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Preference for bedding material in Syrian
hamsters
M Lanteigne and S G Reebs
De
´
partement de Biologie, Universite
´
de Moncton, Moncton, NB, E1A 3E9, Canada
Summary
This study aimed to determine whether Syrian (golden) hamsters, Mesocricetus auratus,
prefer certain bedding materials and whether bedding material can affect paw condition,
body weight gain and wheel-running activity. In a first experiment, 26 male hamsters had
access to two connected cages, each cage containing a different bedding material (either pine
shavings, aspen shavings, corn cob or wood pellets). In a second experiment, 14 male
hamsters had access to four connected cages that contained the different bedding materials
and also a piece of paper towel to serve as nest material. In a third experiment, 30 male
hamsters were each placed in a single cage, 10 of them with pine shavings, 10 with aspen
shavings and 10 with corn cob, and they were monitored for 50 days. Significant preferences
in the first experiment were: pine shavings over aspen shavings, corn cob over wood pellets,
pine shavings over corn cob and aspen shavings over wood pellets (aspen shavings versus
corn cob was not tested). However, there was no significant preference expressed in the
second experiment, suggesting that the general preference for shavings in the first
experiment was based on bedding material suitability as a nesting material. No significant
effect of bedding material on paw condition, body weight gain and wheel-running activity
was detected. None of the four bedding materials tested in this study can be judged to be
inappropriate in the short term if nesting material is added to the cage and if the litter is
changed regularly.
Keywords Syrian hamster; golden hamster; bedding material; nesting material; choice;
preference; animal welfare
Captivity conditions must satisfy the basic
needs of laboratory animals and ensure their
physical, physiological and psychological
welfare. Bedding material is an important
component of a laboratory animal’s
environment. It provides sanitary conditions
by absorbing body wastes. Inasmuch as
possible, it must not contain pesticides or
carcinogenic substances (Weisbroth 1979,
Raynor et al. 1983, Arnold & Estep 1994,
Van de Weerd et al. 1996). It must minimize
the production of ammonia by bacteria
(Perkins & Lipman 1995), as an excess of
ammonia can harm the trachea of animals
(Gambel & Clough 1976). Dust content of
bedding material can also be harmful and
cause allergies, respiratory problems and
cancers (Raynor et al. 1983, Arnold & Estep
1994, Potgieter & Wilke 1996).
Bedding may also double as a nesting
material and as a substrate on which to
walk. Comfort and suitability for nest
construction and body contact can therefore
become criteria in the choice of appropriate
bedding material. Animal preferences
for bedding material over others have
sometimes been interpreted in this
light (Blom et al. 1996, Ago et al. 2002).
Psychological needs such as comfort
Accepted 25 November 2005 r Laboratory Animals Ltd. Laboratory Animals (2006) 40, 410–418
Correspondence: Ste
´
phan Reebs.
Email: reebss@umoncton.ca
are often studied through preference
tests.
There has been a fair amount of research
on the preference for bedding material
exhibited by rats (Blom et al. 1996, Van de
Weerd et al. 1996, Ras et al. 2002) and mice
(Iturrian & Fink 1968, Mulder 1975, Blom
et al. 1996, Ago et al. 2002). In contrast, we
are aware of no such research on Syrian
(golden) hamsters, in spite of this animal’s
popularity in chronobiological as well as
some types of biomedical studies. In fact,
welfare studies on hamsters seem to be
limited to Arnold and Estep (1994) on cage
floor choice, Mrosovsky et al. (1998) and
Reebs and St-Onge (2005) on running wheel
choice, Kuhnen (1999) on cage size, and
Reebs and Maillet (2003) on environmental
enrichment. In the present study, we
investigated whether hamsters have a
preference for different types of bedding
material. We also looked at short-term
effects of bedding material on paw condition,
body weight gain and wheel running.
Experiment I
Material and methods
All experiments were conducted under
approval by the Universite
´
de Moncton’s
Animal Care Committee (protocol nos 03–01
and 04–08).
The preference apparatus consisted of two
translucent white cages (Nalgene, F-size for
rats, 47 26 20 cm) made of polypropylene
and connected by a plastic tube (Hagen’s
Habitrail; 6 cm diameter, vertical access
tunnel 19 cm long, connecting tunnel 37 cm
long). Each cage had a water bottle with
distilled water. Food pellets for laboratory
rodents (Hagen) were distributed on the floor
of each cage and replaced as needed. In each
cage was a running wheel (Nalgene, F-size
for rats, 35 cm in diameter) connected to a
computer system for recording daily running
activity. Bedding material was spread on the
floor of each cage. Thirteen such apparatus
were kept side by side on shelves in a single
room kept at 21711C, under a 14:10 h
light:dark cycle. Light was provided by two
incandescent lights on the ceiling of the
room, resulting in an intensity of about 100
lux within the cages.
Four common commercial bedding
materials were tested. Two were made of
wood shavings (one aspen, the other pine,
both from Rolf C Hagen Inc). Two more were
made of granules (one consisting of wood
pellets, i.e. small cylinders of wood 6 mm in
diameter and 5–25 mm long, from Kaytee Co;
the other made of bits of corn cob, about
2–5 mm in diameter, from Rolf C Hagen Inc).
A fifth type of commercially available litter,
rather granular in type (heat-treated
hardwood chips, ‘Beta-Chips’, Northeaster
Products) was not tested because this litter is
used by the farm that raises the hamsters we
purchase, and we wanted to minimize
possible bias caused by previous experience.
In a first experiment, we pitted the two
shaving types against each other, and did the
same with the two granular types. Thirteen
male hamsters, 60 days old, were purchased
from Charles River Canada (the number of
hamsters corresponded to the maximum
number of two-cage set-ups that could be
fitted in the room). Upon arrival in the
laboratory, each hamster was placed in a
preference apparatus, either in the right- or
the left-hand side, determined at random. At
that time, the cages did not contain any
bedding material. About 24 h later (sufficient
time for the hamsters to learn how to use the
connecting tubes), 1 L of bedding material
was added to each cage, irrespective of where
the hamster was at that time. For seven of
the hamsters, one cage (determined at
random) received pine shavings and the
other cage received aspen shavings; the other
six hamsters received wood pellets and corn
cob. Twelve days later, the litter was
changed: the hamsters that had received the
shavings pair now got the granular pair, and
vice-versa. Twelve days after that, the whole
cycle was repeated one more time (second
trial). Thus each hamster was twice given a
choice between aspen and pine shavings, and
twice between wood pellets and corn cob.
A second experiment was conducted with
13 new male hamster s, as above except that
the pairings involved pine shavings versus
corn cob (the two ‘winners’ of the pairings in
the first experiment) and aspen shavings
Laboratory Animals (2006) 40
Choice of bedding material by hamsters 411
versus wood pellets (the two ‘losers’).
Here, all hamsters began the experiment
with the same pairing: pine shavings versus
corn cob.
The position (cage) of each hamster, its
nest, its food, its latrine (accumulation of
urine) and its faeces was noted once a day,
during the light period of the light–dark
cycle. The number of running wheel
revolutions was also tallied daily. The days
that preceded and followed litter changes
were discarded, so that only 10 days of data
were used in the analysis. Depending on the
experiment and trial, 2–6 hamsters slept in
the tunnel on 1–4 days, and such data were
not used in the analysis.
All statistical tests were conducted with
SPSS for Windows. Significance level was set
at P ¼ 0.05.
Results
Few hamsters were found in the same cage
on all 10 days (Figures 1 and 2). If we define a
preference as being more than 50% of all
positions observed, then in the test of pine
versus aspen shavings (Figure 1a), eight out
of 13 hamsters preferred pine over aspen in
the first trial (P ¼ 0.2905 on a binomial test)
and 10 out of 13 in the second trial
(P ¼ 0.0461). In the first trial, three hamsters
transferred pine shavings into the aspen
shavings cage and made a nest out of it (the
volume transferred was not measured, but it
was sufficient to ensure that the body of the
sleeping hamster was only in contact with
that material). If we take this as a preference
for pine, then 12 out of 13 hamsters preferred
pine over aspen in the first trial (P ¼ 0.0017).
There were no transfers during the second
trial, and never any transfer of aspen
shavings.
In the test involving corn cob versus wood
pellets (Figure 1b), eight out of 13 hamsters
preferred corn cob in the first trial
(P ¼ 0.2905). This number rises to 10 out of
13 if transfers (all of which were of corn cob
into the wood pellet cage) are taken into
account (P ¼ 0.0461). In the second trial, 11
out of 13 (P ¼ 0.0112) preferred the corn cob;
this becomes 12 out of 13 if transfers are
taken into account (P ¼ 0.0017).
In the test involving pine shavings versus
corn cob (Figure 2a), eight out of 13 hamsters
preferred pine shavings in the first trial
(P ¼ 0.2905). This number rises to 10 out of
13 if transfers (all of which were of pine
shavings into the corn cob cage) are taken
Laboratory Animals (2006) 40
412 M Lanteigne & S G Reebs
0
25
50
75
100
12
Trial
12
Trial
% days in pine shavings
0
25
50
75
100
% days in corn cob
(a)
(b)
Figure 1 Percentage of days (out of a maximum of
10) spent by 13 hamsters on pine shavings versus
aspen shavings on two trials separated by 12 days
(a) and for corn cob versus wood pellets on two
more trials separated by 12 days (b). Open symbols
indicate animals that had transferred bedding from
one cage to the other (the data show the percen-
tage of days spent in the cage from which the
bedding was transferred, which still contained a
good portion of that bedding, and not the
percentage of days spent nesting on the bedding
irrespective of the cage where it was found). Some
data points were offset slightly to distinguish each
of the 13 lines
into account (P ¼ 0.0461). In the second trial,
eight out of 13 hamsters preferred the pine
shavings, but this becomes 13 out of 13 if
transfers (again, all of which were of pine
shavings) are taken into account
(P ¼ 0.0001).
In the test involving aspen shavings versus
wood pellets (Figure 2b), nine out of 13
(P ¼ 0.1334) and 12 out of 13 (P ¼ 0.0017)
hamsters preferred the aspen shavings in the
first and second trials, respectively. In both
trials, the numbers become 13 out of 13 if
transfers (all of which were of aspen shavings
into the pellets cage) are taken into account.
Food was always placed evenly between
the cages, be it at the beginning of the
experiment or during replenishments. Food
tended to remain present in all cages.
However, hamsters sometimes built food
piles in cage corners. For six of the eight
trials conducted in these two experiments,
there was no relationship between the
position of the biggest food pile and nest
position (w
2
tests, P varies between 0.071 and
0.747). However, for the two trials that made
the last cycle of the second experiment, the
biggest food pile and the nest tended to be in
the same cage (P ¼ 0.001 for each trial).
All hamsters used both of their wheels
fairly evenly. In none of the eight trials
conducted was there a significant difference
between the number of wheel revolutions in
the cage with the preferred bedding and the
number in the less preferred cage (paired
t-tests, P varies between 0.131 and 0.805,
n ¼ 13).
Discussion
In both experiments, results from the
second trial with a particular pairing were
consistent with those from the first. The
expressed preferences are therefore
replicable over a short period of time even
when experience with other types of bedding
material intervenes.
Preference was seldom absolute in the first
trial. Most hamsters slept and built nests in
both cages. Preference tended to be stronger
in the second trial: a preference criterion of
75% would have yielded much the same
results, in second trials, as did our less
restrictive criterion of 50%. This does not
mean, however, that the same preference
would continue to be expressed for the rest
of a hamster’s life. Only experiments lasting
over months could begin to address this
question.
Laboratory Animals (2006) 40
Choice of bedding material by hamsters 413
0
25
50
75
100
12
Trial
12
Trial
% days in pine shavings
0
25
50
75
100
% days in aspen shavings
(a)
(b)
Figure 2 Percentage of days (out of a maximum of
10) spent by 13 hamsters on pine shavings versus
corn cob on two trials separated by 12 days (a) and
for aspen shavings versus wood pellets on two
more trials separated by 12 days (b). Open symbols
indicate animals that had transferred bedding from
one cage to the other (the data show the percen-
tage of days spent in the cage from which the
bedding was transferred, which still contained a
good portion of that bedding, and not the percen-
tage of days spent nesting on the bedding irre-
spective of the cage where it was found). Some data
points were offset slightly to distinguish each of the
13 lines
No direct observations were made at
night, so that bedding material preference
can only be interpreted here in light of what
hamsters do during the day, which is for the
most part sleep. Given that hamsters in our
laboratory spend most of their time running
in wheels at night, the fact that both running
wheels were used equally suggests a lack of
bedding material preference related to night
activities (see Ras et al. 2002 for a similar
conclusion applied to rats).
In general, shavings were preferred over
granules (though we did not test aspen
shavings versus cor n cob). One possible
explanation for this result is that hamsters
chose the most stable and most comfortable
material to build nests for sleeping (see
Rajendram et al. 1987, Ago et al. 2002).
Granular material like pellets and corn
cob cannot be piled high in a shape that
surrounds the body of the sleeping hamster.
Indeed, the few nests we observed in the
cages with granular material were rather flat
and small, in contrast to the cup-shaped
nests made of shavings, a material that is
softer and more pliable. The fact that only
shavings were transferred between cages,
always to be used as nest material in the new
cage, supports the idea that hamsters chose
bedding materials primarily for their quality
for nest construction. Moreover, granular
material (especially the round cylinders
made by wood pellets, the least preferred of
the materials we tested) can roll underfoot
where the bedding layer has been thinned
and may have made walking uncomfortable.
This issue raises the question of whether
the preference for shavings would remain if
material better suited for nest building
(nesting material) were provided in addition
to the bedding material. This is addressed in
the next experiment.
Experiment II
Material and methods
Details were as in Experiment I, except that
the choice apparatus was made of four cages
linked by tunnels. The tunnels were of the
same dimensions as before, but now formed
a square with descending branches at each
corner, each branch giving access to a cage.
Each cage had food, water and a running
wheel, though the running wheels this time
were not connected to a computer and their
revolutions were not tallied. Each cage
contained a different bedding material (the
same four as in the previous experiment),
arranged in random order, and a partially
torn sheet of paper towel as nesting material
(see Van de Weerd et al. 1996, 1998). Litter
was changed every 10 days, at which time
new bedding and paper were provided in the
same cages.
Fourteen new male hamsters (60 days old,
from Charles River Canada) were each
placed in a different apparatus. The nature of
the bedding (cage) on which they were first
deposited was systematically varied between
individuals. For the next 31 days, the
position (cage) of each hamster and its nest
was noted daily. Notes were also made on a
daily basis of the presence of food, faeces and
urine in each cage. Running wheel activity
was not tallied.
Results
On average (n ¼ 14), hamsters were found in
their favourite cage on 20.4 out of 31 days,
and in their second favourite cage on 7.1 out
of 31 days. At the group level, no bedding
material was significantly preferred over
another (Table 1). Together, the two shaving
types were the first choice of only eight out
Laboratory Animals (2006) 40
414 M Lanteigne & S G Reebs
Table 1 Number of hamsters, out of 14, choosing a given material as their favourite or second favourite
bedding when nesting material (paper) is provided
Pine shavings Aspen shavings Corn cob Wood pellets w
2
test
Favourite 2 (23.0) 6 (18.0) 2 (22.5) 4 (21.2) w
2
=3.71, P>0.3
Second favourite 5 (7.0) 4 (6.25) 2 (8.0) 3 (8.0)
Numbers in parentheses show the mean number of days, out of 31, on which the hamsters who selected the bedding type were found on that
bedding
of 14 hamsters (P ¼ 0.3953). Two of the 14
hamsters preferred the bedding material on
which they had been placed at the beginning
of the experiment, a result not different from
random. Except for one hamster that slept
for three days in a nest of pine shavings
transferred onto wood pellets, there were no
transfers of bedding material from one cage
to another. Paper towels were used as nest
material by all hamsters.
As in Experiment I, food remained present
in all cages. Faeces were also present in all
cages, but were more abundant in the cage
where the nest was. Accumulation of urine
tended to appear in one corner of the cage
where the nest was.
Discussion
No significant preference for bedding type
was expressed among the hamsters. Even
within hamsters, preference was not
absolute, as only about two-thirds of all days
were spent on the favourite material. Thus
there seems to be little preference between
the bedding types if nesting material is
provided. These results support the
hypothesis that the preferences expressed
in Experiment I was caused by the relative
suitability and comfort of the bedding types
as nest material.
Preference mostly for comfort raises the
possibility that hamsters may choose
bedding material that, though suitable in
the short term for nest construction,
may be suboptimal in the long term for
health. In Experiment I, pine shavings were
preferred by most hamsters, yet casual
observations in our laboratory suggests that
bleeding of the feet occurs more often when
hamsters are housed on this bedding
material. Maybe shaving pieces get wedged
between the bars of the running wheels and
cut the paws, or various compounds in
pinewood soften the paws and make them
more prone to cuts and abrasions. In the
following experiment, we examined the
effect of pine shavings, aspen shavings and
corn cob on hamsters’ paw condition, weight
gain and running wheel activity over a
period of 50 days.
Experiment III
Material and methods
Thirty new male hamsters, 60 days old, were
purchased form Charles River Canada. Each
was placed in a single cage (Nalgene F-size
for rats). Each cage was equipped with a
running wheel (F-size for rats) connected to
a computer that tallied wheel revolutions
daily. Water and food were replenished
regularly as in the previous experiment. Ten
hamsters were on pine shavings, 10 on aspen
shavings and 10 on corn cob. The volume of
each bedding material was 1 L. Litter was
changed every 10 days over a period of 50
days.
Hamsters encounter wheels for the first
time of their life when they arrive in our
laboratory. They immediately start running
at high daily levels, and scabs often appear
on some of their feet. Every five days, the
hamsters were placed in a small transparent
box and their paws were examined. The total
number of scabs on all four feet was noted.
The severity of each scab was also noted,
according to the following scale: 1 ¼ small
black dot, 2 ¼ small healing white scab,
3 ¼ red scab, 0.5–1.5 mm in diameter, 4 ¼ red
scab larger than 1.5 mm. An overall scab
severity index was calculated for each
hamster by adding up the severity indices of
the scabs of all four paws. Every 10 days (at
the time of litter change) the hamsters were
weighed and the weight gain since the
beginning of the experiment was calculated.
The hamsters quickly got used to handling.
Running wheel revolutions were tallied as in
Experiment I, but equipment failure forced
us to discard 20 days worth of data for all
animals (the second and third 10-day blocks).
Repeated-measure ANOVAs (SPSS for
Windows) were used to compare the three
bedding treatments in ter ms of the total
number of scabs on the hamsters’ feet,
overall scab severity, body weight gain since
the beginning of the experiment and average
daily wheel revolutions. The repeated
measures were the data gathered every five
days for scabs, the data gathered every 10
days for weight, and the average daily wheel
revolutions for the 1st, 4th and 5th 10-day
blocks.
Laboratory Animals (2006) 40
Choice of bedding material by hamsters 415
To allow for the possibility that the
treatments might have affected hamsters
in the same way in the short run, but
differently in the long run, a one-way
ANOVA was conducted only on the data
gathered on the last day of the experiment
(or the last 10-day block in the case of wheel
running).
Paw condition and weight gain could be
affected by the amount of running wheel
activity. We therefore considered comparing
the three bedding treatments in an
ANCOVA that used running wheel activity
as a co-variable, with all variables averaged
for each animal over the 1st, 4th and 5th day
block (the 2nd and 3rd block were discarded
because of the lack of wheel running data
due to the equipment failure mentioned
above). However, only the pine shavings
group showed the expected correlations (less
weight gain and worse paw condition with
higher running levels), the two other groups
showing no significant correlations, and so
an ANCOVA was not appropriate.
Results
The three bedding treatments did not
significantly differ from one another in
terms of either the number of paw scabs per
animal (F ¼ 1.172, P ¼ 0.325), the overall scab
severity (F ¼ 1.188, P ¼ 0.320), weight gain
(F ¼ 1.083, P ¼ 0.353) and wheel running
(F ¼ 0.913, P ¼ 0.413) over the 50-day period
(Figure 3). Even if only the end of the
experiment is considered, there is still no
difference between the groups (scab number:
F ¼ 0.991, P ¼ 0.384; scab severity: F ¼ 0.573,
P ¼ 0.571; weight gain: F ¼ 0.902, P ¼ 0.417;
wheel running: F ¼ 2.818, P ¼ 0.077; note
that Figure 3 shows standard errors and not
standard deviations).
Discussion
The lack of detected differences raises the
question of whether the experiment lasted
long enough for any possible effect to
manifest itself. It must be pointed out that
paw condition was improving for all three
groups during the second part of the
experiment (Figure 3), which suggests that
any possible late effect would not be an
extensive one. Weight gain and running
activity also seemed normal for all three
groups, and so any possible late decline
would have to be precipitous to be
worrisome from a welfare point of view.
Nevertheless, we cannot discount the
possibility of various long-term effects not
detectable by our 50-day long experiment,
and therefore our conclusion – that bedding
material does not affect paw condition,
weight gain and wheel running activity in
hamsters – is of practical interest only in
situations where hamsters are kept in
captivity for a maximum of a few months.
Laboratory Animals (2006) 40
416 M Lanteigne & S G Reebs
0
0.4
0.8
1.2
1.6
2
5 101520253035404550
5 101520253035404550
5 101520253035404550
5 101520253035404550
number of scabs
pine
aspen
corn cob
0
1
2
3
4
5
overall scab severity
0
10
20
30
40
50
weight gain (g)
0
2000
4000
6000
8000
10000
12000
day
daily wheel
revolutions
(a)
(b)
(c)
(d)
Figure 3 Evolution of various parameters (means
þ standard error, n ¼ 10) in hamsters housed with
different bedding materials over a 50-day period
As for all negative conclusions,
considerations of statistical power must be
addressed. Perhaps our sample size and
statistical test were not sufficient to detect a
small effect. If so, it must be pointed out that
the tendency shown in Figure 3 is for a
beneficial effect of pine shavings (more
weight gain and better paw condition), a
result that is consistent with the preference
exhibited in Experiment I, but not with our
original expectation based either on previous
experience or on some reservations
expressed in the pet care literature
(e.g. Alderton 2002, Bucsis & Somerville
2002) about the suitability of resinous (cedar
or pine) shavings as bedding material for
hamsters. Any small effect that followed
the trends of Figure 3 would therefore be
difficult to interpret.
General discussion
Choice tests like those we used in this study
only give relative preference between
alternatives, so a non-preferred bedding
material is not tantamount to a disliked or
inappropriate material (Duncan 1992). Most
hamsters spent at least some of their
sleeping time on their least preferred
material (Figures 1 and 2), indicating that
none of the tested materials was strictly
unacceptable.
In the absence of nesting material, pine
shavings were the preferred bedding
material. Pine shavings were also the
cheapest of the four alternatives we tested.
Over 50 days, pine shavings did not
significantly affect paw condition and body
weight relative to the other materials, but
longer experiments with higher sample sizes
are necessary to confirm this preliminary
result. Such experiments should also test
females as well as males, as in Reebs and
St-Onge (2005).
The most straightforward conclusion from
our study is that hamsters, in the short term,
seem to prefer bedding material that is
suitable for nest construction. When specific
nesting material is provided, there appears to
be little preference for one type of bedding
material over another. Bedding materials
may still differ in other ways than comfort,
for example in terms of waste absorbency or
their capacity to sustain bacteria, but any
adverse effects this might cause is likely to
be minimized, perhaps to negligible levels,
by regular replacement of the litter. Thus,
in standard conditions of animal care
(i.e. regular litter replacement), and with
nesting material being provided, we cannot
as yet recommend one bedding material over
another among the four types we tested.
Another conclusion that rises from our
results is that hamsters exhibit a strong
tendency towards nest building, even at
room temperature. Nesting material should
always be provided for this species, either in
a form suited specifically to that use, or in
the form of a bedding type that can double as
nesting material, such as shavings.
Acknowledgements We thank Darren MacKinnon
for help with the care of the hamsters. This research
was primarily supported by a grant to SGR from the
Faculte
´
des E
´
tudes Supe
´
rieure et de la Recherche de
l’Universite
´
de Moncton. The Natural Sciences and
Engineering Research Council of Canada also
contributed through a Discovery Grant to SGR and an
Undergraduate Summer Research Award to ML.
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