
and dirt from becoming chronic reservoirs for viruses and bacteria. It is further
recommended that farmers be vigilant and regularly (eg daily) inspect their mink for any
signs of disease.
Disease is always a threat. Rice (1967) considered that there are three diseases which, if
introduced, will seriously deplete a colony: botulism, distemper and Aleutian disease.
Botulism is said to occur only infrequently, but when it does occur, the powerful toxin
produced by the anaerobic bacterium Clostridium botulinum can cause widespread mortality
throughout a colony. Only a small portion of infected food may kill a mink. Distemper is
also very infectious and will easily spread from one infected mink to the majority of the
colony during the 8-14 day incubation period. One-time vaccination can protect animals
from these diseases for life; however, Joergensen (1985) noted that vaccination is costly, and
the act of vaccination may risk spreading disease via infected syringes. He recommended
Animal Welfare /999, 8: 205-228 209
Nimon and Broom
frequent cleaning under cages, and disinfecting of sheds, while the decision to vaccinate is
consIdered and made on an annual basis.
Aleutian disease can be a major cause of mortality, and there is no treatment for infected
animals. Investigations involving over 5500 autopsies in Argentina indicated that Aleutian
disease was the most important cause of premature death (Martino
et al
1991). Airborne
transmission may be substantial, although mechanical transmission is probably more to
blame (Jackson
et al
1996a). Jackson
et al
(1996b) reported that transmission may be
enhanced by the use of contaminated toenail clippers for blood collection. Farmers can,
however, test for the disease and cull infected animals from the stock (Dunstone 1993).
Nursing disease is also reported among adult female farmed mink in Europe (M011er
1991b). A study of the pattern and relative frequency of diseases in adult female mink during
the lactation period on 48 farms in southern Ontario found that nursing disease was the most
common diagnosis (56%), the mortality rate among this group ranging from 0.2 per cent to
10.1 per cent, with a median of 1.9 per cent (Schneider & Hunter 1993a). Variation between
farms was associated with the type of water source, size of the farm and source of feed
(Schneider
et al
1992). It has also been suggested that nursing disease may result from
energy depletion due to lactation (Schneider & Hunter 1993b).
While farmed mink may be relatively hardy, there exist no published reports of the
incidence, causation and appropriate prevention of disease among farmed mink in Europe.
Harri et al (1995) examined the possibility that farmed mink experience a high incidence
of stomach ulcers. An incidence of ulcers in 35 per cent to 40 per cent of kits, and in 55 per
cent of adults, was reported by Wahlstrom (1987, cited in HaITiet al [1995]). This result was
then cited to demonstrate that approximately half of all farmed mink have ulcers, and to
conclude that ulcers were the result of stress and an inability to cope with farm conditions
(Kollberg & Bjorkland 1989, cited in Harri
et al
[1995]). Examining singly housed mink
under standard conditions, Harri
et al
(1995) found a lower incidence of stomach ulcers
(24%). Most of these ulcers rated only one on a five-point scale of severity. However, the
study also found that mink subject to aversive treatments (such as frequent, regular
immobilization in a restrainer) failed to develop significantly more ulcers than control
animals. They concluded that the incidence of stomach lesions was not a useful indicator of
poor housing conditions.
The nest box
As discussed above, wild mink use a number of den sites, change dens daily, and prefer
particular dens for as yet unidentified reasons. This would suggest that the presence of at
least one nest box is essential. Results from Hansen (1988) suggested that male and female
mink housed in standard-size cages without nest boxes had poorer fur quality than those with
access to nest boxes. This was thought to result from their lying against the wire mesh, and
from the inhibition of blood circulation and nourishment of the hair follicles due to
additional heat loss. Reduced fur quality can be considered a sign of poor welfare - and an
indication that an animal is having difficulty in coping. Results also suggested that the
absence of a nest box might lead to an increased metabolic rate and higher adrenal weights.
The latter effect may indicate chronic stress, reflecting the adrenal gland's capacity for
cortisol secretion (Mason 1992).
Determining the effect(s) of captivity without access to a nest box on physiological
parameters in mink has been complicated by results which could support contradictory
hypotheses (Hansen
&
Brandt 1989). However, later investigations (Hansen & Damgaard
210 Animal Welfare 1999,8: 205-228
The welfare of farmed mink
1991a) showed that male and female mink in standard cages without nest boxes had a lower
level of circulating eosinophil leucocytes than mink with nest boxes - a reaction seen in
mink subjected to acute immobilization (Heller & Jeppesen 1985). The effects of the absence
of a nest box were comparable with those produced by 30-min immobilization sessions.
Furthermore, female mink housed without nest boxes also had higher cortisol levels than
those housed with nest boxes. In another experimental study, female mink deprived of nest
boxes during the whelping period were found to lose significantly more kits than other
experimental groups, and weight gain among their kits was significantly lower (Moller
1990).
Hansen et al (1992; 1994) found that female mink in cages without nest boxes showed
more stereotypic behaviour than those housed with nest boxes. They considered that this
might arise from frustration at the inability to avoid contact with neighbours. These mink
also had a greater food intake which did not result in more rapid, or greater, weight increase.
Hansen et al (1992) stated that the growth rate was higher in mink housed with nest boxes,
although it is unclear how this was measured. These results accord with those of Hansen
(1988), ie that mink housed without nest boxes had a higher metabolic rate.
The importance of the nest box for the health and welfare of farmed mink has now been
amply demonstrated for both male and female animals. No further experimentation should
deprive mink of this basic necessity. Rather, any further experiments could examine how the
provision of nest boxes might be improved: for example, work by Moller (1990) suggested
that a 'drop-in' bottom (ie a false bottom) in the nest box was associated with better kit
survival than in standard nest boxes. He supposed that this made it easier for a mink to keep
her kits from wandering and, thus, protect them from hypothermia. An obvious further issue
for investigation is the preference of mink for more than one nest box (see below).
Drinking
water
Moller (1991a) identified three points with regard to the provision of drinking water for
mink. i) Water must be available 24h a day, for captive mink drink frequently, day and night.
Standard farm conditions meet this recommendation (as above). ii) While water is often
circulated so as to prevent it freezing and becoming inaccessible, it may reach high
temperatures in summer. iii) The water intake of mink and kits during the female's lactation
period is an important issue. Moller's observations showed that kits began to eat food at 4
weeks of age, but did not begin to drink water until 6 weeks of age: therefore, their moisture
requirements must be met via food, milk, and licking the mother's saliva. During this period,
Moller (1991a) noted that females may experience dehydration, and weight loss (particularly
during hot summers), and that 'nursing disease in the female and cannibalism among the
kits' (Moller 1991a p 5) occurs. He concluded that the earlier kits begin to drink, the greater
the relief for the mother and her kits.
Supplementary watering systems
It was not possible to determine how widespread or serious the problem of potential kit and
mother dehydration may be in Europe. However, it is clear that water intake during the
lactation period is an important issue that warrants investigation. Moller (1991a) noted that
mink will drink from an open water surface but have no natural inclination to drink from the
valve in the cage, and that various devices have been used to teach kits how to drink water.
He tested the effect of a supplementary watering system - a 'drip' watering system, which is
described by Joergensen (1985) as a tube dripping water into drinking cups. Experiments
over 2 years, involving two groups of 60 mink families each year, indicated that kits
Animal Welfare /999, 8: 205-228 211
Nimon and Broom
provided with this supplementary system made significantly fewer unsuccessful attempts to
drink than those provided with just the standard nipple system. The behavioural observations
conducted in the second year indicated that kits with the drip watering system began to lick
water from around 40 days of age. In the first year, there was no difference in weight gain
between experimental and control groups; but in the second year, kits in the experimental
group were reported to gain weight significantly faster, and females to lose significantly less
weight, than those in the control group. Joergensen suggested that the difference in results
between these two years might be due to the higher average temperature in the second year
(2.1°C higher). The benefits of supplementary watering systems may, therefore, be greatest
when the summer is especially hot. M0ller (l991a) concluded that it is important to provide
supplementary systems for helping kits to drink before they are able to activate nipple
systems.
M0ller and Hansen (1993) examined minks' use of a spray watering system which, when
activated on a timer, produces a jet of water. This is said by the manufacturer to provide a
shower for the mother and extra water on her pelt for the kits to lick (thus supplementing
their water intake). In experiments involving two groups of almost 100 animals, the spray
watering system was switched on for 30-60 s at a time, four times each day. The results
showed that while the majority of the females used the spray for at least part of the time it
was available, there was no positive effect on the weight of the females. This, they
suggested, might have been due to the effect of low temperature, and the possibility that
benefits are greatest when temperatures are highest. Kits did, however, gain weight more
rapidly. This effect was probably because kits licked water from the cage and floor after
spray watering: they did not lick water from the female's pelt. In another experiment
(Hansen 1990), the provision of a 2cm-deep water tray in the cages of lactating females did
not affect weight change in the mother. However, the lack of positive effect may have arisen
because the female was reported to routinely empty the tray of water by getting into it.
The provision of supplementary watering systems would appear to be problematic, given
that commercially available products have produced varying results, and that certain claims
made by manufacturing companies as to how mink will behave in relation to their equipment
are incorrect (eg M0ller & Hansen [1993]). The issue of mother and kit dehydration, and
how to provide readily available supplementary watering systems, is a continuing problem.
Drinking water temperature
M0ller (1991a) also investigated minks' drinking water temperature preferences in
experiments which gave the animals a choice between cool (6°C) or warm (40°C)
temperatures. His results showed that mink accepted, and sometimes preferred, drinking
water at temperatures up to 40°C. He reported that similar results have been found with rats.
In fact, he argued, mink may prefer cold or warm water under different circumstances. A
preference for warm water may occur when a mink is dehydrated, as cold water is let out of
the stomach only slowly, and the stomach is filled quickly. While the feeling of thirst is
satiated, the animal is not as well hydrated. Water at body temperature passes through the
stomach, allowing a greater volume to be ingested before stomach distention signals a
satiation of thirst. On the other hand, cold water may be useful when the temperature is high.
According to M0ller (1991a), mink may die from heat exhaustion in temperatures of30°C or
more. Rats drinking cold water (eg at l2
0
C) have been shown to lower their body
temperature by up to 1.2°C (Deaux & Engstrom 1973): thus, the opportunity to cool the body
may also be useful for mink. However, more experimentation is needed to provide
conclusive evidence regarding water temperature preferences in mink, and whether these
212 Animal Welfare 1999, 8: 205-228
The welfare of farmed mink
proposed benefits of hot and cold water might indeed be applied so as to benefit captive
mink.
Stereotypies
and
enrichment
Stereotypies are repetitive, invariant behaviour patterns with no obvious goal or function
(Mason 1991 b). Their occurrence is often associated with barren and restrictive conditions,
or environments which might be considered suboptimal, and they develop in animals faced
with insoluble problems of frustration or conflict (Hinde 1970; Mason 1991b). Once
developed, stereotypies can be elicited independently of the original stimulus, becoming part
of an animal's behavioural repertoire.
Some authors have argued that stereotypic behaviour may be an adaptive response to an
aversive situation (eg, see Hansen et al [1992]), and some results suggest that farmed mink
showing high levels of stereotypy are, in other respects, coping better with their
environment. For example, in one study, it was concluded that highly stereotyping female
mink had lower baseline levels of plasma cortisol than those showing low levels of
stereotypy (Bilds0e et al 1991), although it is not entire Iy clear that their results supported
such a conclusion. Also, signs of poor welfare, such as low body weight, do not necessarily
correlate with stereotypy levels in adult mink (Mason 1991a; 1992; 1993), although in kits,
the level of stereotypy was found to be negatively correlated with body weight, and
positively correlated with the mean size of the adrenal gland (P
<
0.05 in both cases [Mason
1992]). While it is possible that those individuals performing stereotypies might be better off
in some respects than those which do not (since individuals have widely differing ways of
reacting to aversive stimuli [Broom
&
Johnson 1993]), the very existence of stereotypies
indicates an inadequate environment in which mink are having to do much to cope.
Furthermore, exposure to aversive stimuli, such as restricted feeding and daily
immobilization sessions, has been shown to lead to an increase in stereotypies in farmed
mink (Bilds0e et aI1991), indicating that stereotypies arise from aversive environments even
if they are eventually elicited under different circumstances. Performance of stereotypies is
also associated with negative consequences, such as slower growth in kits (Mason 1992;
Mason
et al
1995) and increased feed intake without a consequent increase in growth
(Hansen
et al
1992). In contrast, studies of both mink and other farmed or captive animals
suggest that stereotypies can be ameliorated by improving the animals' environment, for
example, via enrichment (eg increasing the size and complexity of the environment [Fraser
1975; Odberg 1987; Bryant et a11988; Markowitz et a11995; Cooper et aI1996]). Although
stereotypies, and aberrant behaviour such as tail biting, appear to have a genetic component
(eg Hansen [1993]; de Jonge [1988; 1989], cited in Mason [1994]), it is apparent that
learning and environment can affect the occurrence of stereotypies.
Stereotyped behaviour is widespread among farmed mink. In a study of 142 singly housed
female mink, de Jonge
et al
(1986) found that 70 per cent of them performed stereotypies to
a greater or lesser extent, and 50 per cent did so for greater than 25 per cent of the time they
spent awake. In a study of 187 male and female mink, Bilds0e
et al
(1990a) found that
stereotypies accounted for an average of 15.8 per cent of active behaviour. Levels of
stereotypy vary between individuals, from farm to farm, and from season to season (Bilds0e
et aI1990b), but are an ever-present feature of farmed mink behaviour. Wild mink, mink in
zoos and mink in enriched laboratory conditions do not show these abnormal behaviours (eg
Dunstone [1993]; Erlebach [1993]). This is a strong indication that standard farm conditions
are inadequate and should be improved for the sake of mink welfare. The following sections
Animal Welfare 1999, 8: 205-228 213
Nimon and Broom
examine improvements to the cage environment, and note how these may be related to
stereotypies.
Feeding regimes
It is often reported that stereotypies are at their peak in fanned mink prior to feeding (de
Jonge et a11986; Bilds0e et a11990a; Mason 1991a; 1993), and it has been suggested that
food deprivation (Bilds0e et al 1991) and minks' inability to access food at will are
significant factors in producing stereotypies. In fact, Rushen and de Passille (1992)
considered that most stereotypic behaviour reflects inadequacies in feeding regimes, rather
than in housing. Hansen et al (1994) observed stereotypic activity among fanned mink which
were fed ad libitum, and thus should have experienced no frustration at the lack of food: in
these mink, stereotypy occurred mainly at night and after feeding. However, this study did
not involve a control group which might have indicated whether ad libitum feeding reduced
the incidence of stereotypies. Nor has research examined whether ad libitum feeding will
prevent the occurrence of stereotypies in mink which have not yet learned to stereotype.
If fanned mink stereotype because of their lack of control over their environment,
particularly in relation to feeding, then measures aimed at increasing individual control may
improve mink welfare and reduce stereotypies. For example, caged mink have learned to
work for food, by running on a wheel and earning pellets at varied work:reward ratios
(Zielinski 1988). Shepherdson
et al
(1993) found that providing food to zoo-housed small
felids in a way that maximized the functional consequences of foraging behaviour (eg
requiring cats to hunt for food) reduced the incidence of stereotypy and increased
behavioural diversity. Evidently, such a change in feeding regime would require substantial
changes in farm management in relation to the type of food delivered, but further research
could explore the potential benefits of permitting caged mink greater control over their
feeding regime, after which point the feasibility and practicality of such a change could be
assessed.
Stereotypies in farmed mink are, however, unlikely to derive from pre-feeding frustration
alone, as post-feeding stereotypic behaviour occurs even in very young mink. Furthermore,
Mason (1993) has pointed out that the form and timing of the occurrence of certain
stereotypies (eg head twirling) suggests that they are more likely to be derived from attempts
to escape the cage, thus suggesting that the physical conditions of the cage are inadequate.
Cage size
Research does not suggest that increases in cage size in the absence of further enrichment
improve the welfare of farmed mink. Jonasen (1987, cited in Hansen [1988; 1991a])
conducted experiments using six- and eight-room cage sections (ie six or eight contiguous
cages in a 2m section) and found no difference in the frequency of stereotypies associated
with the different cage sizes. This result was replicated in a repetition of the same experiment
with pairs of kits. Hansen (1988) studied the behaviour of 228 mink kits housed in pairs in
bare wire cages with floor areas of 1.05m2(large), 0.27m2(standard) and 0.lm2(small). He
found that stereotypies did not occur significantly less often in the largest cage size, only that
cage size influenced the type of stereotypy. In addition, he found significantly higher adrenal
weights among the mink kept in the larger cages, suggesting that this treatment may have led
to higher stress levels. Later work (Hansen et aI1992) on 60 male:female pairs in cages of
these same sizes found that mink in the larger cages performed significantly more
stereotypies, and had a significantly lower level of circulating eosinophil leucocytes, than
214 Animal Welfare 1999. 8: 205-228
The welfare of farmed mink
those in small or standard cages. The measurement of eosinophil levels is not easy to
interpret because a variety of factors affect these levels, although they can indicate stress in
some circumstances. This suggests that, within the size range tested, mink given larger floor
areas in barren cages had no better (or perhaps poorer) welfare than those in standard cages.
The smallest cage size was also found to inhibit the performance of scent-marking and
climbing. Hence, mink showed fewer of their natural behaviours in the small cages, and
could be said to experience poorer welfare than those in standard cages.
Environmental enrichment
Markowitz (1982) introduced the concept of environmental enrichment for zoo animals, in
which the cage environment was modified to provide appropriate contingencies for the
performance of natural behaviours not otherwise observed. For example, gibbons, Hylobates
spp., were able to earn food by swinging on a series of artificial vines. Enrichment, or the
improved biological functioning of captive animals resulting from modifications to their
environment, has since become a general concern in animal welfare research (eg Newberry
[1995]). A few studies have examined the consequences for farmed mink of enrichment-
oriented modification of the standard cage environment.
Additions to the standard cage environment
Hansen (1990) compared the behaviour of female mink in standard cages during whelping
with those in cages enriched by the addition of a suspended wire-netting cylinder. Females in
the enriched cages showed a significantly lower incidence of stereotypic behaviour, and it
was suggested that the cylinder provided a resting place, where the mother could escape her
kits temporarily: there was a decrease in the use of the cylinder when the kits were 7-8
weeks old and able to reach their mother there. Later work (Hansen et al1994) attempted to
examine the potential enrichment benefits of wire-netting cylinders, in conjunction with
increases in cage size, for adult mink without kits. However, the increase in cage size (from
small to large, as in Hansen [1988]) involved cages which either had no nest box, or had nest
boxes and wire-netting cylinders. Hence, the effects of enrichment were confounded by the
effects of the presence or absence of a nest box. Thus, it is not known whether a suspended
wire-netting cylinder would reduce stereotypic behaviour in mink other than lactating
females housed with kits. Nor is it known whether a larger cage floor area (eg 1.05m2)in
conjunction with one or more wire-netting cylinders would produced less stereotypic
behaviour than a standard cage enriched with such a device.
Jeppesen and Falkenberg (1990) examined the effect of introducing toys into the standard
farm cage environment. Mink kept in male:female pairs were given two, hard, red, 4.5cm
(diameter) balls for a period of 1 month. The toys had no effect on physiological measures
(eg eosinophil or cortisol levels), on the extent of bite marks recorded on pelts, or on levels
of stereotypy, although the method of recording mink behaviour (involving an observer close
to the cages) may have reduced the incidence of stereotypic behaviour. Mink spent time
manipulating the balls (ranging from 15% of all observations in the first 24h, to close to zero
after 27 days), and lasting effects were detected in terms of higher levels of non-stereotypic
activity, and greater 'curious(ness)'. Thus, the introduction of balls might be regarded as
having caused a limited improvement in welfare, although no overwhelming effect can be
inferred from the one-time introduction ofa single type of toy. Newberry (1995) has warned
that toys intended for environmental enrichment should have relevance to the animals'
natural behaviour: while balls would seem appropriate to elicit chasing and pouncing, it
Animal Welfare 1999. 8: 205-228 215
Nimon and Broom
appears that part of the appeal of this toy derived from its novelty value, which reduced
substantially over the trial period.
Wider-ranging enrichment
Just as it has been noted that stereotyped behaviour does not occur in the wild, there is
evidence to suggest that such behaviour may be absent among mink kept in highly
naturalistic enclosures. Erlebach (1993; 1994) compared the behaviour of mink kits
individually housed in standard cages with those living with their litter in large enclosures
(8x5.5x2.5 m
[lxwxh])
in which the ground was formed of soil and sand, and the enclosure
contained natural vegetation, climbing branches, tunnels, nest boxes, and a concrete
waterpool (2x2xO.6 m
[lxwxdJ)).
The author reported that all cage-housed mink developed
running stereotypies, whereas no such behaviour occurred in those housed in the enriched
enclosure. The enclosure-housed mink played for 13.8 per cent of all observations, but play
among cage-housed mink was significantly lower (1.7%). Enclosure-housed mink were also
observed using climbing branches. The effects of enrichment and the social conditions of
housing were confounded, but the results suggest a substantial difference between the
standard cage environment and a naturalistic enclosure for kit development. In a study of zoo
housing of the stoat, Mustela erminea - another asocial mustelid - no mention is made of
stereotypic behaviours among individuals housed in enclosures containing artificial rocks
and vines (DonCarlos et al 1986). Given that the goal of this project was to increase visitor
enjoyment of the stoat exhibit, one might assume that behaviours of such unpleasant
appearance would have been mentioned, had they occurred. Research with bank voles,
Clethrionomys glareolus, has shown that stereotypies rarely develop among animals kept in
large enclosures enriched with items such as intertwined twigs (Odberg 1987).
Recent, experimental investigations involving preference testing offer the best potential
method of defining appropriate housing for captive mink. Cooper and Mason (1997b)
studied 8-month-old farm-reared kits in an apparatus consisting of a standard farm cage
connected to seven compartments, each containing one of seven resources. The mink visited
all the compartments. In order of preference, they spent 52 per cent of their time in the home
cage and connecting tunnels; 36 per cent of their time in a hay box (intended to represent an
alternative den site); 4 per cent of their time in a bath (standard human-size); 2 per cent of
their time, respectively, with a novel object (changed daily), a prey-like toy, a raised
platform and a tunnel; and 0.3 per cent of their time in an empty compartment. However, the
true importance of these resources to the mink was indicated not by how much time they
spent with each, but by how hard they were prepared to work to spend time with each. This
was measured by gradually increasing the weights on the access doors to each compartment
until mink ceased seeking access to resources. All mink overcame a weight of l250g in order
to visit the novel object and the bath, whereas no mink overcame weights of 750g to visit the
empty compartment, 1000g to visit the tunnel, or 1250g to visit the toys or platform. Overall,
consumption of resources in terms of both highest 'entry fee' paid, and time spent with the
resource, indicated that mink ranked the hay box, bath and novel object as most important,
with the toys, tunnel and platform less important, and the empty compartment of minimal
importance. This rank ordering of the resources by mink supported earlier experimental
results (Cooper & Mason 1996) and another study, in which the hay box, bath and novel
objects were three of the four most important resources (Cooper & Mason 1997a, c). The
preference for the resources existed even though the mink had been reared in wire cages
without novel objects or swimming opportunities. Recently, an experimental investigation
allowed farmed mink access to a swimming basin the size of a human bath for a year or more
(Skovgaard et al 1997). However, these researchers concluded only that the litter size of
216 Animal Welfare 1999, 8: 205-228
The welfare of farmed mink
these mink was not significantly different from that of controls: such results suggest little
about the welfare of mink.
As described earlier, wild, feral mink make use of several dens and their lifestyle is highly
involved with water. These results, suggesting that mink will work hard for access to an
alternative nest box and a bath large enough for swimming, are, therefore, not surprising. It
also appears that mink seek a degree of novelty in their environment: this concurs with the
findings of Jeppesen and Falkenberg (1990), indicating that the use of balls for play was
highest when the objects were first introduced and thus, had the greatest novelty value.
These studies indicate that captive mink can benefit from environmental enrichment. With
regard to the effect of environmental enrichment on the amelioration of stereotypies, it is
possible that such an effect would be limited in adult mink, once stereotypies had already
developed. Cooper et al (1996) found that stereotypy was harder to prevent by environmental
enrichment in older bank voles. By transferring voles from barren cages to enriched cages,
they were able to show that young voles ceased stereotyping, yet older voles continued to
show stereotypic behaviour, supporting Mason (1991 b)' s hypothesis that stereotyped
behaviour becomes harder to disrupt with time. This may be true of mink also, as several
papers have emphasized the importance of rearing conditions in the development of
stereotypies in mink (see, Kit age at weaning). Similarly, Marriner and Drickamer (1994)
concluded that rearing conditions were more important than present environmental
conditions with regard to the occurrence of stereotypies in captive primates. The effect of age
in relation to mink stereotypies and environmental enrichment is, therefore, unknown at
present.
Social conditions of housing
Housing individually or inpairs or groups
After weaning, mink kits may be housed individually or placed in male:female pairs. Given
that wild mink live in large territories which generally do not overlap, and that they have
been reported to be extremely hostile when brought into close proximity with unfamiliar
adults, there has been some debate about the most appropriate social housing conditions for
mink. When mink are housed together on farms, however, this generally occurs at or soon
after weaning. A number of experiments have compared different social housing conditions
for mink.
Heller and Jeppesen (1986) compared individual housing of kits with housing in pairs or
triplets. At the age of 8 weeks, 50 male and 50 female mink were transferred to one of four
housing conditions (male and female housed singly, male:female pairs, male:male pairs and
groups of three females). Blood samples were taken regularly, and all social groups showed
higher circulating eosinophil leucocyte levels than individually housed animals until the
animals were 6 months old. They also reported that females housed with other mink had
higher eosinophil levels than when housed alone. Hansen and Damgaard (1991b) examined
the effect of individual housing versus housing in groups of three males and three females in
larger cages (floor area 1.05m
2)
on a number of haematological variables and pelt quality in
168 kits. They found no difference between males under the two conditions, but results again
suggested that females kept with other mink may experience more stress than females housed
alone: both cortisol concentration and the frequency of bite marks were higher in these mink.
However, the same problems were not found to be associated with housing in pairs.
Damgaard and Hansen (1996) compared individual housing with housing in pairs from
weaning to pelting in 96 kits equally divided between the two conditions. They found no
evidence of problems - as indicated by the heterophil:lymphocyte ratio - to suggest any
Animal Welfare /999, 8: 205-228 217
Nimon and Broom
difference in welfare between the two groups, for either males or females. The level of total
leucocytes was significantly higher in group-housed mink than in singly housed mink, which
the authors suggested might indicate a greater immune response in group-housed mink. Mink
kept in pairs had better pelt quality and, surprisingly, did not have a significantly higher
incidence of chew or bite marks on their skins. Similarly, M0ller (I991c) studied mink kits
kept singly or in pairs from weaning to pelting. He found no statistical difference in the skin
quality between the two groups, despite finding that individually housed kits were lower in
weight at pelting and had shorter skin length, a situation which would be expected to result in
higher quality skins. The fact that individually housed kits showed lower weight gain than
kits housed in pairs may not have been due to housing conditions, given that those kits
housed individually weighed less from the outset and initial weight at rehousing was
significantly related to weight at pelting. Similar studies (eg S0nderup [1990], cited in
Damgaard
&
Hansen [1996]) have not found this effect of housing on weight. However,
these results do suggest that mink housed in pairs have no worse, and possibly better, welfare
than those housed individually.
Studies by de Jonge (1996a, b) and de Jonge and van Iwaarden (1995) have led them to
conclude that housing mink in groups in bigger cages is an economically sound choice.
Contrary to the results of Hansen and Damgaard (1991b) and de Jonge (1996a), they found
that pelt quality was not clearly influenced by group-housing, and damage to the pelt
corresponded more closely with the mink density per cage, than the size of the group. With
regard to welfare, de Jonge and van Iwaarden (1995) raised 37 litters of mink without
weaning: instead they remained with their mothers in housing consisting of three connected
traditional cages. These animals were reported to grow up without fighting, and their mothers
stayed healthy. According to the results, these mink had a normal size and a better pelt
quality at auction when compared with mink housed in male:female pairs.
Some anecdotal observations suggest that a familiar partner may provide some degree of
environmental enrichment for a farm kit. Hansen
et al
(1994) mentioned that kits housed in
pairs preferred to lie together regardless of the cage size or the presence of the nest box.
Damgaard and Hansen (1996) remarked that living alone in a barren, static environment
increased stereotypies in farmed mink. Jeppesen
et al
(1990, cited in Braastad [1992])
reported that individually housed mink kits kept in single cages developed stereotypies
earlier and with a higher frequency than kits kept in pairs. Although Erlebach (1993) made
observations relating to a very small sample in this respect, she also reported that running
stereotypies appeared earlier in individually housed mink than in those housed in groups of
three. She suggested that the presence of playmates might have delayed the development of
stereotypies.
There is a discrepancy between the results of Heller and Jeppesen (1986) and those of
later studies. This early work involved a relatively small sample size in some comparisons
(eg 20 kits only housed in male:female pairs), and it is possible that later studies, with larger
sample sizes, are more reliable. Two studies (Heller
&
Jeppesen 1986; Hansen
&
Damgaard
1991b) suggested that females housed in groups showed some signs of poorer welfare than
individually housed females. However, there is also evidence to suggest that pair- and group-
housed mink of both sexes fare no worse, or even better, than mink housed individually. Fur
quality may be better in mink housed in pairs, and the presence of another kit from the time
of weaning may provide enrichment for mink, although adequate behavioural studies have
yet to be conducted.
218 Animal
Welfare
1999,
8:
205-228
The welfare of farmed mink
The effects of visual isolation
The solitary nature of wild mink suggests that visual contact with other mink may also lead
to poor welfare on farms. Experiments have generally focused on whether visually isolated
females will have higher breeding success.
Gilbert and Bailey (1967) separated 54 farmed mink into two groups, one of which was
visually isolated by placing fibreboard partitions between individual cages, and one of which
was housed under standard conditions. From early January until mid-March, there was no
visual contact between mink in the isolated group. They found that visual isolation seemed to
inhibit ovarian development in comparison with the control group, a result that they
attributed to a lack of social facilitation. Similarly, Gilbert (cited in Gilbert & Bailey
[1969b)) found that mink which were visually isolated in the long term (ie for 4 months)
showed inhibited gonadal stimulation and follicle development: in extreme cases the females
did not come into oestrus.
However, Gilbert and Bailey (1967) suggested that isolation may have been beneficial
after mating, because females did not engage in agonistic encounters with neighbours, and
thus may have enjoyed better welfare. Isolates had a slightly lower number of stillborn kits
(although no statistical test was employed), and it was suggested that increased litter size
might result from visual isolation. Later experiments (Gilbert & Bailey 1969b), using 44
female mink under the same conditions, found that the control females showed greater body
weight losses during oestrus and pregnancy (or pseudo-pregnancy) than isolates. However,
physiological parameters (eosinophil leucocyte levels) indicated that visually isolated mink
may have had poorer welfare during anoestrus. They concluded that visual isolation during
anoestrus may be detrimental to farmed mink, whereas isolation during oestrus and
pregnancy appeared to be beneficial.
In another study of the breeding success of 102 females of three different mink varieties,
Gilbert and Bailey (1970) found little overall difference between isolates and controls,
although a significant increase in litter size only resulted from visual isolation of the 'dark'
strain. This result was attributed to the particular nervousness of this strain, with the
suggestion that isolation reduced stress induced by conspecifics and thus limited in utero loss
of kits. In larger-scale experiments, Moller (1991b) also found little evidence of an
improvement in breeding success achieved via visual isolation, although it is not clear
whether visual isolation 'by means of an empty cage' (Moller 1991b P 39) achieved the same
degree of isolation as the use of board partitions. In the one experiment reported by Moller
(I991c), which involved visual isolation by means of filling the adjacent cage with straw,
isolated females gave birth to significantly more kits - although no difference in litter size
was apparent 2 weeks later.
Behavioural observations relating to the potential effects of visual isolation on welfare are
limited. Moller (1991b) reported that the control mink in his experiment were much more
active during all time periods than isolated females, although the type of activity and its
significance were not discussed. Vestergaard (1983) reported that visually isolated females
differed from controls in showing no aggressive or stereotyped behaviour. De Jonge
et al
(1986) suggested that adjacent animals adjusted their activity patterns so as not to be active
simultaneously.
In conclusion, while the visual isolation of females may not lead to better production
results, and long-term visual isolation in singly housed mink may have adverse effects, little
research examining whether visual isolation may improve welfare, at least for limited
Animal Welfare 1999, 8: 205-228 219
Nimon and Broom
periods, exists. What evidence there is, indicates that isolation may improve welfare in
females during oestrus and pregnancy. The effects of visual isolation from unfamiliar
animals among mink housed in familiar pairs or groups are unknown.
Kit age at weaning
Mink kits on farms become nutritionally independent of their mothers by 5-6 weeks of age.
If this accurately indicates kit development in nature
I,
then the question arises as to why kits
do not leave their natal territory until they are approximately 12 weeks old. Recent, as yet
unpublished, research has attempted to answer this question. Gimpel (1997) examined the
role of the mother as a 'secure base' for exploratory behaviour, in a manner similar to studies
regarding contact with mothers and exploration in rhesus monkeys, Macaca mulatta (eg
Harlow & Zimmerman [1959]). Using kits from six litters, she measured their latency to
explore, amount of time spent exploring, attempts to return to the rest of the litter, and
distress calls, when they were with a littermate or their mother. Between the ages of 8.5 and
13.5 weeks (ie the time between when they would be weaned on a farm, and when they
would be weaned in the wild) kits made more attempts to return to the home cage and gave
more distress calls when with the littermate; there was also a trend towards decreased latency
to explore when the mother was present. These results suggest that, following nutritional
weaning, mothers are important to kits as they learn to explore and interact with their
environment.
Research results have shown that age at weaning can influence the later development of
aberrant behaviours, such as stereotypy and tail biting. Mason (1996) used kits from 53
litters: one from each was weaned at 7 weeks, in accordance with standard farm procedure,
while another was weaned at 11 weeks. She compared the development of stereotypies in the
two groups, and found that the earlier-weaned group spent significantly more time
stereotyping (44% versus 23%), and that their stereotypies also consisted of a greater
proportion of completely fixed sequences. Tail biting, which has been shown to occur in
approximately 20 per cent of farmed mink in the Netherlands (de Jonge [1989], cited in
Mason [1994]), is significantly higher among male mink removed from their mother at 7
weeks of age, than in those left with their mothers for 6 months (de Jonge [1988; 1989], both
cited in Mason [1994]). Mason (1994) examined male and female kits removed from their
mothers at either 7 or 11 weeks of age, and found that earlier-weaned females showed a
significantly greater tendency to tail bite than later-weaned females; the same trend was still
evident in both sexes at 10 months. On the basis of kits' immediate reactions to weaning
(distress calls, changes in the number of eosinophil leucocytes), Houbak and Jeppesen (as
reported in Hansen [1991a]) concluded that kits weaned at 6 weeks of age were more
stressed than kits weaned later (the upper age is not given). Together with the findings of
Gimpel (1997), these results suggest that the mother continues to influence behavioural
development after nutritional independence, and that mink left with their mothers till 11
weeks of age will experience better welfare.
Hansen (1991a) examined kits weaned at 6, 8 and 12 weeks of age, and placed in pairs.
He found no difference between the groups in latency to intromission (a measure of
willingness to mate) and the number of successful matings. Despite the lack of an
individually housed control group, he concluded that the physical contact between the kits
placed in pairs in conventional cages was sufficient to secure normal reproductive behaviour,
Jonasen (1987, cited in Hansen [1991a]) found no difference in the ontogenesis of kits raised
under farm and semi-natural conditions.
220 Animal Welfare
1999,8:
205-228
The welfare of farmed mink
irrespective of weaning age. Using a small sample size (n
=
3 in each group), Gilbert and
Bailey (1969a) concluded that females weaned at 5-8 weeks of age were significantly easier
to mate than those weaned at 8-10 weeks, although male breeding performance seemed to
depend on a critical period of socialization from 5~8 weeks of age. However, the 1988
studies of Houbak and Jeppesen (cited in Hansen [199la]), and of de longe (1988; 1989),
Mason (1994; 1996), and Gimpel (1997) indicate that other aspects of normal behaviour, and
the long-term welfare of mink, are at risk from the standard weaning age adhered to on
farms.
Heller et al (1988) examined mother-kit separation from the mother's perspective, using
changes in circulating eosinophil levels as an indicator of welfare. They found that the
mother's levels increased with the weaning age of the kits from 6 to 8 to 10 weeks, with
levels significantly highest when kits were at 10 weeks of age. However, levels reduced
immediately following separation from the kits when they were 8 and 10 weeks of age,
whereas the mother showed a prolonged reaction to separation at 6 weeks of age. While it
seems likely that later weaning is better for the long-term welfare of kits, the short-term
consequences for mothers which have to live with grown kits for longer may be ameliorated
by the provision of a resting area which only mothers can access (see, Additions to the
standard cage environment, with regard to allowing females an escape from their kits). In
addition, work by de Jonge and van Iwaarden (1995) found that mothers which remained
living with their kits in a greatly increased cage area remained healthy.
Lack of knowledge of the effects of olfactory, auditory, visual stimuli
The biology of feral mink indicates that various olfactory, auditory and visual stimuli may
have significant effects on mink, although such effects may be unrecognized by humans. For
example, Dunstone (1993) has commented that given the mink's (likely) high dependence on
olfactory stimulation in detecting and even recognizing conspecifics, the overwhelming
aroma on farms might be a source of chronic irritation. Preliminary studies have suggested
that females in cages sprayed with the urine of the male prior to mating show no increase in
successful matings (Moller 1991b), but such a study hardly considered the welfare of mink
subjected to a concentrated mix of odours. The effects of the auditory environment are also
unknown. Photoperiod has been shown to substantially affect mink: but whereas Kavanau et
al (1973) examined light level preferences in other mustelids, no such work has been done
on mink. Newberry (1995) has emphasized the importance of examining the effects of the
wider environment on captive animals, ie of all stimuli within their sensory range. Few
conclusions can be drawn regarding the extent to which these factors may affect the welfare
of farmed mink.
Overall comments regarding research on the housing aspects of farmed mink welfare
This review has examined the available scientific evidence and has endeavoured to evaluate
the state of knowledge regarding farmed mink welfare. While it is encouraging that a recent
increase in research effort has attempted to examine the welfare of farmed mink, it is
extremely important that such research is of adequate quality and is readily available to the
wider scientific community. A proportion of the available literature has been published
without peer review and does not include sufficient detail to permit thorough analysis of the
work undertaken.
Animal Welfare 1999, 8: 205-228 221
Nimon and Broom
Conclusions and animal welfare implications
i) Feral mink which have escaped from farms have become established in Europe.
Extensive studies of such animals indicate that kits do not leave their natal territory
until 11 or 12 weeks of age, that climbing, swimming and diving are significant
aspects of their lifestyle, that they regularly engage in travelling and foraging over
distances of at least
1-3
km, that they make use of a number of different dens and
that they probably make extensive use of scent-marking and olfactory cues. All
these aspects of their natural behaviour are denied them on mink farms.
ii) Mink have been kept in captivity for relatively few generations. No research effort
has focused on long-term selective breeding of mink for reduced fear in relation to
farm conditions; and research which has been conducted has, thus far, indicated only
that mink can be bred to be more fearful over a few generations.
iii) The high level and pervasiveness of stereotypies among farmed mink, and the
incidence of fur chewing and even self-mutilation of tail tissue, suggest that farmed
mink welfare is not good. Stereotypies are associated with negative consequences
such as slower kit growth, and higher levels of feed intake without an increase in
growth.
iv) Research has been sufficient to show that farmed mink have poorer welfare when
they are denied access to a nest box. A nest box is clearly essential.
v) Lactating female mink, and kits in the first
5-6
weeks of life, seem to experience
problems with dehydration. The provision of water so as to avoid dehydration is
important.
vi) Merely increasing cage size, without a consequent increase in enrichment, does not
appear to improve welfare.
vii) Some experiments concerning enrichment of the standard cage environment suggest
that additions can improve the welfare of mink. Research in this area has not been
sufficiently far-reaching.
viii) Studies aimed at improving housing conditions for mink have, on the whole, been
conceived and conducted within the framework of the standard cage environment.
This has limited the aspects of mink housing welfare which have been subject to
scientific investigation. A small number of recent studies indicate that moving away
from a cage-housing system towards an enriched enclosure-type system may benefit
captive mink. Mink show very strong preferences for access to water in which they
can swim and also strong preferences for an alternative hay box (ie nest box) and for
novel objects. They will also use tunnels or branches for climbing, and will
manipulate objects if they are available. There has been no research in which
knowledge gained from studies of wild mink biology has been used to design and
test a complete, improved enclosure for farmed mink.
ix) Research concerning social interactions between mink suggests that housing in pairs
or larger groups of mink may not be detrimental. It may possibly provide
enrichment for animals. Socially housed mink must be familiar with one another,
having been housed together since weaning.
x) There is acceptable evidence that kits on mink farms are weaned too early. Such
mink may be deprived of an aspect of social development which could lead to them
becoming better-adjusted adults. Further large-scale studies should examine whether
leaving mink and kits together until the age of 11 or 12 weeks would improve the
mink's long-term behaviour on farms.
222 Animal Welfare
1999,8: 205-228
The welfare of farmed mink
xi) Much of the research in this area is not of an adequate scientific standard. Any
future efforts should aim to correct this problem.
xii) As summarized in conclusions ii), iii), v), viii) and x), there is considerable evidence
of poor welfare in mink kept in the most widely used cages and under normal
management procedures.
Acknowledgements
The authors wish to acknowledge financial support from Respect for Animals, and to thank
Georgia Mason and Jonathon Cooper for constructive discussion. Our thanks also to the
many authors who sent reprints.
References
Bildsoe M, Heller K E and Jeppesen L L 1990a Stereotypies in adult ranch mink. Scientifur 14: 169-177
Bildsoe M, Heller K E and Jeppesen L L 1990b Stereotypies in female ranch mink; seasonal and diurnal
variations. Scientifur 14: 243-247
Bildsoe M, Heller K E and Jeppesen L L 1991 Effects of immobility stress and food restriction on
stereotypies in low and high stereotyping female ranch mink. Behavioural Processes 25: 179-189
(Special Issue: Stress responses in domestic animals)
Birks
J
D Sand Dunstone N 1985 Sex-related differences in the diet of the mink Mustela vison. Holarctic
Ecology 8: 245-252
Birks
J
D S and Linn I
J
1982 Studies of home range of the feral mink, Mustela vison. Symposia of the
Zoological Society of London 49: 231-257
Braastad B
0
1992 Progress in the ethology of foxes and mink. Nonvegian Journal of Agricultural
Sciences (Suppl. 9): 487-504
Brinck C, Gerell Rand Odham G 1978 Anal pouch secretion in mink Mustela vison. Oikos 30: 68-75
Broom D M 1996 Animal welfare defined in terms of attempts to cope with the environment. Acta
Agriculturae Scandinavica Section A: Animal Science Supplement 27: 22-28
Broom D M and Johnson KG 1993 Stress and Animal Welfare. Chapman
&
Hall: London, UK
Bryant C E, Rupniak N M J and Iversen S D 1988 Effects of different environmental enrichment devices
on cage stereotypies and autoaggression in captive Cynomolgus monkeys. Journal of Medical
Primatology 17: 257~269
Burton R 1979 Carnivores of Europe. BT Batsford: London, UK
Clapperton K B, Minot E
0
and Crump D R 1988 An olfactory recognition system in the ferret Mustela
fura L. (Carnivora, Mustelidae). Animal Behaviour 36: 541-553
Cooper J J and Mason G J 1996 Environmental requirements in mink. In: Duncan I JH, Widowski T M
and Haley DB (eds) Proceedings of the 30th International Congress of the International Society for
Applied Ethology, Guelph. Ontario, 14-17 August p 37. The Colonel K L Campbell Centre for the Study
of Animal Welfare: Guelph, Canada
Cooper J J and Mason G J 1997a Income elasticity as an indicator of behavioural priorities in mink
(Mustela vison). In: Hemsworth P H, Spinka M and Kostal L (eds) Proceedings of the 31st International
Congress of the ISAE (International Society for Applied Ethology). Prague. Czech Republic.I 3-1 6
August P 64. Research Institute of Animal Production: Prague, Czech Republic
Cooper
J J
and Mason G
J
1997b The behavioural priorities of mink (Mustela vison) in a closed economy.
In: British Society of Animal Science Winter Meeting 1997 paper 17. BSAS:Penicuik, UK
Cooper J J and Mason G J 1997c The effect of cost of access on consumption of environmental resources
in mink. In: Forbes
J
M, Lawrence T
J
L, Rodway R G and Varley M A (eds) Animal Choices pp 129-
13. (Occasional Publication No 20). British Society of Animal Science: Edinburgh, UK
Cooper
J J,
Odberg F and Nicol C J 1996 Limitations on the effectiveness of environmental improvement
in reducing stereotypic behaviour in bank voles (Clethrionomys glareolus). Applied Animal Behaviour
Science 48: 237-248
Animal Welfare
1999,8:
205-228 223
Nimon and Broom
Damgaard B M and Hansen S W 1996 Stress, physiological status and fur properties in farmed mink
placed in pairs or singly. Acta Agriculturae Scandinavica Section A: Animal Science 46: 253-259
Day M G and Linn I J 1972 Notes on the food of feral mink Mustela vison in England and Wales. Journal
of Zoology, London 167: 463-473
Deaux E and Engstrom R 1973 The temperature of ingested water: its effect on body temperature.
Physiological Psychology 1: 152-154
de Jonge G 1988 Genetics and evolution of tail biting in mink. In: Murphy D M and Hunter DB (eds)
Biology, Pathology and Genetics of Fur-bearing Animals pp 503-505. (Unpublished Proceedings of the
IVth International Scientific Congress on Fur Animal Production, Toronto)
de Jonge G 1989 Genetics and evolution of tail-biting by mink. Fur Rancher 69: 5-6
de Jonge G 1996a De invloed van groepshuisvesting op groei en ·pelskwaliteit. De Pelsdierenhouder
(February): 49-54
de Jonge G 1996b Groephuisvesting doet kwaliteit geen kwaad. De Pelsdierenhouder (April): 124-125
de Jonge G and Carlstead K 1987 Abnormal behaviour in farm mink. Applied Animal Behaviour Science
17: 375
de Jonge G, Carlstead K and Wiepkema PR 1986 The Welfare of Ranch Mink.(COVP issue no 08). Het
Spelderholt Beekbergen, The Netherlands
de Jonge G and van Iwaarden M 1995 Een nieuw huisvestingssysteem voor nesten. De Pelsdierenhouder
(January): I~-24
DonCarlos M W, Petersen J S and Tilson R L 1986 Captive biology of an asocial Mustelid; Mustela
erminea. Zoo Biology 5(4): 363-370
Dunstone N 1983 Underwater hunting behaviour of the mink (Mustela vison Schreber): an analysis of
constraints on foraging. Acta Zoologici Fenneca 174: 201-203
Dunstone N 1993 The Mink. T
&
AD Poyser Ltd: London, UK
Dunstone N and Birks J D S 1983 Activity budget and habitat usage by coast-living mink (Mustela vison).
Acta Zoologici Fenneca 174: 189-191
Dunstone N and Birks J D S 1985 The comparative ecology of coastal, riverine and lacustrine mink
Mustela vison in Britain. Zeitschrift fur Angewandte Zoologie 72: 59-70
Dunstone N and Birks J D S 1987 The feeding ecology of mink (Mustela vison) in a coastal habitat.
Journal of Zoology, London 212: 69-83
Dunstone N and Sinclair W 1978a Comparative aerial and underwater visual acuity of the mink (Mustela
vison Schreber) as a function of discrimination distance and stimulus luminance. Animal Behaviour 26:
6-13
Dunstone N and Sinclair W 1978b Orienting behaviour during aerial and underwater visual discrimination
by the mink (Mustela vison Schreber). Animal Behaviour 26: 14-21
Elofson L, Lagerkvist G, Gustafsson H and Einarsson S 1989 Mating systems and reproduction in mink.
Acta Agriculturae Scandinavica 39: 23-41
Enders R K 1952 Reproduction in the mink (Mustela vison). Proceedings of the American Philosophical
Society 96: 691-755
Erlebach S 1993 Effects of environment on the behaviour of mink. In: Nichelmann M, Wierenga H K and
Baun S (eds) Proceedings of the International Congress on Applied Ethology, Berlin pp 108-112.
Humboldt University: Berlin, Germany
Erlebach S 1994 Effects of environment on the behaviour of mink. Applied Animal Behaviour Science 40:
77 (Abstract)
Foss I and Flottorp G 1974 A comparative study of the development of hearing and vision in various
species commonly used in experiments. Acta Otolaryngologica 77: 202-214
Fraser D 1975 The effect of straw on the behaviour of sows in tethered stalls. Animal Production 21: 59-68
Fraser A F and Broom D M 1990 Farm Animal Behaviour and Welfare, 3rd edition. Bailliere Tindall:
London, UK
Gerell R 1968 Food habits of mink, Mustela vison, in Sweden. Viltrevy 5: 119-211
224 Animal Welfare 1999, 8: 205-228
The welfare of farmed mink
Gerell R 1970 Home ranges and movements of mink (Mustela vison) in Sweden. Gikos 21:
160-173
Gilbert F F and Bailey E D 1967 The effect of visual isolation on reproduction in the female ranch mink.
Journal of Mammology 48: 113-118
Gilbert F F and Bailey E D 1969a The effect of early weaning on the sexual behaviour and reproductive
success of ranch mink. Journal ofMammology 50:
742-747
Gilbert F F and Bailey E D 1969b Visual isolation and stress in female ranch mink particularly during the
reproductive season. Canadian Journal of Zoology 47: 209-212
Gilbert FF and Bailey ED 1970 Reproductive performance of three genetic strains of female mink visually
isolated after breeding. Cornell Vet 60:
135-138
Gimpel J 1997 The role of the mother as a secure base in the development of exploration in young mink
(Mustela vison). Unpublished MSc thesis, University of Oxford, UK
Gulevich R G, Klochkov D, Ivanola L Nand Osadchuk L V 1995 Gonadal function in the mink under
artificial photoperiods. Journal of Reproduction and Fertility 103:
147-152
Hansen C P B 1993 Stereotypies in ranch mink: The effect of genes, litter size and neighbours. Behavioural
Processes 29: 165-177
Hansen S W 1988 Effect of variable cage size and lack of admission to nestbox on the behaviour,
physiology and production of mink kits. In: Murphy B D and Hunter DB (eds) Biology, Pathology and
Genetics of Fur-bearing Animals pp 153-162. (Unpublished Proceedings of the IVth International
Scientific Congress on Fur Animal Production, Toronto)
Hansen S W 1990 Activity pattern of lactating mink and the effect of water trays or wire netting cylinder in
mink cages. Scientifur 14: 187-193
Hansen S W 1991a Behaviour and environment of mink. In: Moller S (ed) Production of Mink, the
Influence of Various Management, Environmental and Nutritional Elements on Behaviour, Physiology
and Production in Mink pp. 63-96. Beretning fra Statens Husdyrbrugsforsog - 688. Ministry of
Agriculture, National Institute of Animal Science: Foulum, Denmark
Hansen S W 1991 b Selektion for adfaerdsnaessige kriterier hos farmmink. Bilag til Statens
Husdyrbrugsforsogs Arsmode (21-22 May): 17-18
Hansen S W 1996 Selection for behavioural traits in farm mink. Applied Animal Behaviour Science 49:
137-148
Hansen S Wand Brandt A 1989 Effect of cage size and nest box on the haematological/enzymological
status and physiological stress levels in mink kits. Scientifur 13: 185-192
Hansen S Wand Damgaard B M 1991 a Effect of environmental stress and immobilisation on stress
physiological variables in farmed mink. Behavioural Processes 25: 191-204
Hansen S Wand Damgaard B M 1991 b Stress, physiological, hematological, and clinical-chemical status
of farm mink placed in groups or singly. Acta Agriculturae Scandinavica 41: 355-366
Hansen S W, Hansen B K and Berg P 1994 The effect of cage environment and ad libitum feeding on the
circadian rhythm, behaviour and feed-intake of farm mink. Acta Agriculturae Scandinavica Section A:
Animal Science 44: 120-127
Hansen S W, Hansen B K and Damgaard B M 1992 The effects of cage environment on the welfare of
mink. Norwegian Journal of Agricultural Sciences (Suppl. 9): 536-544
Harlow H F and Zimmerman R R 1959 Affectional responses in the infant monkey. Science 130: 421-432
Harri M, Nurminen Land Filen T 1995 Stomach ulcer as an indicator of stress in farm mink. Acta
Agriculturae Scandinavica Section A: Animal Science 45: 204-207
Heller K E, Houbak B and Jeppesen L L 1988 Stress during mother-infant separation in ranch mink.
Behavioural Processes 17: 217-227
Heller K E and Jeppesen L L 1985 Behavioural and eosinophil leucocyte responses to single and repeated
immobility stress in mink. Scientifur 9: 174-178
Heller K E and Jeppesen L L 1986 Effects of social stress on circulating eosinophil leukocytes and sexual
behaviour in ranch mink. Scientifur 10:
167-170
Hinde R A 1970 Animal Behaviour, 2nd edition. McGraw-Hill: New York, USA
Animal Welfare 1999, 8: 205-228 225
Nimon and Broom
Houbak B 1990 Bestemmelse af socialrang hos farmmink. Bilag til Statens Husdryrbrugsforsogs, Arsmode
(15-16 May): 90-97
Jackson M K, Winslow S G, Dockery L D, Jones J K and Sisson D V 1996a Investigation of an outbreak
of Aleutian disease on a commercial mink ranch. American Journal of Veterinary Research 57: 1706-
1710
Jackson M K, Ellis L C, Morrey J D, Li Z Z and Barnard D L 1996b Progression of Aleutian disease in
natural and experimentally-induced infections of mink. American Journal of Veterinary Research 57:
1753-1758
Jallageas M, Boissin J and Mas N 1994 Differential photoperiodic control of seasonal variations in
pulsatile luteinizing hormone release in long-day (ferret) and short-day (mink) mammals. Journal of
Biological Rhythms 9: 217-23 I
Jeppesen L L, Bildsoe M and Helleer K E 1990 Production and abnormal behaviour. NJF Utredning
Rapport 60. National Institute of Animal Science: Foulum, Denmark
Jeppesen L L and Falkenberg H 1990 Effect of play balls on pelt biting, behaviour and stress levels in
ranch mink. Scientifur 14: 179-186
Joergensen G 1985 Mink Production. Scientifur: Hilleroed, Denmark
Jonasen B 1987 Ad faerdsfomg med burstorrelser til mink. Statens Husdyrbrugsfors0g 652. National
Institute of Animal Science: Foulum, Denmark
Kavanau L J, Ramos J and Havenhill R M 1973 Compulsory regime and control of environment in
animal behaviour: II. Light level preferences of carnivores. Behaviour 46: 279-299
K1otchkov D V, Gulevich R G, Osadchuk L V and Kim A A 1985 The photoperiodic programming of the
gonad's endocrine function and spermotogenesis in young mink. Journal of General Biology 46: 679-
685
Kollberg E and BjiSrkland B 1989 Sjukdomar och skador vidburuppfOdning av piilsdjar. Piilsdjursfakta.
Riidda Piilsdjuren, Nordisk Samfundeet mot Plagsamma DjurfOrsok
Markowitz H 1982 Behavioural Enrichment in the Zoo. Van Nostrand Reinhold: London, UK
Markowitz H, Aday C and Gavazzi A 1995 Effectiveness of acoustic prey: environmental enrichment for
a captive African leopard (Panthera pardus). Zoo Biology 14: 371-379
Marriner L M and Drickamer L C 1994 Factors influencing stereotyped behaviours of primates in a zoo.
Zoo Biology 13: 267-275
Martino P E, Martino J J and Villar J E 1991 A note on diseases of mink. Journal of Veterinary
Medicine, Series B, 38: 227-230
Mason G J 1991 a Individual differences in the stereotypies of caged mink. Unpublished PhD thesis,
University of Cambridge, UK
Mason G J 1991 b Stereotypies: a critical review. Animal Behaviour 4/:
1015-1037
Mason G J 1992 Stereotypy and welfare in mink. Journal of Animal Science (Suppl.) 70: 158
Mason G J 1993 Age and context affect the stereotypies of caged mink. Behaviour 127: 191-229
Mason G J 1994 Tail-biting in mink (Mustela vison) is influenced by age at removal from mother. Animal
Welfare 3: 305-311
Mason G J 1996 Early weaning enhances the later development of stereotypy in mink. In: Duncan I
J
H,
Widowski T M and Haley D B (eds) Proceedings of the 30th International Congress of the International
Society for Applied Ethology p 16. The Colonel K L Campbell Centre for the Study of Animal Welfare:
Guelph, Canada
Mason G J, Leipoldt A and de Jonge G 1995 Why do female mink with high stereotypy levels have slow-
growing offspring? In: Rutter S M, Rushen J, Randle H D and Eddison
J
C (eds) Proceedings of the
29th International Congress of the International Society for Applied Ethology, Exeter, UK,
3-5
August
pp 133-134. Universities Federation For Animal Welfare: Potters Bar, UK
Moller S 1990 The need for nest boxes and drop-in bottoms in the whelping period of the female mink.
Scientifur 14: 95-100
226 Animal Welfare 1999, 8: 205-228
The welfare of farmed mink
Moller S 1991 a Drinking behaviour of mink in relation to watering system and water temperature. NJF
Seminar No 192, Uppsala March 6-7 1991. Ministry of Agriculture, National Institute of Animal
Science: Foulum, Denmark
Moller S 1991b Management and environment in mink production. In: Moller S (ed) Production of Mink,
the Influence of Various Management, Environmental and Nutritional Elements on Behaviour,
Physiology and Production in Mink pp 13-62. Beretning fra Statens Husdyrbrugsforsog - 688.
Ministry of Agriculture, National Institute of Animal Science: Foulum, Denmark
Moller S 1991c Weight gain and hair chewing in mink kits placed singly or in pairs from September.
Scientifur 15: 21-27
Moller S ]992 Production systems and management in the Danish mink production. Norwegian Journal of
Agricultural Science (Suppl. 9): 562-568
Moller S and Hansen S W 1993 Weight development and behaviour of mink in the nursing period with
and without the use of spray watering. Scientifur 17: 107-114
Newberry R C 1995 Environmental enrichment: increasing the biological relevance of captive
environments. Applied Animal Behaviour Science 44: 229-243
Niemimaa J 1995 Activity patterns and home ranges of the American mink (Mustela vison) in the Finnish
Outer Archipelago. Annales Zoologici Fennici 32: 117-12]
Niemimaa J and Pokki J 1990 Minkin ravinnasta Suomenlahden ulkosaaristossa. Suoman Riista 36: 18-30
Odberg F
0
1987 The influence of cage size and environmental enrichment on the development of
stereotypies in bank voles (Clethrionomys glareolus). Behavioural Processes 14: 155- 173
Poole T Band Dunstone N 1976 Underwater predatory behaviour of the American mink (Mustela vison).
Journal of Zoology, London 178: 395-412
Rice R P 1967 The mink: a short outline of general management. Journal of the Institute of Animal
Technicians 18: 66-80
Rushen
J
and de Passille A M B 1992 The scientific assessment of the impact of housing on animal
welfare: a critical review. Canadian Journal of Animal Science 72: 721-743
Schneider R R and Hunter D B 1993a A survey of the causes of mortality in adult mink, with emphasis on
the lactation period. Canadian Veterinary Journal 34: 103-108
Schneider R R and Hunter D B 1993b Nursing disease in mink: clinical and postmortem findings.
Veterinary Pathology 30: 512-521
Schneider R R, Hunter D Band Waltnertoews D 1992 Nursing disease in mink: ranch level
epidemiology. Preventive Veterinary Medicine 14: ]8] -194
Shackelford R M 1950 Genetics of the Ranch Mink. Pillsbury Pub Inc: New York, USA
Shackelford R M 1984 American mink. In: Mason I L (ed) Evolution of Domesticated Animals pp 229-
234. Longman: London, UK
Shepherdson D J, Carlstead K, Mellen J D and Seiden sticker J 1993 The influence of food presentation
on the behaviour of small cats in confined environments. Zoo Biology 12: 203-216
Sinclair W, Dunstone N and Poole T B 1974 Aerial and underwater visual acuity in the mink (Mustela
vison Schreber). Animal Behaviour 22: 965-974
Skovgaard K, Jeppesen L L and Hansen C P B 1997 Would you like a swim, madam mink? Scientifur
24: 247-251
Sonderup M 1990 Bidekopper og bolde kan reducere pelsgnav. Dansk Pelsdyravl 53: 396-398
Stevens R T, Ashwood T L and Sleeman
J
M 1997 Fall early winter home ranges, movements, and den
use of male mink, Mustela vison, in eastern Tennessee. Canadian Field Naturalist 111: 312-314
Valtonen M, Vakkuri
0
and Blomstedt L 1995 Autumnal timing of photoperiodic manipulation critical
via melatonin to winter pelage development in mink. Animal Science 61: 589-596
Vestergaard K 1983 Behaviour and Reproduction in Optically Isolated Female Mink. (Unpublished
abstract, Society for Veterinary Ethology Meeting [1983], Tours, France)
Wahlstrilm K 1987 Orsakeer till dodlighet hos mink. Vara Palsdjar 58: 297-310
Animal Welfare
1999,8:
205-228 227
Nimon and Broom
Zielinski W J ]986 Circadian rhythms of small carnivores and the effect of restricted feeding on daily
activity. Physiology
&
Behavior 38: 613-620
Zielinski W J ]988 The influence of daily variation in foraging cost on the activity of small carnivores.
Animal Behaviour 36: 239-249
228 Animal Welfare 1999,
8:
205-228
... Wild animals will hide in dens, burrows, or other naturally secluded areas at times other than parturition. For example, predators such as wild red foxes [22] and American mink [23] reside in dens, which often take the form of natural hollows in the earth or repurposed rabbit dens. These dens are typically situated under trees or other areas on natural cover as to act as shelter and protection from higher predators [22,24], and the animals often move frequently between several different dens [23]. ...
... For example, predators such as wild red foxes [22] and American mink [23] reside in dens, which often take the form of natural hollows in the earth or repurposed rabbit dens. These dens are typically situated under trees or other areas on natural cover as to act as shelter and protection from higher predators [22,24], and the animals often move frequently between several different dens [23]. Similarly, prey species such as rabbits live in dens much like mink and foxes, although the rabbit typically builds the den themselves [25]. ...
... Fur carnivores, including farmed foxes and mink, were the next most represented animal type in this category of papers (18/65). Farmed foxes and mink are unique, as it is often considered standard for modern farming to provide these animals with hiding boxes in the cage [23]. Thus, the papers found for this review primarily focus on the impact of giving foxes and mink additional hiding places, often in combination with other enrichment items. ...
Article
Full-text available
Many wild animals perform hiding behaviours for a variety of reasons, such as evading predators or other conspecifics. Unlike their wild counterparts, farmed animals often live in relatively barren environments without the opportunity to hide. Researchers have begun to study the impact of access to hiding spaces (“hides”) in farmed animals, including possible effects on animal welfare. The aims of this scoping review were to: 1) identify the farmed species that have been most used in research investigating the provision of hides, 2) describe the context in which hides have been provided to farmed animals, and 3) describe the impact (positive, negative or neutral/inconclusive) that hides have on animals, including indicators of animal welfare. Three online databases (CAB Abstracts, Web of Science, and PubMed) were used to search for a target population of farmed animals with access to hiding spaces. From this search, 4,631 citations were screened and 151 were included in the review. Fourteen animal types were represented, most commonly chickens (48% of papers), cattle (9%), foxes (8%), and fish (7%). Relatively few papers were found on other species including deer, quail, ducks, lobsters, turkeys, and goats. Hides were used in four contexts: at parturition or oviposition (56%), for general enrichment (43%), for neonatal animals (4%), or for sick or injured animals (1%). A total of 218 outcomes relevant to our objectives were found including 7 categories: hide use, motivation, and/or preference (47% of outcomes), behavioural indicators of affective state (17%), health, injuries, and/or production (16%), agonistic behaviour (8%), abnormal repetitive behaviours (6%), physiological indicators of stress (5%), and affiliative behaviours (1%). Hiding places resulted in 162 positive (74%), 14 negative (6%), and 42 neutral/inconclusive (19%) outcomes. Hides had a generally positive impact on the animals included in this review; more research is encouraged for under-represented species.
... Czynniki wywołujące zachowania kompulsywne u zwierząt futerkowych Zwierzęta futerkowe należą do grupy zwierząt gospodarskich, jednak pomimo wieloletniej hodowli wciąż trwają dyskusje, czy proces ich udomowienia został już zakończony (10,40). Nadal wśród norek, szynszyli czy lisów utrzymywanych na fermach można spotkać osobniki nieufne w stosunku do człowieka, lękliwe, a nawet agresywne. ...
Article
Fur animals kept indoors, due to partial limitation of their natural behavior, are more likely to develop behavioral disorders. This is due to negative emotions associated with inability to satisfy certain needs or achieve a particular purpose, which leads to frustration or deprivation in animals. This condition can lead to the emergence of compulsive behaviors, which are often a form of coping with stress. Compulsive behaviors in fur animals are usually stereotypical: animals walk along the cage, catch their own tail, gnaw fur (trichotilomanie), or bite the trellis or the claws. The environmental factors resulting from the maintenance conditions and social relations of the animals in the group play an important role in the emergence of this type of behavior. Another factor that is equally important in causing compulsive behavior is mental strain resulting from disease..
... It first should be understood that there is no consensus in animal welfare science on the ethics or desirability of keeping of fur animals. The two sides of the argument for farming mink have been discussed by Vinke (2001) and Nimon and Broom (1999), and foxes by Nimon and Broom (2001). Neither of course is there any consensus on the ethics of keeping of any groups of animals by humans. ...
Article
Full-text available
The discussion of the ethics of fur farming is currently important in Estonia, where the Estonian Parliament is due to make a judgement on the legality of farming animals for fur in the state. Although there is significant opposition among the local general population, and discussion in the popular and social media, there is little evidence of a coherent ethical reason why fur animals should not be farmed while we continue to permit the farming of other livestock animals. Ethical viewpoints of the rights and welfare of animals are presented here and these are contextualised with regard to fur farming and fur farming in Estonia in particular.
... food deprivation in the winter (see e.g. Bildsøe et al., 1990Bildsøe et al., , 1991 Mason, 1991; Nimon and Broom, 1999). None of the available papers addressed the feeding regimes in detail, and it can still be questioned how food regimes may influence stereotypies during the winter. ...
Article
This paper discusses the ethical implications of applying the concept of behavioural needs to captive animals. This is done on the basis of analysing the scientific literature on farmed mink and their possible need for swimming. In the wild, American mink (Mustela vison) are semi-Aquatic predators, lending initial support to the claim that captive mink with no access to adequate swimming facilities experience a thwarted behavioural need. Scientific studies show a disparate picture. Consumer-demand experiments, where the animals have been conditioned to work for environmental resources, consistently show that mink place high value on swimming water, whereas other studies indicate the opposite, which has led scientists to question whether this preference constitutes a genuine behavioural need. In this paper, we take a methodological turn and discuss whether the oft-used concept of behavioural needs provides the best possible account of what is indispensable to an animal. Seen from a more complex understanding of behavioural needs, we suggest that lack of swimming opportunities for farmed mink constitutes a welfare problem. Further, it is argued that the decision of which paradigm to use in research on animal needs has not only ethical consequences, but is in itself a value-based choice.
Article
The aim of this study was to investigate the activity patterns of American mink (Neovison vison). Twenty mink from a commercial mink farm were housed in a free-range enclosure (290 m²) at the age of 13 weeks. In the enclosure, the mink were offered 20 nest boxes (animal-to-nest-box ratio: 1:1), food ad libitum and 3 kinds of water basins. The activity rhythms and the use of the nest boxes were assessed by an automatic registration device that recorded the amount of time spent inside or outside the nest box or in the entrance tunnel for each individual mink over a time period of 18 weeks between July and December. In addition to analyzing the mink’s daily and seasonal activity patterns, we sought to detect any social preferences or preferences for individual nest boxes. Results showed that the mink had crepuscular activity patterns with 2 activity peaks during dusk and dawn, and that the former shifted when the daylight period shortened. Throughout the experiment, the activity time spent outside the nest boxes declined with increasing age and decreasing ambient temperature. In addition, the mink showed a preference for nest boxes that faced the feeding lots and not the water basins. During sleep and rest periods, the mink spent high amounts of time using the nest boxes in company. Furthermore, the mink structured their own habitat by using certain nest boxes for sleeping and others as latrine boxes. Small differences between male and female mink existed in their activity (i.e., time spent inside or outside nest boxes) but not in their preference for certain nest boxes or other individuals. Based on our results, any environmental enrichment item should be presented all day long, so each mink has the opportunity to use them individually during their main activity times mostly at dusk and dawn and their daily handling should be adjusted to this rhythm. A mink-to-nest-box ratio of 1:1 does not seem necessary, as juvenile mink often slept in groups of 2 or more animals in 1 nest box. Furthermore, the animals should be given the opportunity to distinguish between a sleeping and a latrine area.
Article
Full-text available
Animal welfare is one of the most important elements of modern of livestock rearing. Ensuring adequate living conditions that meet basic biological needs of animals is key to the success of breeding. The occurrence of stress behaviors on fur farms is associated with an unfinished process of domestication of these animals. The use of environmental enrichments allows the manifestation of natural behavior of these animals as well as reduces the occurrence of stereotyped behavior or biting the fur. The use of toys or other enrichments reduces the occurrence of apathy, depression, which results from the limited living conditions. Behavior manifested by animals is also an important factor in animal husbandry. In order to assess the emotional state of animals may be used behavioral tests. The most popular tests used in farm fur animals include: empathetic test, glove test, feeding test.
Article
Full-text available
Abnormal behaviour is a potential indicator of pain, suffering and injury in captive animals. Especially stereotypies, i.e. repetitive invariant behavioural patterns without obvious function or goal, can be observed as a consequence of inadequate housing conditions. Hence, they are often considered indicators of impaired welfare. In context of the ongoing scientific debate on captive animal welfare, the number of publications on stereotypies has increased, most notably in veterinary and farm animal research. Based on biological principles and definitions, we present several examples of stereotypic behaviour in (mainly) farm animals, and discuss approaches of preventing or reducing them. The occurrence of abnormal behaviour is often, but not necessarily, associated with the fact that modern housing and management precludes various evolutionary emerged highly motivated behaviours, or poses challenges the animals are unable to cope with adequately. Numerous studies show that stereotypies can be indicative of (current or past) suffering and impaired welfare. They can be avoided or at least reduced by increasing the biological relevance of the housing environments through environmental enrichment which stimulates species specific behaviour.
Article
Humans have a natural interest in animals; through a long history of domestication, they have become tools, a food source and even friends. Behaviour is a significant indicator of animal health and well-being, and understanding this behaviour is therefore the key to good management. Covering all aspects of animal behaviour and how this relates to welfare for companion animals, farm animals and farmed fish, this book reviews development, socialisation, locomotion, reproduction and more. It takes a comprehensive approach to the subject, including a section of chapters addressing common abnormal behaviours and reviewing some animals, such as rabbits, from both a pet and farm perspective. Now in its fifth edition, Domestic Animal Behaviour and Welfare includes new chapters detailing the welfare of sheep, goats and exotic pets, and welfare in relation to genetic selection and modification. Animal behaviour and welfare sciences are now core topics for agriculture and veterinary students, with courses and research opportunities in this field growing world-wide. Fully updated and with new photographs, this indispensable textbook provides a student-friendly guide to the major themes of animal behaviour and welfare.
Article
Captive/domestic animals are often described as inactive, with the implicit or explicit implication that this high level of inactivity is a welfare problem. Conversely, not being inactive enough may also indicate or cause poor welfare. In humans, too much inactivity can certainly be associated with either negative or positive affective states. In non-human animals, however, the affective states associated with elevated or suppressed levels of inactivity are still not well understood.Part of the complexity is due to the fact that there are many different forms of inactivity, each likely associated with very different affective states. This paper has two aims. One is to identify specific forms of inactivity that can be used as indicators of specific affective states in animals. The other is to identify issues that need to be resolved before we could validly use the remaining, not yet validated forms of inactivity as indicators of affective state.We briefly discuss how inactivity is defined and assessed in the literature, and then how inactivity in its various forms relates to affective (either negative or positive) states in animals, basing our reasoning on linguistic reports of affective states collected from humans displaying inactivity phenotypically similar to that displayed by animals in similar situations, and, when possible, on pharmacological validation. Specific forms of inactivity expressed in response to perceived threats (freezing, tonic immobility, and hiding) appear to be, to date, the best-validated indicators of specific affective states in animals. We also identify a number of specific forms of inactivity likely to reflect either negative (associated with ill-heath, boredom-like, and depression-like conditions), or positive states (e.g. 'sun-basking', post-consummatory inactivity), although further research is warranted before we could use those forms as indicators of the affective states. We further discuss the relationship between increased inactivity and affective states by presenting misleading situations likely to yield wrong conclusions. We conclude that more attention should be paid to inactivity in animal welfare studies: specific forms of inactivity identified in this paper are, or have the potential to be, useful indicators of affective (welfare) states in animals.
Book
Full-text available
This is a book. The Preface describing contents is uploaded.
Article
Consumer demand theory has been used to assess the environmental requirements of domestic animals, because they will defend consumption of important resources, but not consumption of less important resources as their cost is increased (Dawkins, 1983). A commonly used approach is to place the cost on access to the resource, where once the animal has overcome the cost of access, there is no limit on time spent with a resource. So animals can compensate for fewer visits by spending longer with the resource on each visit (Sherwin and Nicol, 1995, Cooper and Mason, in press), in which case price paid and amount consumed may not covary, which would contravene the assumptions underlying the construction of demand functions (Mason et al., in press). In this experiment we investigated one solution to this problem: increasing the entry fee until the subject ceases to gain access to each resource.