Group housing in row cages: an alternative housing system for juvenile mink


Hänninen, S.; Ahola, L.; Pyykönen, T.; Korhonen, H.T.; Mononen, J.

Animal 2(12): 1809-1817

2008


We studied a group housing system as an alternative to the traditional pair housing of juvenile mink. The focus was on both the welfare and production of mink. The pairs were housed in standard mink cages, whereas the groups were in row cage systems consisting of three standard mink cages connected to each other. The welfare of the mink was evaluated by behavioural observations (stereotypies and social contacts), evaluation of the incidence of scars assumed to be caused by biting, and adrenal function (serum cortisol level after adrenocorticotropic hormone (ACTH) administration and adrenal mass). Feed consumption, pelt length, quality and price were used for comparing the two housing systems from the economic point of view. Although the incidence of scars showed that there might have been more aggressive behaviour among the group-housed than among the pair-housed mink, this was not observed unambiguously in behavioural observations, and, at least, aggression did not cause mortality or serious injuries to the animals as has been observed in some earlier studies. In addition, the housing system did not affect pelt size, and, although the quality of the pelts was slightly lower in the group than in pair-housed mink, there was only a tendency for lower pelt prices. The lower pelt prices in the group-housed mink might even be partially compensated for by the group-housed mink eating 10% to 20% less in the late autumn, due to thermoregulatory benefits, than their pair-housed conspecifics. The results on the frequency of stereotypic behaviour (but not adrenal function) suggest that the group-housed animals were possibly less stressed than the pair-housed animals. Group housing of juvenile farmed mink in a row cage system cannot be recommended before the effects on welfare and production are clarified in further studies.

Animal
(2008),
2:12,
pp
1809-1817
©
The
Animal
Consortium
2008
doi:10.1017/S175173110800311X
1!
)
)animal
Group
housing
in
row
cages:
an
alternative
housing
system
for
juvenile
mink
S.
Hanninen
it
,
L.
Ahola
l
,
T.
Pyykonen
1
,
H.
T.
Korhonen
2
and
J.
Mononen
1
'Department
of
Biosciences,
University
of
Kuopio,
PO
Box
1627,
FIN
-70211
Kuopio,
2
Agrifood
Research
Finland,
Animal
Production
Research,
PO
Box
44,
FIN
-69101
Kannus,
Finland
(Received
25
March
2008;
Accepted
28
July
2008;
First
published
online
2
September
2008)
We
studied
a
group
housing
system
as
an
alternative
to
the
traditional
pair
housing
of
juvenile
mink.
The
focus
was
on
both
the
welfare
and
production
of
mink.
The
pairs
were
housed
in
standard
mink
cages,
whereas
the
groups
were
in
row
cage
systems
consisting
of
three
standard
mink
cages
connected
to
each
other.
The
welfare
of
the
mink
was
evaluated
by
behavioural
observations
(stereotypies
and
social
contacts),
evaluation
of
the
incidence
of
scars
assumed
to
be
caused
by
biting,
and
adrenal
function
(serum
cortisol
level
after
adrenocorticotropic
hormone
(ACTH)
administration
and
adrenal
mass).
Feed
consumption,
pelt
length,
quality
and
price
were
used
for
comparing
the
two
housing
systems
from
the
economic
point
of
view.
Although
the
incidence
of
scars
showed
that
there
might
have
been
more
aggressive
behaviour
among
the
group
-housed
than
among
the
pair
-housed
mink,
this
was
not
observed unambiguously
in
behavioural
observations,
and,
at
least,
aggression
did
not
cause
mortality
or
serious
injuries
to
the
animals
as
has
been
observed
in
some
earlier
studies.
In
addition,
the
housing
system
did
not
affect
pelt
size,
and,
although
the
quality
of
the
pelts
was
slightly
lower
in
the
group
than
in
pair
-housed
mink,
there
was
only
a
tendency
for
lower
pelt
prices.
The
lower
pelt
prices
in
the
group
-housed
mink
might
even
be
partially
compensated
for
by
the
group
-housed
mink
eating
10%
to
20%
less
in
the
late
autumn,
due
to
thermoregulatory
benefits,
than
their
pair
-housed
conspecifics.
The
results
on
the
frequency
of
stereotypic
behaviour
(but
not
adrenal
function)
suggest
that
the
group
-housed
animals
were
possibly
less
stressed
than
the
pair
-housed
animals.
Group
housing
of
juvenile
farmed
mink
in
a
row
cage
system
cannot
be
recommended
before
the
effects
on
welfare
and
production
are
clarified
in
further
studies.
Keywords:
fur
farming,
fur
quality,
group
housing,
mink,
welfare
Introduction
The
worldwide
production
of
farmed
mink
(Neovison
vison,
earlier
Mustela
vison)
is
over
50
million
pelts
per
year
(Finnish
Fur
Breeders'
Association,
2008).
Most
farmed
mink
are
juveniles
born
in
the
spring
and
pelted
in
the
early
winter.
The
whole
population
of
mink
kept
on
farms
is
much
larger,
more
than
60
million
if
breeding
animals
and
indi-
viduals
that
die
before
pelting
are
included.
Thus,
any
improvements
in
the
housing
of
the
mink
would
affect
the
welfare
of
a
great
number
of
animals.
Traditionally,
the
juvenile
mink
are
raised
from
weaning
(at
the
age
of
6
to
8
weeks)
onwards
in
pairs,
in
cages
where
the
only
enrichments
are
another
mink
and
a
nest
box
with
wood
shavings
or
straw
as
bedding
material
(European
Commission,
2001).
Juvenile
mink
may
also
be
housed
singly
(Nimon
and
Broom,
1999).
However,
pair
-housed
mink
grow
better
(Moller,
t
E-mail:
sari.hanninen@uku.fi
1991)
and
show
fewer
and
later
developing
stereotypies
(Damgaard
and
Hansen,
1996)
than
singly
housed
mink
and
therefore
pair
housing
has
been
considered
to
be
better
for
the
mink.
Despite
these
benefits,
the
traditional
pair
housing
is
not
necessarily
the
optimal
way
of
housing
mink.
Even
the
pair
housing
system
has
been
considered
to
be
rather
barren,
and
it
has
been
argued
that
additional
enrichments
should
be
offered
to
the
mink
to
improve
the
welfare
of
these
animals
(Nimon
and
Broom,
1999).
Housing
in
larger
cage
systems
in
groups
of
more
than
two
animals
could
be
one
way
of
enriching
the
cage
environment
of
mink.
A
larger
cage
system,
required
for
a
group
of
animals,
makes
it
possible
for
all
the
animals
in
the
group
to
utilise
the
larger
space,
and
also
provides
room
for
a
more
complex
environment,
e.g.
tunnels,
removable
walls,
possibility
for
climbing
and
other
enriching
objects
(as
suggested
in
the
recommendations
of
the
European
Con-
vention
(1999)
and
the
report
of
the
European
Commission
(2001)).
Furthermore,
when
there
are
several
animals
in
the
1809
Hanninen,
Ahola,
Pyykonen,
Korhonen
and
Mononen
same
cage
system,
different
social
contacts
could
also
act
as
enrichment.
Although
mink
are
regarded
as
solitary
in
the
wild
(Birks,
1986;
Dunstone,
1993;
Niemimaa
and
Pokki,
1997),
juvenile
mink
have
been
raised
successfully
on
farms
in
pairs
or
triplets
for
decades
(Joergensen
1985).
Group
housing
of
mink
has,
in
principle,
been
enabled
by
both
European
recommendations
(European
Convention,
1999)
and
Finnish
National
Legislation
(Ministry
of
Agriculture
and
Forestry,
1999).
The
recommendations
of
the
European
Convention
(1999)
state
that
the
area
of
a
cage
of
a
mink
pair
must
be
at
least
2550
cm
2
,
and
each
additional
animal
must
have
at
least
850
cm
2
additional
space.
These
space
allowance
recommendations
are
embodied
in
Finnish
law
as
the
animal
welfare
requirements
for fur
animals
that
will
come
into
force
in
2010
(Ministry
of
Agriculture
and
Forestry,
1999).
However,
group
housing
should
not
be
implemented
before
more
experience
of
group
housing
at
a
research
scale
is
gained.
Scientific
studies
of
group
housing
of
mink
are
scanty
and
the
results
are
not
unambiguous.
In
some
studies,
the
experiences
are
mainly
promising
with
regard
to
production,
and
there
have
not
been
any
major
welfare
problems
(Jonge
de,
1996;
Vinke
et
al.,
2002).
In
other
studies,
mortality
has
been
higher
(Pedersen,
1999;
Pedersen
et
al.,
2004),
aggressive
behaviour
more
frequent
(Hansen
et
al.,
1997;
Pedersen,
1999;
Pedersen
et
al.,
2004;
Hanninen
et
al,
2008)
and
body
mass
at
pelting
lower
(Pedersen,
1999;
Lindberg
et
al.,
2005)
in
group
-housed
than
in
pair
-housed
mink.
On
the
other
hand,
group
-housed
mink
may
have
lower
adrenal
mass,
serum
cortisol
level
(Hanninen
et
al.,
2008)
and
urine
cortisol—creatinine
ratio
(Arts
et
al.,
2004),
less
tail
biting
(Jonge
de,
1996;
Pedersen,
1999;
Pedersen
et
al,
2004;
Hansen
and
Houbak,
2005)
and
less
stereotypies
(Jeppesen
et
al.,
2000)
than
pair
-housed
mink.
In
this
study,
we
compared
a
group
housing
system
and
the
traditional
pair
housing
of
juvenile
mink.
The
focus
was
on
both
the
welfare
and
production
of
mink.
The
pairs
were
housed
in
standard
mink
cages
and
the
groups
in
row
cage
systems
consisting
of
three
standard
mink
cages
connected
to
each
other.
The
welfare
of
the
mink
was
evaluated
by
behavioural
observations
(stereotypies
and
social
contacts),
incidence
of
scars
in
the
fleshed
skins
assumed
to
be
caused
by
biting,
and
adrenal
function
(serum
cortisol
level
after
adrenocorticotropic
hormone
(ACTH)
administration
and
adrenal
mass).
Feed
consumption,
pelt
size,
quality
and
price
were
used
for
comparing
the
two
housing
systems
from
the
economic
point
of
view.
Material
and
methods
Ethical
note
The
experiment
was
approved
by
the
Institutional
Animal
Care
and
Use
Committee
of
the
University
of
Kuopio
(Licence
nos.
00-32
and
02-39).
Animals
and
housing
conditions
The
experiment
was
carried
out
at
the
Juankoski
Research
Station
of
the
University
of
Kuopio.
Data
were
collected
during
2
years
with
similar
experimental
set-ups
in
both
years.
The
study
was
carried
out
in
an
unheated
animal
barn
with
eight
rows
of
mink
cages.
In
May,
the
wild
colour
-type
mink
dams
gave
birth
in
standard
mink
cages
with
a
wooden
nest
box
(Figure
1)
with
straw
as
bedding.
The
nest
box
was
situated
in
the
front
of
the
cage,
i.e.
nearest
to
the
corridor
between
the
cage
rows.
Twelve
(the
first
year)
and
14
(the
second
year)
litters
were
selected
for
the
study
from
the
whole
mink
population
of
the
farm
(61
and
55
litters,
respectively).
The
kits
were
weaned
from
their
mothers
at
the
age
of
8
weeks.
Three
male
and
three
female
kits
were
randomly
selected
from
each
litter
for
the
study,
and
extra
kits
were
removed
from
the
litters.
Matched
litter
pairs
were
formed,
by
taking
into
account
litter
size
and
age
of
the
kits,
and
were
divided
evenly
into
group
-housed
(GH,
n=
6
and
7
litters)
and
pair
-housed
(PH,
n
=
6
and
7
litters)
groups.
There
were
a
total
of
156
kits
(39
GH
males,
39
GH
females,
39
PH
males
and
39
PH
females)
in
the
experiment.
The
kits
were
marked
with
subcutaneous
microchips
(Indexel,
Digital
Angel
Corporation,
USA)
to
enable
identi-
fication
of
the
GH
individuals.
The
GH
mink
were
moved
as
litters
to
row
cage
systems
formed
by
connecting
three
standard
mink
cages
(with
nest
boxes),
and
the
mink
had
access
to
all
three
nest
boxes
(Figure
1).
The
PH
litters
were
housed
in
the
traditional
way,
i.e.
in
brother
—sister
pairs
in
standard
mink
cages
with
a
nest
box.
The
GH
and
PH
animals
were
placed
in
adjacent
cages
in
two
rows
so
that
each
PH
litter
had
its
matched
GH
litter
on
the
other
side
of
the
corridor
separating
the
two
cage
rows,
and
on
each
cage
row,
there
was
always
a
GH
litter
after
a
PH
litter.
Nest
boxes
with
straw
bedding
were
available
in
the
cages
of
both
groups
throughout
the
study.
The
animals
were
fed
ad
libitum
with
fresh
fur
-animal
feed
twice
a
day
until
the
end
of
September
and
once
a
day
thereafter.
The
feed,
containing
fish,
slaughter
offal,
grain,
protein
mixture,
oils,
water
and
vitamin
-iron
supplements,
was
manu-
factured
according
to
the
Finnish
recommendations
(Tuori
et
al.,
2000).
The
porridge
-like
feed
was
delivered
on
the
roofs
of
the
cages.
In
the
GH
group,
the
daily
feed
portion
was
divided
evenly
on
the
roofs
of
all
the
cages
of
each
litter.
Water
was
available
in
all
cages
ad
libitum
until
it
froze
in
November
and
thereafter
it
was
served
twice
a
day.
The
general
health
of
the
animals
was
checked
daily.
Data
collection
The
behaviour
of
the
animals
was
analysed
from
24-h
video
-
recordings
made
in
August,
i.e.
during
the
dispersal
time
of
mink
in
the
wild
(Niemimaa
and
Pokki,
1997),
and
in
November.
The
data
were
recorded
using
a
video
switcher
(switching
interval
50
s).
The
use
of
the
nest
boxes
('in
the
nest
box',
i.e.
the
animals
that
were
not
on
the
cage
floor
or
platform)
and
the
general
activity
in
the
cage
('active
in
the
cage',
'passive
in
the
cage')
were
analysed
from
the
video-
tapes
with
instantaneous
sampling
(Martin
and
Bateson,
1993)
with
3.5
to
4
min
intervals
(depending
on
the
number
of
cameras
in
use).
An
animal
was
regarded
as
passive
if
it
was
lying
down;
other
behaviours
were
regarded
as
active
beha-
viour.
If
it
was
not
possible
to
ascertain
(because
of
darkness
1810
Group
housing
of
juvenile
farmed
mink
A
E
R•
gl
N
Platform
23
cm
above
cage
floor
Plastic
tube
L
10
cm,
10
cm
0
CO
A
r
Gag
-
21:
-
10(
30
cm
Cage
height
38
cm
—1111—
1.11
.
Nest
box
height
30
cm
1
Corridor
Width
at
least
100
cm
s
for
one
PH
itter
0
cm
2
/cage
5
cm
2
/mink
L
Cage
system
for
one
GH
litter
-
6390
cm
2
/cage
system
-
1065
cm
2
/mink
Figure
1
Schematic
drawing
of
the
expe
imental
cages
from
above.
PH:
juvenile
mink
housed
in
male
—female
pairs
(three
from
each
litter)
in
standard
mink
cages,
GH:
juvenile
mink
housed
in
groups
of
three
males
and
three
females
(all
from
the
same
litter)
in
row
cage
systems.
Note
that
the
corridor
width
is
not
to
scale.
or
other
reasons
affecting
visibility
on
the
videotape)
whether
an
animal
was
in
the
cage
or
in
the
nest
box,
its
behaviour
was
classified
as
'not
known'.
Individual
animals
could
not
be
identified
from
the
videotapes
and
therefore
the
behavioural
analyses
were
done
within
litters,
i.e.
as
the
percentage
of
animals
within
each
litter
performing
a
certain
behaviour
at
a
sample
point.
The
analyses
were
done
within
litters,
i.e.
for
the
six
siblings
also
in
the
pair
-housed
animals,
to
obtain
data
that
were
comparable
between
the
groups.
Social
interactions
(including
fights,
threatening
or
biting
another
animal
and
social
play)
and
stereotyped
pacing
in
the
cage
were
analysed
with
one
—zero
sampling
(Martin
and
Bateson,
1993)
for
50
s
periods
with
3.5
to
4
min
intervals.
Social
interactions
and
stereotyped
pacing
were
pooled
within
each
litter,
i.e.
if
one
animal
was
performing
a
certain
behaviour,
that
behaviour
was
recorded
for
the
whole
litter.
The
dirtiness
of
the
nest
boxes
and
straw
bedding
in
the
box
was
scored
every
second
week
from
August
to
November
on
a
subjective
five
-point
scale
from
zero
(clean)
to
four
(extremely
dirty).
The
nest
boxes
were
manually
cleaned,
dirty
or
wet
bedding
was
removed
and
clean
bedding
added
after
every
scoring.
The
feed
consumption
of
the
litters
was
measured
in
September
and
again
in
November.
The
daily
ad
libitum
portions
and
leftovers
were
weighed
(accuracy
±1
g)
during
a
two-
(second
year)
or
three-
(first
year)
day
period.
The
results
were
combined
from
these
days
and
converted
to
daily
feed
consumption
per
animal
for
each
litter
(GH
or
PH)
per
day.
The
kits
were
weighed
(accuracy
±
1
g)
in
July
(at
weaning,
when
they
were
8
weeks
old),
August,
September,
October
and
November
(at
pelting,
when
the
kits
were
30
to
32
weeks
old).
At
pelting,
the
kits
were
injected
(i.m.)
with
0.06
ml
synthetic
ACTH
(Synacthen-Depot
1
mg/ml,
Ciba).
This
was
an
overdose
(at
least
0.023
mg/kg
°15
)
and
ensured
the
maximal
secretion
of
cortisol
to
blood
(for
the
ACTH
test,
see
e.g.
Broom
and
Johnson,
1993;
Terlouw
et
al,
1997).
Two
hours
later,
the
mink
were
humanely
killed
with
electrocution
accord-
ing
to
the
recommendations
of
the
European
Convention
(1999).
Death
was
ensured
by
immediate
neck
dislocation
after
electrocution.
Blood
samples
were
drawn
with
heart
puncture
immediately
after
death.
Serum
was
separated
and
stored
at
+4°C
and
analysed
for
cortisol
(Coat
-A
-Count
Cortisol
Assay
by
Diagnostic
Products
Corporation,
Los
Angeles,
CA,
USA)
within
1
week.
The
animals
were
pelted,
and
the
carcasses
were
autopsied
to
measure
the
adrenal
masses
(accuracy
±
0.1
mg)
as
a
second
indicator
of
adrenal
function
(Selye,
1950;
Gomez
et
al.,
1996;
Hemsworth
et
al.,
1996).
1811
Hanninen,
Ahola,
Pyykonen,
Korhonen
and
Mononen
The
pelted
skins
were
fleshed
and
the
incidence
of
scars,
assumed
to
be
caused
by
biting,
was
recorded
from
the
leather
side
of
the
fleshed
skins
on
a
subjective
scale
from
zero
to
five:
0
=
no
scars;
1
=
one
to
three
single
small
scars
or
red
spots;
2
=
more
than
three
single
scars
or
red
spots;
3
=
as
2,
but
in
addition
small
areas
of
an
incalcul-
able
number
of
scars
or
spots;
4
=
large
areas
of
an
incalculable
number
of
scars
or
spots;
5
=
almost
the
whole
skin
covered
by
scars
and
spots
(Hanninen
et
al.,
2008).
The
skins
were
dried
in
the
traditional
way
by
stretching
and
tacking
the
fleshed
skin
to
a
board
and
blowing
air
inside
the
skins
(Joergensen,
1985).
The
length
of
the
dried
skin,
i.e.
the
pelt,
was
measured
(accuracy
±
0.5
cm)
from
the
tip
of
the
nose
to
the
base
of
the
tail.
The
severity
of
fur
chewing
separately
in
tail
and
body
was
analysed
from
the
pelts
using
a
subjective
scale
from
zero
to
five:
0
=
no
damage,
1
=
really
minor
damage,
2
=
minor
damage,
3
=
moderate
damage,
4
=
quite
severe
damage
and
5
=
severe
damage
(Hanninen
et
al.,
2008).
The
pelts
were
sent
to
an
auction
company,
the
Finnish
Fur
Sales
Co.,
Ltd,
and
professionals
of
the
company
scored
the
'general
impression'
of
the
pelt
from
1
(poorest)
to
10
(best)
and
recorded
fur
defects
(feed
stains,
bites
and
wet
belly).
The
prices
of
the
pelts
were
also
obtained
from
the
Finnish
Fur
Sales
Co.,
Ltd.
Statistical
analyses
and
presentation
of
the
results
The
pooled
data
from
2
years
were
used
to
gain
better
statistical
power
and
to
enable
better
generalisability
of
the
conclusions.
For
each
GH
litter,
there
was
a
PH
litter
matched
for
litter
size
and
age
of
the
kits,
so
these
matched
litters
were
treated
as
dependent
on
each
other
in
the
statistical
analyses.
Littermates
were,
of
course,
not
independent
of
each
other.
The
data
concerning
body
mass,
pelt
length,
adrenal
mass,
serum
cortisol
level
after
administration
of
ACTH,
scars,
fur
chewing,
fur
defects,
general
impression
of
pelt
and
pelt
price
were
collected
for
individual
animals,
whereas
the
values
of
the
remaining
variables,
i.e.
behavioural
data,
dirtiness
of
nest
boxes
and
feed
consumption,
originated
from
litters
of
six
siblings.
For
these
reasons,
n
(i.e.
the
number
of
experimental
units)
varies
between
statistical
analyses,
although
the
data
came
originally
from
149-156
(some
data
missing)
animals.
The
effects
of
experimental
group
and
sex
on
body
mass,
pelt
length,
adrenal
mass,
serum
cortisol
level,
pelt
price
and
fur
defects
were
analysed
with
a
linear
mixed
model
(SPSS
statistical
software;
SPSS
Inc.,
Chicago,
IN,
USA)
(n
=
149-156).
Litter
and
matched
pair
were
used
as
ran-
dom
factors
to
take
into
account
the
dependence
of
animals
within
litters
and
matched
pairs.
The
average
pelt
price
of
the
auction
was
used
as
a
covariate
for
pelt
price
to
correct
for
the
average
price
differences
between
the
auctions.
Body
mass
in
December
was
used
as
a
covariate
when
analysing
the
adrenal
mass,
serum
cortisol
level
and
pelt
price.
The
pelt
price
was
also
tested
without
the
covariate.
The
percentages
of
mink
with
fur
defects
within
a
litter
and
sex
were
calculated
for
comparisons
between
housing
methods
and
sexes
with
the
linear
mixed
model
(n
=
52).
Data
concerning
social
interactions
and
stereotyped
pacing
were
analysed
with
the
linear
mixed
model
(n
=
26)
with
post
-hoc
tests
with
matched
pair
as
random
factors.
The
feed
consumption
data
were
analysed
with
the
paired
-
samples
t
-test
(n
=
13).
The
other
variables,
i.e.
scars,
fur
chewing,
general
impression,
mortality,
behavioural
data
and
nest
box
tidiness,
were
tested
with
nonparametric
tests.
Because
of
the
dependence
between
animals
within
each
litter
and
each
matched
pair,
the
data
from
individual
animals
were
combined
by
calculating
mean
values
from
the
values
of
individual
animals
before
testing
for
differences
in
scars,
fur
chewing
and
general
impression.
This
was
done
separately
for
both
sexes
within
each
litter
to
enable
gender
comparisons.
Thus,
four
dependent
variables
were
produced
for
each
of
these
para-
meters:
GH
males,
GH
females,
PH
males
and
PH
females.
The
number
of
kits
that
died
and
the
number
of
litters
with
deaths
were
compared
between
the
housing
systems
with
Fisher's
exact
test.
The
fur
chewing,
scar
score
and
general
impression
data
were
analysed
with
both
the
Friedman
two-way
analyses
of
variance
(henceforth
the
Friedman
test)
test
with
post
-hoc
tests
for
pair
-wise
comparisons
of
the
four
groups
(as
pre-
sented
in
Siegel
and
Castellan,
1988),
and
the
Wilcoxon
matched
-pairs
test
(henceforth
the
Wilcoxon
test)
with
Bonferroni
correction
to
compare
the
two
experimental
groups
(sexes
pooled)
and
the
two
sexes
(groups
pooled).
Activity
and
resting
in
the
cage,
and
the
time
spent
in
the
nest
box
were
compared
between
the
groups
and
between
the
months
with
the
Friedman
test.
Pair
-wise
comparisons
between
groups
within
months
and
between
months
within
groups
were
carried
out
with
a
post
-hoc
test
as
presented
in
Siegel
and
Castellan
(1988).
The
nest
box
tidiness
data
were
compared
with
the
Wilcoxon
test
if
the
experimental
groups
were
compared
within
months,
and
with
the
Friedman
test
if
time
trends
(i.e.
repeated
measurements)
were
analysed.
The
number
of
experimental
units,
i.e.
n,
was
13
in
all
the
nonparametric
analyses.
The
results
are
presented
as
estimated
marginal
mean
±
s.e.
of
estimate
(EMM
±
Syx)
or
mean
±
s.e.
of
mean
s.e.).
The
level
of
statistical
significance
was
set
at
the
conventional
0.05,
but
to
facilitate
readers'
opportunities
to
do
their
own
interpretations
of
the
results,
the
exact
P
-values
are
indicated
every
time
the
value
is
between
0.05
and
0.1
(whenever
this
is
possible);
ns
indicates
non-
significant
differences
(P>
0.1).
Results
Two
GH
females
and
one
PH
female
escaped
from
their
cages.
Furthermore,
two
PH
males
and
one
PH
female
died,
and
in
the
autopsy
they
all
were
found
to
have
fatty
livers
and
stomach
ulcers.
One
PH
female
had
to
be
euthanised
during
the
experiment
because
of
a
seizure
of
some
kind.
There
was
no
difference
in
mortality
between
the
groups
(4/78
animals
in
3/13
PH
litters
v.
0/78
animals
in
0/13
GH
litters,
P>
0.1,
Fisher's
exact
test).
1812
Group
housing
of
juvenile
farmed
mink
Table
1
Growth,
adrenal
function
and
pelt
characteristics
in
mink
kits
housed
either
in
pairs
(PH)
or
as
litters
(GH)
Males
Females
Significance
GH
PH
GH
PH
G
S
GxS
Number
of
animals
Growth
39
37
to
39
37
to
39
36
to
39
BM
in
July
(kg)
1
0.65
±
0.026
0.64
±
0.026
0.53
±
0.026
0.51
±
0.026
ns ns
BM
in
August
(kg)
1
1.33
±
0.029
1.36
±
0.029
0.93
±
0.029
0.91
±
0.029
ns
***
ns
BM
in
September
(kg)
1
2.35
±
0.062
2.55
±
0.062
1.37
±
0.062
1.38
±
0.062
P
=
0.076
***
**
BM
in
October
(kg)
1
2.53
±
0.060
2.85
±
0.060
1.45
±
0.061
1.52
±
0.061
*
***
**
BM
in
December
(kg)
1
2.62
±
0.053
2.97
±
0.054
1.41
±
0.054
1.52
±
0.054
**
**
Adrenal
function
Cortisol
(nmol/I)
A
1
366
±
29.5
349
±
35.6
448
±
33.8
478
±
32.0
ns
*
ns
Mass
of
adrenals
(mg)
A
•'
146
±
5.8
149
±
7.5
111
±7.0
111
±6.4
ns
***
ns
Pelt
Pelt
length
(cm)
1
78
±
0.7
80
±
0.7
64
±
0.7
64
±
0.7
P
=
0.057
*** **
Pelt
price
(EUR)
B
•'
17.1
±
1.55
22.3
±
1.69
19.2
±
1.69
21.5
±
1.64
P
=
0.062
ns
*
Fur
chewing
in
body
(scores
0
to
5)
2
1.0
±
0.40
0.1
±0.06
1.3
±
0.05
0.4
±
0.19
ns
Fur
chewing
in
tail
(scores
0
to
5)
2
1.0
±
0.31
0.5
±
0.20
1.1
±
0.40
0.7
±
0.26
ns
Fur
defects
(%
of
skins)'
56
±
10.3
17
±
10.3
56
±
10.3
33
±
10.3
ns ns
Scars
(scores
0
to
5)
2
3.1
±
0.37ab
2.2
±
0.35
b
3.4
±
0.35
a
2.1
±
0.35
b
**
General
impression
(scores
1
to
10)
2
5.6
±
0.47
a
6.9
±
0.31
ab
5.5
±
0.62
ab
7.5
±
0.37
b
See
Material
and
methods
for
the
details
of
the
variables.
BM
=
body
mass,
S
=
sex,
G
=
group.
(non
-significant),
P>0.1,
*P<0.05,
**P<0.01,
***P<0.001.
A
BM
in
December
as
a
covariate.
B
Average
prices
in
auctions
as
a
covariate.
1
Linear
mixed
model
(n=
52
in
fur
defects,
n=
149
to
156
in
other
parameters,
estimated
marginal
mean
±
Sy.x).
2
Friedman
two
way
analyses
of
variance
(n
=
13,
mean
±
s.e.,
Friedman
test
results
presented
in
G
x
S
column
and
post
-hoc
results
as
lower
case
superscript
letters:
means
with
no
common
letter
differ
at
P<
0.05
in
scars
and
P
<
0.1
in
general
impression).
Sexual
dimorphism
could
be
seen
in
all
size
parameters
(Table
1).
PH
mink
were
heavier
at
pelting
than
GH
mink
and
their
pelts
tended
to
be
longer
than
those
of
GH
mink,
in
both
sexes.
There
were
no
differences
between
the
groups
in
adrenal
function,
i.e.
serum
cortisol
level
2
h
after
ACTH
administration
or
adrenal
mass.
The
groups
did
not
differ
in
the
severity
of
fur
chewing
in
tail
or
body
when
all
four
groups
(i.e.
GH
males,
GH
females,
PH
males
and
PH
females)
were
compared
(Table
1),
but
the
Wilcoxon
test
showed
a
weak
tendency
for
a
difference
in
fur
chewing
in
the
body
between
housing
systems
(sexes
pooled
within
housing
systems;
GH
=
1.1
±
0.41
v.
PH
=
0.3
±
0.09,
P=
0.092,
the
Wilcoxon
test).
The
general
impression
of
the
pelt
tended
to
be
worse
in
GH
males
than
in
PH
females
(Table
1).
The
GH
females
tended
to
have
more
scars
in
their
skins
than
the
PH
females
and
PH
males,
whereas
the
GH
males
did
not
differ
from
any
of
these.
The
GH
animals
had
worse
general
impression
of
the
pelt
(GH
5.6
±
0.51
v.
PH
7.2
±
0.31)
and
more
scars
(GH
2.9
±
0.25
v.
PH
1.7
±
0.21)
in
their
skins
than
the
PH
animals
(P
<
0.05
for
both,
the
Wilcoxon
test),
but
there
was
no
difference
(P>
0.1)
between
the
sexes
in
either
of
the
parameters
(general
impression:
males
6.2
±
0.34
v.
females
6.5
±
0.32,
scars:
males
2.2
±
0.22
V.
females
2.3
±
0.28).
In
most
of
the
cases
when
the
scar
score
was
between
one
and
three
(i.e.
moderate
severity
of
scars),
the
scars
were
on
the
neck
area.
The
GH
mink
had
more
fur
defects
than
the
PH
mink
(Table
1).
The
price
of
the
pelts
tended
to
be
lower
in
the
GH
than
in
the
PH
animals
(Table
1),
but
the
difference
disappeared
when
the
body
mass
in
December
was
used
as
a
covariate.
The
extent
of
the
use
of
the
various
parts
of
the
cages
did
not
differ
between
the
groups
in
August,
whereas
in
November
the
GH
mink
tended
to
spend
more
time
resting
on
the
cage
(including
the
platform)
than
the
PH
mink
(Figure
2).
Both
groups
were
more
active
in
the
cage
in
August
than
in
November.
The
PH
mink
spent
more
time
in
the
nest
box
and
rested
less
in
the
cage
in
November
than
in
August,
while
no
such
difference
was
seen
in
the
GH
mink.
Taking
both
observation
months
together,
there
was
no
overall
difference
in
the
frequency
of
social
interactions
between
the
groups,
but
the
frequency
decreased
more
from
August
to
November
in
pair
-housed
than
in
group
-
housed
mink,
leading
to
differences
between
the
groups
in
November
(Figure
3).
The
group
X
time
interaction
in
social
interactions
disappeared
(P>
0.1,
linear
mixed
model
with
post
-hoc
tests)
and
the
difference
between
the
groups
in
November
decreased
to
a
tendency
(P=
0.052)
when
activity
in
the
cage
was
used
as
a
covariate.
The
frequency
of
stereotyped
behaviour
increased
from
August
to
November
and
was
more
frequent
in
pair
-housed
than
in
group
-housed
animals,
especially
in
November.
The
group
X
time
interaction
in
stereotyped
behaviour
became
1813
Hanninen,
Ahola,
Pyykonen,
Korhonen
and
Mononen
`Yo
of
observations
100
-
80
-
60
-
40
-
20
-
ns
PH
GH
GH
"
GH
ns
PH
H*
*
PH
"
ns
ns
Aug
Nov
Active
in
the
cage
Ii
0
Aug
I
Nov
Resting
in
the
cage
GH
ns
/
PH
A
*
ns
ns
T
Aug
Nov
In
the
nest
box
I I I
Aug
Nov
Not
known
Figure
2
Activity
and
resting
in
the
cage
and
use
of
the
nest
boxes
in
pair-
(PH)
and
group-
(GH)
housed
mink
in
August
(T
a
=
+10°C
to
+25°C)
and
November
(T
a
=
-6°C
to
+6°C)
(mean+s.e.).
The
differences
between
the
groups
within
months
are
indicated
above
the
columns
in
bold
and
the
within
-
group
difference
between
months
above
the
brackets
(Friedman
two-way
analyses
of
variance
and
post
-hoc
tests).
ns,
P>
0.1,
°P<
0.1,
*P<0.05.
Statistically
n=
13,
i.e.
the
number
of
matched
litters,
although
the
data
are
originally
from
149-156
animals.
%
of
observations
50
-
40
-
30
-
20
-
10-
0
50
-
2
40-
0
2
30
-
.9
-8
20
-
0
10-
0
Social
interactions
PH
***
0
GH***
Group
ns
Time
***
Group
x
Time
*
ns
August
Stereotyped
pacing
November
Group
**
Time
***
Group
x
Time
ns
ns
MIME
T
August
***
T
November
Figure
3
Social
interactions
and
stereotyped
pacing
in
pair-
(PH)
and
group-
(GH)
housed
mink
in
August
and
November
(estimated
marginal
mean
±
Sy.x).
The
differences
between
the
groups,
and
the
effects
of
time
and
group
X
time
interactions
are
presented
in
the
plot
areas,
the
differences
between
the
groups
within
the
months
above
the
bars,
and
the
differences
between
the
months
within
the
groups
in
the
legend
box
(linear
mixed
model
with
post
-hoc
tests).
ns,
P>
0.1,
*P<0.05,
**P<0.01,
***P<0.001.
Statistically
n=
52,
although
the
data
are
originally
from
26
litters,
i.e.
149-156
animals.
significant
(P<
0.05)
when
activity
in
the
cage
was
used
as
a
covariate.
The
nest
boxes
were
dirtier
in
the
GH
group
than
in
the
PH
group
in
the
late
autumn,
and
the
dirtiness
increased
with
time
in
the
GH
group
but
not
in
the
PH
group
(Figure
4)
(for
brevity,
results
from
only
four
out
of
the
nine
recordings
are
presented).
The
PH
animals
had
cleaner
nest
boxes
than
the
GH
animals,
and
the
number
of
clean
nest
boxes
decreased
with
time
in
the
GH
group
but
not
in
the
PH
group.
Feed
consumption
of
PH
and
GH
animals
was
equal
in
September
(311
g
±
14.3
g
v.
289
g
±
10.4
g
feed
per
animal
per
day,
P>
0.1,
paired
-samples
t
-test,
n=
13
matched
pair
litters),
but
the
PH
animals
consumed
more
feed
than
the
GH
animals
in
November
(285
±
20.3
v.
225
±
19.0
g,
P<
0.01).
Discussion
Welfare
Both
direct
behavioural
observations
(Hansen
et
al.,
1997;
Pedersen,
1999;
Pedersen
et
al.,
2004;
Hanninen
et
al.,
2008,
the
present
study)
and
indirect
observations
based
on
skin
and
fur
damages
(Pedersen,
1999;
Hansen
and
Houbak,
2005;
Hanninen
et
al.,
2008,
the
present
study)
indicate
that
there
is
more
aggression,
or
social
encounters
resulting
in
skin
damages
(see
discussion
below),
in
group
-
housed
than
in
pair
-housed
mink.
However,
the
severity
of
aggression
varies
greatly
between
the
studies:
in
seven
studies,
aggression
problems
have
been
mild
(Hansen
et
al.,
1997;
Hansen
and
Houbak,
2005; Lindberg
et
al.,
2007;
Hanninen
et
al.,
2008,
the
present
study)
or
not
directly
1814
P=0.084
** **
Group
housing
of
juvenile
farmed
mink
2.5
-
PH
ns
GH
***
PH
ns
1.5
-
cr)
GH
***
**
0.5
-
I
August
October
November
December
Figure
4
The
number
of
clean
nest
boxes
(bars,
possible
range
zero
to
three)
and
the
dirtiness
score
of
the
nest
boxes
(lines,
possible
range
zero
to
four)
in
pair-
(PH)
and
group-
(GH)
housed
juvenile
mink
litters
(mean
+
s.e.)
The
differences
between
the
groups
in
the
number
of
clean
nest
boxes
(above
the
bars)
and
in
the
dirtiness
score
of
the
boxes
(above
the
GH
line)
are
indicated
for
each
month
(the
Wilcoxon
matched
-pair
test).
The
effect
of
time
on
the
number
of
clean
nest
boxes
and
dirtiness
score
of
the
boxes
(Friedman
two-way
analyses
of
variance)
within
each
group
are
indicated
in
the
legend
box.
ns,
P>
0.1,
*P<0.05,
**P<0.01,
***P<0.001.
Statistically
n=
13,
i.e.
the
number
of
matched
litters,
although
the
data
are
originally
from
149-156
animals.
reported
and
therefore
putatively
absent
or
mild
(Jonge
de,
1996;
Vinke
et
al.,
2002),
whereas
in
two
studies
aggres-
sion
led
to
high
mortality
rates
(Pedersen,
1999;
Pedersen
et
al.,
2004).
Interestingly,
the
two
studies
with
major
aggression
problems
were
carried
out
with
pearl
and
pastel
colour
types
of
mink,
and
all
other
studies
with
brown
or
wild
colour
type,
except
for
Lindberg
et
al.
(2007),
which
was
with
demi
puff
and
half
-sapphire.
It
is
known
that
coat
colour
correlates
with
behaviour
in
mammals
in
general
(see
a
review
in
Hemmer,
1990)
and
also
in
mink
(see
a
review
in
Voitenko
and
Trapezov,
2001),
but
it
remains
to
be
elucidated
whether
the
coat
colour
per
se
or
temperament
differences
not
related
to
the
colour
type
between
various
mink
populations
is
the
primary
reason
for
differences
in
aggressive
behaviour.
On
the
other
hand,
no
matter
what
the
underlying
rea-
sons
for
these
population
differences
are,
the
possibility
of
dramatic
negative
effects
on
the
welfare
of
mink
has
to
be
born
in
mind
when
considering
group
housing
as
an
alter-
native
to
the
traditional
pair
housing.
Group
housing
would
necessitate
better
supervision
of
the
animals
on
farms,
and
perhaps
choosing
less
aggressive
animals
for
breeding.
This
would
be
especially
important
if
the
stocking
density
was
higher
than
two
animals
per
standard
cage.
According
to
the
European
Convention
(1999),
it
is
allowed
to
keep
eight
mink
in
a
row
cage
formed
by
connecting
three
standard
cages
to
each
other.
The
reason
that
the
higher
frequency
of
seemingly
aggressive
behaviour
in
the
group
-housed
animals
compared
with
pair
-housed
animals
has
not
caused
higher
mortality
in
most
studies
might
be
that
the
mink
are
actually
(or
at
least
partly)
playing,
not
fighting.
The
so-called
'social
biting
play'
(Vinke
et
al.,
2005)
may
be
easily
confused
with
true
fighting
and
it
can
probably
also
cause
scars
to
the
skin.
The
fact
that
mink
spend
most
of
their
time
out
of
sight
in
nest
boxes
(Jeppesen
et
al.,
2000;
Pedersen
et
al.,
2004,
the
present
results)
may
bias
the
results
from
behavioural
observations.
The
difference
in
the
frequency
of
social
interactions
observed
in
the
present study
in
November
lost
statistical
significance
when
total
time
spent
active
in
the
cage
was
used
as
a
covariate
in
the
statistical
analysis.
In
other
words,
the
analysis
without
the
covariate
may
have
exaggerated
the
difference
between
the
groups.
The
nest
boxes
are
certainly
large
enough
to
enable
mink
to
fight
(or
play)
in
them.
Accordingly,
indirect
measures
of
aggression,
i.e.
fur
and
skin
damages,
may
be
more
reliable
than
behavioural
observations
based
on
the
behaviour
outside
the
nest
box
only.
Behavioural
stress
indicators
have
shown
that
stress
levels
are
equal
or
even
lower
in
group
-housed
juvenile
mink
than
in
pair
-housed
juveniles.
Fur
chewing
and
in
particular
tail
biting
can
be
regarded
as
self
-mutilation,
i.e.
as
an
indicator
of
poor
welfare
in
mink
(Hansen
et
al.,
1998).
There
is
less
tail
biting
and
an
equal
level
of
fur
chewing
in
groups
compared
with
pairs
(Pedersen,
1999;
Pedersen
et
al.,
2004;
Hansen
and
Houbak,
2005;
Lindberg
et
al.,
2007).
The
frequency
of
stereotypies,
a
sign
of
frustration
and
poor
welfare
(e.g.
Mason
and
Latham,
2004),
has
been
reported
to
be
equal
in
group
-housed
and
pair
-housed
mink
(Hansen
et
al.,
1997;
Pedersen,
1999,
Vinke
et
al.,
2002;
Pedersen
et
al.,
2004;
Lindberg
et
al.,
2007;
Hanninen
et
al.,
2008)
or
even
slightly
lower
in
group
than
in
pair
housing
(Jeppesen
et
al.,
2000,
the
present
study).
However,
the
relation
between
stereotypic
beha-
viour
and
welfare
is
ambiguous
(Mason
and
Latham,
2004).
For
example,
in
the
present
study,
social
tension
may
have
hindered
the
development
of
stereotypic
behaviour
in
group
-housed
mink.
1815
Hanninen,
Ahola,
Pyykonen,
Korhonen
and
Mononen
In
contrast
to
behavioural
signs
of
stress,
adrenal
func-
tion
results
are
less
consistent
between
various
studies:
no
differences
between
group
and
pair
housing
(the
present
study),
lower
adrenal
mass
and
response
to
the
ACTH
in
group
housing
(Hanninen
et
al.,
2008),
and
higher
adrenal
mass
(Vinke
et
al.,
2002)
and
higher
level
of
plasma
cortisol
in
female
kits
(Hansen
and
Damgaard,
1991)
in
group
housing
have
been
observed.
These
discrepancies
between
studies
may
reflect
rather
the
problem
of
using
adrenal
function
as
a
stress
indicator
in
general
(c.f.
Rushen,
1991)
and
in
mink
(Hanninen
et
al.,
2008)
than
true
differences
in
stress
levels
between
the
experimental
groups
in
the
various
studies.
Production
The
present
results
show
that
stress
-related
own
-fur
chewing
was
not
statistically
different
in
group-
and
pair
-housed
ani-
mals,
whereas
aggression
or
play
-related
damages
are
more
frequent
in
group
-housed
than
in
pair
-housed
animals.
The
net
effect
on
production
is
that
pelts
from
group
-housed
mink
have
a
higher
frequency
of
fur
defects
(Hanninen
et
al.,
2008,
the
present
study)
and
lower
general
impression
(Lindberg
et
al.,
2007,
the
present
study).
These
differences
did
not,
however,
have
a
statistically
significant
effect
on
the
prices
of
the
pelts
in
the
present
study.
Besides
pelt
quality,
another
crucial
factor
affecting
the
prices
of
the
pelts
is
pelt
length.
The
body
mass
has
been
reported
to
be
either
equal
in
group
-housed
and
pair
-
housed
mink
(Jonge
de,
1996;
Vinke
et
al.,
2002;
Hanninen
et
al.,
2008)
or
slightly
lower
in
group
housing
than
in
pair
housing
in
males
(Pedersen,
1999)
or
in
both
sexes
(the
present
study).
Although
the
body
mass
may
be
lower
to
some
extent
in
group
-housed
than
in
pair
-housed
mink,
pelt
length
is
equal
(Pedersen,
1999;
Hanninen
et
al.,
2008)
or
the
difference
between
experimental
groups
is
minimal
(2
cm
in
males
and
no
difference
in
females;
the
present
study)
as
compared
to
the
6
cm
difference
between
the
size
classes
in
the
auctions.
The
lower
body
mass
in
group
-housed
mink
results
at
least
partially
from
group
-housed
mink
consuming
less
feed
than
pair
-housed
mink
(Hanninen
et
al.,
2008,
the
present
study).
Combined
with
the
almost
equal
pelt
length
in
pairs
and
in
groups,
this
may
indicate
that
pair
-housed
mink
gather
more
fat
than
group
-housed
mink.
In
mink,
most
fat
deposits
are
gathered
as
subcutaneous
fat,
which
acts
as
additional
insulation
for
this
semiaquatic
species
(Nieminen
et
al.,
2006).
It
is
possible
that
this
additional
insulation
is
more
important
for
pair
-housed
than
for
group
-housed
mink,
since
group
-housed
mink
may
have
thermoregulatory
benefits
from
being
able
to
utilise
huddling.
For
mink
kits,
huddling
is
an
effective
way
of
reducing
energy
loss,
especially
because
of
their
short
hair
and
elongated
and
thin
body
shape
(Tauson
et
al.,
2006).
Our
earlier
family
housing
experiment
showed
that
mink
housed
in
groups
spent
most
of
their
time
huddled
together
(mainly
in
the
nest
box)
when
the
ambient
temperature
dropped
to
near
or
below
zero
(Hanninen
et
al.,
2008).
Interestingly,
the
group
-housed
mink
clearly
keep
at
least
one
of
their
nest
boxes
clean
and
dry
(Hanninen
et
al.,
2008,
the
present
results).
Nest
boxes
with
dry
bedding
are
an
important
prerequisite
for
successful
behavioural
thermoregulation
in
farmed
mink
(Korhonen
and
Harri,
1984),
and
keeping
typically
only
one
nest
box
clean
also
in
the
present study
(see
Figure
1)
may
indicate
that
the
mink
rested
in
that
nest
box
in
a
huddle.
Unfortunately,
this
could
not
be
confirmed
from
the
video
observations,
because
it
was
impossible
to
see
into
the
nest
boxes,
where
most
resting
and
conse-
quently
also
huddling
occur.
It
could
be
hypothesised
that
the
dirtiness
of
the
nest
boxes
might
have
forced
the
mink
to
huddle
together
in
only
one
nest
box.
On
the
other
hand,
the
mink
huddled
together
also
when
resting
in
the
cage.
Conclusions
Although
the
incidence
of
scars
showed
that
there
might
have
been
more
aggressive
behaviour
among
the
group
-
housed
than
among
the
pair
-housed
mink,
this
was
not
observed
unambiguously
in
behavioural
observations,
and,
at
least,
aggression
did
not
cause
mortality
or
serious
injuries
to
the
animals.
It
is
also
possible
that
social
biting
play
may
be
erroneously
interpreted
as
aggression
in
mink.
In
addition,
the
housing
system
did
not
affect
pelt
size,
and
although
the
quality
of
the
pelts
was
slightly
lower
in
group
-housed
than
in
pair
-housed
mink,
there
was
only
a
tendency
for
lower
pelt
prices.
The
lower
pelt
prices
might
even
be
partially
compensated
for
by
the
group
-housed
mink
eating
10%
to
20%
less
in
the
late
autumn,
due
to
thermoregulatory
benefits,
than
their
pair
-housed
con
-
specifics.
The
group
-housed
animals
were
possibly
less
stressed
than
the
pair
-housed
animals,
but
these
results
were
not
unambiguous.
Acknowledgements
This
study
was
supported
by
the
Finnish
Cultural
Foundation.
We
are
grateful
to
Maija
Miskala,
Matti
Tengvall
and
Rose
-Marie
Nybondas
for
their
skillful
assistance
when
taking
care
of
the
animals
and
collecting
the
data
and
for
Seppo
Kukkonen
for
performing
the
biochemical
analyses.
Finnish
Fur
Sales
Co.,
Ltd
is
acknowledged
for
providing
us
with
skin
quality
and
price
data.
Two
anonymous
referees
are
acknowledged
for
their
constructive
comments
on
the
manuscript
of
the
present
paper.
References
Arts
1,
Vinke
CM,
Houx
BB,
de
Buisonje
F,
van
den
Bos
R
and
Spruijt
BM
2004.
Effects
of
group
housing
and
cage
enrichment
on
physiology
and
behaviour
of
farmed
mink
(Mustela
vison).
In
Cage
enrichments
and
welfare
of
farmed
mink
(ed.
CM
Vinke).
PhD,
Utrecht
University,
pp.
105-129.
Birks
1
1986.
Mink.
The
mammal
society.
Anthony
Nelson
Ltd,
Shropshire,
UK.
Broom
DM
and
Johnson
KG
1993.
Stress
and
animal
welfare.
Chapman
&
Hall,
London,
UK.
Damgaard
BM
and
Hansen
SW
1996.
Stress
physiological
status
and
fur
properties
in
farm
mink
placed
in
pairs
or
singly.
Acta
Agriculture=
Scandinavica
Section
A
Animal
Science
46,253-259.
Dunstone
N
1993.
The
mink.
T
&
AD
Payser,
London,
UK.
1816
Group
housing
of
juvenile
farmed
mink
European
Commission
2001.
The
welfare
of
animals
kept
for fur
production.
Report
of
the
Scientific
Committee
on
Animal
Health
and
Animal
Welfare.
European
Commission,
Health
&
Consumer
Protection
Directorate
-
General.
Directorate
C
-
Scientific
Opinions.
C2
-
Management
of
Scientific
Co
-
Operation
and
Networks.
Adopted
on
12-13
December
2001.
European
Convention
1999.
European
Convention,
Standing
committee
of
the
European
convention
for
the
protection
of
animals
kept
for
farming
purposes
(T
-AP).
Recommendations
concerning
fur
animals,
The
Standing
Committee.
36th
Meeting,
Strasbourg,
22-25
June
1999.
Finnish
Fur
Breeders'
Association
2008.
Minkinnahkojen
tarjontamaarat
maail-
manmarkkinoilla
v.
2005-2007.
Retrieved
July
17,
2008,
http://www.stkl-fpf.fi/
mod
ules/system/stdreq.aspx?P
-64&VI
D-default&SI
D
-381053956340420&S
=
0&C-22127
(in
Finnish).
Gomez
F,
Lahmame
A,
de
Kloet
ER
and
Armario
A
1996.
Hypothalamic
-
pituitary
-adrenal
response
to
chronic
stress
in
five
inbred
strains:
differential
responses
are
mainly
located
at
the
adrenocortical
level.
Neuroendocrinology
63,
327-337.
Hanninen
S,
Mononen
1,
Harjunpaa
S,
Pyykonen
T,
Sepponen
1
and
Ahola
L
2008.
Effects
of
family
housing
on
some
behavioural
and
physiological
parameters
of
juvenile
farmed
mink
(Mustela
vison).
Applied
Animal
Behaviour
Science
109,
384-395.
Hansen
SW
and
Damgaard
BM
1991.
Stress
physiological,
haematological
and
clinical
-chemical
status
of
farm
mink
placed
in
groups
or
singly.
Acta
Agriculture=
Scandinavica
Section
A
Animal
Science
41,
355-366.
Hansen
SW
and
Houbak
B
2005.
To
skridt
frem
og
tre
tilbage
-
gruppeindhusning
of
mink.
In
Faglig
Arsberetning
2004
(ed.
P
Sandbol),
pp.
39-47.
Pelsdyrerhvervets
Forsogs-
og
ForskningsCenter,
Holstebro,
Danmark.
Hansen
SW,
Houbak
B
and
Malmkvist
1
1997.
Does
the
'solitary'
mink
benefit
from
having
company?
Nordiska
jordbruksforskares
forening,
Utredning,
Rapport
nr.
116,
NJF
seminarium
nr.
280.
NJF,
Helsinki,
Finland.
Hansen
SW,
Houbak
B
and
Malmkvist
1
1998.
Development
and
possible
causes
of
fur
damage
in
farm
mink
-
significance
of
social
environment.
Acta
Agriculture=
Scandinavica
Section
A
Animal
Science
48,
58-64.
Hemmer
H
1990.
Domestication:
the
decline
of
environmental
appreciation,
2nd
edition.
Cambridge
University
Press,
Cambridge,
UK.
Hemsworth
PH,
Barnett
JL
and
Campbell
RG
1996.
A
study
of
the
relative
aversiveness
of
a
new
daily
injection
procedure
for
pigs.
Applied
Animal
Behaviour
Science
49,
1996.
Jeppesen
LL,
Heller
KE
and
Dalsgaard
T
2000.
Effects
of
early
weaning
and
housing
conditions
on
the
development
of
stereotypes
in
farmed
mink.
Applied
Animal
Behaviour
Science
68,
85-92.
Joergensen
G
(ed.)
1985.
Mink
production.
Scientifur.
K.
Larsen
&
Son,
Glostrup,
Denmark.
Jonge
de
G
1996.
A
new
housing
system
for
mink.
Progress
in
fur
animal
science,
animal
production
review,
Polish
Society
of
Animal
Production
(Warsaw).
Applied
Science
Report
29,
45-51.
Korhonen
H
and
Harri
M
1984.
Thermophysical
properties
of
nests
of
farm
mustelids:
thermal
insulation.
Scientifur
8,
285-290.
Lindberg
H,
Alden
E
and
Lidfors
L
2005.
Group
housed
mink
-
effect
on
welfare
and
production.
Conference
at
the
Autumn
Meeting
of
the
Nordic
Association
of
Agricultural
Scientists,
Subsection
for
Fur
Animals,
Seminar
no.
377,
Uppsala,
Sweden,
2
pp.
Lindberg
H,
Hansen
S,
Alden
E
and
Lidfors
L
2007.
Effects
of
climbing
cages
and
group
size
on
behaviour
and
production
in
juvenile
mink.
Conference
at
the
Autumn
Meeting
of
the
Nordic
Association
of
Agricultural
Scientists,
Subsection
for
Fur
Animals,
Seminar
no.
403,
Kolding,
Denmark,
6
pp.
Martin
P
and
Bateson
P
1993.
Measuring
behaviour.
Cambridge
University
Press,
Cambridge,
UK.
Mason
al
and
Latham
NR
2004.
Can't
stop,
won't
stop:
is
stereotypy
a
reliable
animal
welfare
indicator?
Animal
Welfare
13,
S57
-S69.
Ministry
of
Agriculture
and
Forestry
1999.
Decision
on
animal
welfare
requirements
for fur
animals.
16/VFO/1999.
Retrieved
July
17,
2008,
http://
www.mmm.fi/el/laki/f/f26.html
(in
Finnish).
Moller
SH
1991.
Weight
gain
and
hair
chewing
in
mink
kits
placed
singly
or
in
pairs
from
September.
Scientifur
15,
21-27.
Niemimaa
1
and
Pokki
1
1997.
Minkki.
In
Suomen
luonto,
Elaimet,
Nisakkaat
(ed.
1
Lokki,
P
Nummi,
V
Neuvonen,
K
Miettinen
and
R
-L
Kuosmanen),
pp.
192-197
Weilin+Goos,
Porvoo,
Finland.
Nieminen
P,
Kakela
R,
Pyykonen
T
and
Mustonen
A
-M
2006.
Selective
fatty
acid
mobilization
in
the
American
mink
(Mustela
vison)
during
food
deprivation.
Comparative
Biochemistry
and
Physiology
Part
B
Biochemistry
and
Molecular
Biology
145,
81-93.
Nimon
Al
and
Broom
DM
1999.
The
welfare
of
farmed
mink
(Mustela
vison)
in
relation
to
housing
and
management:
a
review.
Animal
Welfare
8,
205-228.
Pedersen
V
1999.
Alternative
Burmiljoer
til
Mink
-
Hvad
er
Vore
Erfaringer?.
In
Faglig
Arsberetning
(ed.
P
Sandbol),
pp.
17-23.
Pelsdyrerhvervets
Forsogs-
og
ForskningsCenter,
Holstebro,
Danmark.
Pedersen
V,
Jeppesen
L
and
Jeppesen
N
2004.
Effects
of
group
housing
on
behaviour
and
production
performance
in
farmed
juvenile
mink
(Mustela
vison).
Applied
Animal
Behaviour
Science
88,
89-100.
Rushen
1
1991.
Problems
associated
with
the
interpretation
of
physiological
data
in
the
assessment
of
animal
welfare.
Applied
Animal
Behaviour
Science
28,
381-386.
Selye
H
1950.
The
physiology
and
pathology
of
exposure
to
stress.
Acta,
Inc.,
Medical
Publishers,
Montreal,
Canada.
Siegel
S
and
Castellan
NJ
Jr
1988.
Nonparametric
statistics
for
behavioral
sciences,
2nd
edition.
McGraw-Hill
International
Editions,
New
York,
USA.
Tauson
A
-H,
Chwalibog
A
and
Tygesen
MP
2006.
Late
development
of
homeothermy
in
mink
(Mustela
vison)
kits
-
a
strategy
for
maximum
survival
rate.
Journal
of
Animal
Physiology
and
Animal
Nutrition
90,
34-45.
Terlouw
EMC,
Schouten
WGP
and
Ladewig
1
1997.
Physiology.
In
Animal
welfare
(ed.
MC
Appleby
and
BO
Hughes),
pp.
143-158.
CAB
International,
University
Press,
Cambridge,
UK.
Tuori
M,
Kaustell
K,
Valaja
1,
Aimonen
E,
Saarisalo
E
and
Huhtanen
P
2000.
Rehutaulukot
ja
ruokintasuositukset
(Feed
tables
and
feeding
recommenda-
tions),
3rd
edition.
Yliopistopaino,
Helsinki,
Finland.
Vinke
CM,
Baars
A,
Spruijt
BM
and
Ruis
M
2002.
Do
family
group
housing
systems
improve
the
welfare
of
farmed
mink?
In
Proceedings
of
the
36th
International
Congress
of
the
ISAE
(ed.
P
Koene
and
Scientific
Committee),
164
pp.
Ponsen
and
Looijen,
Wageningen,
The
Netherlands.
Vinke
CM,
van
Leeuwen
1
and
Spruijt
BM
2005.
Juvenile
farmed
mink
(Mustela
vison)
with
additional
access
to
swimming
water
play
more
frequently
than
animals
housed
with
a
cylinder
and
platform,
but
without
swimming
water.
Animal
Welfare
14,
53-60.
Voitenko
NN
and
Trapezov
OV
2001.
Effect
of
four
coat
color
mutations
(Cr,
5,
5",
and
h)
on
brain
monoamine
oxidase
in
mink.
Russian
Journal
of
Genetics
37,
519-522.
1817