Effects of Muzzling
G. M. Cronin, , a, P. H. Hemswortha, b, J. L. Barnetta, E. C. Jongmana, E. A. Newmana and
I. McCauleyc
a Animal Welfare Centre, Department of Primary Industries, Victorian Institute of Animal
Science, 600 Sneydes Road, Werribee 3030, Vic., Australia
b Animal Welfare Centre, University of Melbourne, Institute of Land and Food Resources,
Parkville 3010, Vic., Australia
c Department of Growth and Development, Department of Primary Industries, Victorian
Institute of Animal Science, Mickleham Road, Attwood 3049, Vic., Australia
Accepted 23 May 2003. ; Available online 6 August 2003.
Abstract
A commercial anti-barking muzzle for dogs was tested during winter on Australian Kelpies
at a commercial breeding kennel, to examine the effects of the device on dog behaviour
and welfare. The trial involved 16 dogs (paired on sex and age); one dog per pair was
allocated at random to the Muzzle Treatment (MT) and the other to the Control
Treatment (CT) (not muzzled). The dogs were penned individually with pairs housed in
adjacent pens. Muzzle Treatment dogs wore the anti-barking device for about 43 h.
Muzzles were removed for about 30 min on day 2 of the treatment period while dogs were
fed. The behavioural responses of dogs were recorded over 4 days, from before
application of muzzles (pre-treatment) to 2 days after removal of the muzzles (post-
treatment period). Saliva samples were collected at 2, 21 and 24 h post-muzzling to
measure saliva cortisol concentrations.
The initial response of dogs to wearing muzzles was to display submissive behaviour: tail
held between the hind legs or down for the first few minutes only and head and tail down
for the majority of time while wearing the muzzles, especially in the absence of humans.
Activity level (2.3 versus 15.7% of observations), barking (0.1 versus 7.8%) and standing
posture (8.3 versus 29.5%) by dogs were significantly reduced (P<0.05) while wearing the
muzzles compared to non-muzzled controls. Even in response to stimulation from
humans, dogs barked significantly less when muzzled compared to non-muzzled controls
(0.5 versus 23.4% of observations, P<0.01). However, based on saliva cortisol
concentrations there was no evidence of a physiological stress response to wearing the
muzzles. After removal of the muzzles after 43 h of treatment, the dogs in the Muzzle
compared to Control Treatment tended to stand more (P<0.06) during observation
sessions over the next 2 days (48.3 versus 32.5% of observations). It was concluded that
although dogs responded to wearing the muzzle by modifying their behaviour, including
the display of submissive behaviour, and vocalisation, there was no indication that the
dogs showed a stress response when wearing the muzzle. Further evaluation of anti-
barking muzzles for dogs is recommended to test the ability of dogs to drink and pant
while wearing the device during hot weather, to ensure they can effectively
thermoregulate.
Author Keywords: Dog; Behaviour; Stress; Welfare; Muzzle; Barking; Vocalisation
Article Outline
1. Introduction
2. Materials and methods
2.1. Housing
2.2. Treatments
2.2.1. Behaviour observations—Experiment 1
2.2.2. Cortisol measurements—Experiment 2
2.3. Statistical analysis
3. Results
3.1. Initial reactions of dogs to wearing the muzzle from the video records
3.2. Barking by dogs
3.2.1. Barking response to the stimulus human
3.2.2. Barking during non-stimulation periods
3.3. Postures and activity level of dogs
3.3.1. Standing posture
3.3.2. Lying posture
3.3.3. Sitting posture
3.3.4. Activity
3.4. Lacerations
3.5. Cortisol concentrations
3.6. Barking amongst “debarked” and non-debarked dogs
4. Discussion
5. Conclusion
Acknowledgements
References
1. Introduction
Sixty-six percent of the 6 million Australian households have at least one pet and 40% of
these pets are dogs. However, dogs in the general community can cause embarrassment
and inconvenience to their owners. Excessive barking by dogs, for example, is a
considerable social problem ([Kobelt et al., 2003]) often with extreme solutions, such as
surgical “debarking” or euthanasia. “Anti-barking” muzzles may offer a solution to this
problem. The device used in this trial was a commercial anti-barking muzzle which was
made of elastic and cloth and designed to allow the dog to feed and drink while wearing it.
The device was designed to impose pressure on the jaws of a barking dog and thereby tire
the jaw muscles and inhibit barking. Two experiments were conducted to evaluate the
welfare implications of the device’s effects on the dog.
There are a number of ways in which the device could be used. However, it is most likely
that at least initially such a device, if effective in reducing barking, would be valuable to
dog owners who have animals that incessantly bark when family members are absent or
during the evening. In such situations the device may be applied during the period in
which the barking is expected, for example, during the day when the owner(s) is absent or
during the evening when people are sleeping. The present experiments did not examine
the effectiveness of the device as a training aid, but examined the most pressing issue:
examining its effectiveness when the muzzle is worn for long periods, i.e. for those
situations in which barking is expected. In such situations, it is important that the welfare
of the dog is not seriously compromised. Thus, in the following experiments the device
was tested when worn over about 2 days by dogs, some of which had a history of
uncontrollable barking, in situations in which barking was stimulated. While this use was
atypical, it was chosen on the basis that if problems were not to arise in this scenario, they
would be unlikely to arise if the device was to be used for shorter periods.
There has been disagreement over what is important for the welfare of animals and this
has led to attempts to study and conceptualise animal welfare in more scientific ways
([Duncan and Fraser, 1997]). The most recognised approach within scientific circles in
assessing risks to the welfare of animals involves studying whether the animal’s biological
systems are functioning in a normal or satisfactory manner. This approach, which is often
called the “functioning-based” approach ( [Duncan and Fraser, 1997]) or the
“homeostasis” approach ( [Barnett et al., 2001]), is underpinned by the definition that “the
welfare of an individual is its state as regards its attempts to cope with its environment” (
[Broom, 1986]). While there are some limitations to this approach, this approach has the
most scientific credibility and has been used by many scientists to assess welfare (
[Hemsworth and Coleman, 1998]).
There are examples in the literature of examining short-term challenges to animals using
this approach. [Lay et al., 1992] studied the behavioural and physiological responses of
cattle to two branding procedures to assess the relative aversiveness of the procedures.
[Hemsworth et al., 1996] utilised behavioural and physiological responses together with
growth performance to assess the welfare implications of a husbandry procedure regularly
imposed (daily injections) on pigs. [Ogburn et al., 1998] measured behaviour and some
physiological responses including cortisol concentrations, heart rate and blood pressure
in dogs to compare the effects of neck and head collars. In the present experiments we
examined the risks to welfare of dogs of wearing the an anti-barking muzzle, utilising the
functioning-based or homeostasis approach, in which behaviours indicative of
maladaption and an element of the stress response were measured.
2. Materials and methods
Two experiments were conducted at a commercial dog breeding kennel, about 100 km
west of Melbourne in central Victoria, involving a total of 16 Australian Kelpies. All dogs
except one (in the Muzzle treatment (MT)) had been trained and displayed at dog shows.
The experiments were each conducted in two time replicates (weeks) with eight dogs per
replicate. Due to difficulties in assaying the saliva samples from experiment 1, this aspect
of the experiment was repeated. The repeated experiment (experiment 2) involved the
same 16 dogs.
2.1. Housing
During the two experiments the dogs were individually housed in a row of adjacent pens
measuring 1.5 m×4.0 m. Pens consisted of two compartments: a 1 m long indoor
compartment at the rear of the pen and a 3 m long outdoor run. The indoor compartment
was solid brick construction with concrete floor and was separated from the outdoor run
by a partial brick wall to the height of the roof and a solid door. Access to the indoor run
was available over-night between about 18:00 h and 08:00 h. The solid roof extended 1 m
into the outdoor run, while the other 2 m was covered with shade cloth. The front and side
fences of the outdoor run were made from 40 mm×40 mm mesh galvanised wire panels. A
wire mesh gate was situated in the front fence of the pen and the floor of the pens sloped
towards the front. Each pen contained two dog beds made of fabric on metal frames
(indoor and outdoor) and a water bowl. Dogs were fed each morning between 08:00 and
08:45 h when the pens were also cleaned. Dogs were allowed to leave their pen during
cleaning when they had unrestricted access to a large forest area in front of the dog
kennels. However, only one dog at a time was allowed out of the pens.
2.2. Treatments
Dogs were selected from available adult subjects prior to experiment 1. The dogs were
paired on same sex and similar age basis (mean age 45 months, range 4–92 months) and
moved to a pen on day 1, following allocation to pens within pairs at random. Thus, the
pairs of dogs were housed in adjacent pens with one dog per pair allotted to the Muzzle and
the other to the Control Treatment (CT). Two of the eight subjects in the Muzzle and five
of the eight in the Control Treatment had been surgically “debarked” (D) more than a year
prior to the experiments, because of noise issues. This procedure removes all or part of
the vocal chords and had been performed to reduce the loudness of barking. As described
by [Houpt and Wolski, 1982], dogs are not rendered silent by this procedure, but the
strength and pitch of their voices are lowered. The same dogs were used in experiment 2,
but dogs in the Muzzle Treatment in experiment 1 were used as Control Treatment
subjects in experiment 2 and vice versa. There were two treatments:
Muzzle treatment: at about 12:00 h on day 4, an experimenter entered the dog’s pen and
fitted the appropriate-sized “Husher” anti-barking muzzle to the dog. The muzzle
consisted of black elastic material which encircled the dog’s snout, edged with webbing
which limited expansion of the elastic. Two pieces of webbing extended from the muzzle to
form a neck strap, which could be pulled tight and locked at the back of the dog’s head,
making it difficult for the dog to dislodge the muzzle. Muzzles were removed for about 30
min at feed time (about 08:00 h) on day 5 and were removed but not replaced at feed time
on day 6 in experiment 1. In addition, the muzzles were briefly removed to facilitate
collection of saliva samples for cortisol assay at 2, 21 and 24 h after the initial muzzling
and were replaced within 2 min. This protocol was repeated for experiment 2, although in
experiment 2 muzzles were not replaced on the dogs following the third saliva sample, i.e.
24 h post-muzzling, since we were not collecting behaviour data. Thus in experiment 1,
Muzzle Treatment dogs wore the anti-barking muzzle for about 42.5 h, while in
experiment 2, dogs wore the muzzle for 24 h.
Control treatment: at about 12:00 h on day 4, and at the same time as for the paired-dog in
the Muzzle Treatment, an experimenter entered the pen and handled the dog in a manner
similar to the Muzzle Treatment, but without fitting the dog with a muzzle. Control
Treatment dogs were also handled in a similar manner and at the same times as the Muzzle
Treatment dogs for feeding and collection of saliva samples.
All dogs were examined each day by the owner during the feeding and cleaning routine, for
injuries, such as lacerations on the head.
2.2.1. Behaviour observations—Experiment 1
Direct behaviour observations were conducted on the eight dogs per replicate from days
4–7, with observation sessions commencing at 09:00, 10:00, 12:00 and 13:00 h. About 2
min prior to commencing an observation session, the observers (four on days 4 and 5 and
two on days 6 and 7) sat in a chair positioned about 2 m from the front of the pens,
opposite a pair of focal dogs (i.e. one from the Muzzle and the other from the Control
Treatment). Each observation session was sub-divided into four 10.5 min behaviour
recording periods, which commenced with a 30 s “barking response to human stimulation”
test, in which a human walked along the front of the pens, from one end to the other then
back, to “stimulate” the dogs to bark. The observers recorded whether either of their two
dogs barked during the 30 s stimulation. At the conclusion of the 30 s stimulation, the
observers then commenced recording the behaviour of the dogs, one subject at a time for
30 s, alternating between dogs in each successive 30 s period for the next 10 min. The dog
observed first in each period was alternated so that in each observation session, each dog
was observed first twice out of the four periods. At the end of the first, second and third
behaviour recording period per session, the human stimulus again walked back and forth
along the front of the pens, to stimulate the dogs. In an attempt to provide variation in the
stimulus, the human stimulus moved/behaved/vocalised in a different manner each time,
or incorporated a different object of potential interest to the dogs, such as a ball, bucket,
stick, etc. Observers rotated places between observation sessions and the human stimulus
was different in each session on any day. The exception to this protocol was the initial
period when the Muzzle and Control Treatments were applied. In this period (i.e. the 12:
00 h observation period on day 4) the stimulus human did not walk in front of the dogs
because the imposition of the treatments was, by necessity, staggered by a minute or so
between pairs of dogs.
In each 30 s behaviour observation period, the observer recorded the predominant
(defined as occurring during at least half of the time) posture of the dog (stand, sit or lie),
whether the dog was predominantly active (moving about in its pen) or inactive, and
whether the dog barked, drank water, pawed at its head/muzzle or rubbed its head/muzzle
against a surface or object in the pen. In addition, four video cameras were mounted in the
kennels to provide a continuous record of the behaviour of all eight dogs per replicate.
The cameras were connected to time-lapse video recorders.
2.2.2. Cortisol measurements—Experiment 2
Saliva samples were collected from the 16 dogs at 2, 21 and 24 h after the application of
the muzzles. Experiment 2 was conducted using the same protocol as experiment 1, with
the exceptions that (1) dog behaviour was not recorded and two instead of four human
observers sat opposite the pens to simulate behaviour recording and (2) the experiment
was completed on day 5, 24 h after the application of the treatment.
To collect the saliva sample, two experimenters entered the dog’s pen. One person held
the dog while the other removed the muzzle (in the Muzzle Treatment). The flow of saliva
was stimulated by allowing the dog to chew a plug of cotton wool impregnated with
crystallised citric acid (5% solution). Saliva was collected in balls of cotton wool, which
were then sealed in cling film, transferred to a screw-top vial and placed on ice. The
samples were then transported to the laboratory and the saliva was extracted from the
cotton wool using a centrifuge and stored at about −20 °C until assayed. After thawing,
saliva samples were centrifuged at 12 000 rpm in a microcentrifuge to precipitate any
particulate matter. A 250 μl aliquot was extracted with 2.5 ml of dichloromethane on an
orbital shaker for 15 min. A 2.0 ml aliquot of the organic phase was removed and allowed
to dry down overnight. The dried extract was resuspended by vortex mixing following the
addition of 200 μl of 0.1 M tris-buffered saline, pH 7.4, containing 0.1% bovine gamma
globulin. This was split into two 100 μl aliquots and analysed by a commercial RIA kit for
cortisol (Orion Diagnostica, Turku, Finland) according to the protocol for salivary
samples. The within- and between-assay coefficients of variation for cortisol
concentrations of 3.4 and 13.3 nmol/l were 11 and 7% (within-) and 17 and 10% (between-
), respectively.
2.3. Statistical analysis
The behaviour data were collated into three time periods categorised according to
treatment situations: (1) pre-treatment, (2) treatment and (3) post-treatment. The pre-
treatment period included the data recorded in the observation sessions that commenced
at 09:00 h and 10:00 h on day 4. The treatment period was comprised of the 12:00 h and
13:00 h sessions on day 4, together with the 09:00, 10:00, 12:00 and 13:00 h sessions on
day 5. The post-treatment period consisted of all observation sessions on days 6 and 7.
Differences in the vocalisation, behaviour and posture of dogs between the Muzzle and
Control treatments were analysed within time periods using the Kruskall–Wallis one-way
analysis of variance with the χ2 approximation to provide information on the level of
significance ([GenStat, 2000]). The occurrence of barking by “debarked” and “intact” (I)
dogs was also compared within time periods using the Kruskall–Wallis one-way analysis of
variance and the χ2 approximation. A post-hoc comparison of the interaction between the
treatments and surgical “debark” status of dogs was not possible due to an unbalanced
data set. Values reported are raw mean percentages. Cortisol data were analysed using
analysis of variance blocked on replicate and pairs of dogs.
3. Results
3.1. Initial reactions of dogs to wearing the muzzle from the video records
Muzzling resulted in four of the eight Muzzle Treatment dogs almost immediately lowering
their tail between the legs, although their tails were only held in this position for less than
30 s. The predominant tail position for all eight muzzled dogs over the first 15 min of
wearing the muzzle was “down” compared to “raised”. In addition, there were very few
instances of tail wagging over the 15 min. Initially, the dogs’ ears tended to be “back” but
within 1 min of being muzzled, ears reverted to the usual, upright position. Scans of the
entire time-lapse video record indicated that dogs while standing, also generally tended to
keep their heads and tails lowered while muzzled, i.e. over the entire 43 h period,
particularly in the absence of humans.
During the first 30 s of being muzzled, seven of the eight dogs pawed at the muzzle and six
dogs rubbed their head against a surface, such as the floor or mesh walls of the pen. The
video record also showed that during the first 15 min of being muzzled, on average dogs
performed about five bouts of pawing at the muzzle and four bouts of rubbing their head.
These behaviours were not apparent 24 h later. All Muzzle Treatment dogs displayed
bouts of inactivity, either standing, sitting or lying on the sternum stretched out.
3.2. Barking by dogs
3.2.1. Barking response to the stimulus human
Table 1 shows the proportion of tests that dogs in the two treatments barked at the
stimulus human, before application, during wearing and following removal of, the anti-
barking muzzle. While there was no difference between the treatments in the occurrence
of dogs barking at the stimulus human in the pre-treatment period (P>0.05), Muzzle
compared to Control Treatment dogs barked significantly less (P=0.002) when wearing
the anti-barking muzzle in response to the stimulus human during the treatment period. In
the post-treatment period after removal of the muzzles, there was no difference in the
incidence of barking in response to human stimulation (Table 1).
Table 1. Mean proportion of observations in which dogs in the Muzzle and Control
Treatments vocalised, occupied different postures and were active during the experiment
Values shown are raw mean percentages. Data were analysed using the Kruskall–Wallis
one-way ANOVA and the χ2 approximation. Within time periods, the asterisk indicates
significant difference between the treatments.
3.2.2. Barking during non-stimulation periods
There was no difference (P>0.05) due to treatment in the pre-treatment period in the
incidence of “free” barking by dogs during the observation periods (Table 1), as distinct
from the 30 s of human stimulation at the start of each observation period. However,
Muzzle Treatment dogs barked significantly less (P=0.003) than Control Treatment dogs
during the treatment period (Table 1). In the post-treatment period there was no effect
(P>0.05) of treatment.
3.3. Postures and activity level of dogs
3.3.1. Standing posture
While the Muzzle Treatment tended (P=0.14) to spend more time standing than the
Control Treatment during observations in the pre-treatment period, the difference was
not significant (Table 1). However, dogs spent less (P=0.024) time standing during the
treatment period in the Muzzle than Control Treatment (Table 1). Following the
permanent removal of muzzles from dogs in the Muzzle Treatment, there was a trend for
the Muzzle Treatment to stand more compared to the Control Treatment (P=0.059).
3.3.2. Lying posture
Lying was the most common posture recorded for dogs in the experiment. There was no
difference due to treatment in time spent lying in the pre-treatment period (P>0.05), but
there were effects after the dogs were muzzled. In the treatment period, the Muzzle
compared to Control Treatment, respectively, spent 84 and 55% of observation time lying
(P=0.027). Following the removal of the muzzles in the post-treatment period, there was a
weak (P=0.014) effect of treatment on time spent lying (Table 1).
3.3.3. Sitting posture
Sitting was the least common posture measured. There were no effects of treatment on the
occurrence of sitting posture in any of the three treatment periods (Table 1).
3.3.4. Activity
The level of activity of dogs was measured by the proportion of 30 s periods in which the
dog spent at least 15 s ‘moving about’ the pen. While there was no effect of treatment on
activity level in the pre-treatment period (P>0.05), the application of the muzzle resulted
in a significant reduction in activity compared to the Control Treatment dogs (P=0.005;
Table 1). In the post-treatment period, Muzzle Treatment dogs were more active than
Control Treatment dogs, but the difference was not significant (P>0.05; Table 1).
3.4. Lacerations
The owner of the dogs performed inspections of the dogs during and after the muzzles
were worn by the dogs and found no evidence of lacerations. During observations and on
the video record, while we noted that dogs pawed at the muzzle or rubbed the head/muzzle
against objects, these behaviours did not apparently result in physical damage to the dogs.
3.5. Cortisol concentrations
There were no effects of treatment on free cortisol concentrations of dogs at either 2, 21
or 24 h after the application of the anti-barking muzzles. The pooled mean (±S.D.)
concentrations for dogs in the two treatments over the three sample periods were 2.79
(±0.93), 2.34 (±0.80) and 2.22 (±0.55) nmol/l, respectively. The mean treatment
concentrations at 2 h post-application of the muzzling/sham-handling were 2.66 (±1.11)
and 2.92 (±0.76) nmol/l, respectively, for the Muzzle and Control Treatments, and at 24 h
post-application were 2.14 (±0.40) and 2.30 (±0.69) nmol/l, respectively.
3.6. Barking amongst “debarked” and non-debarked dogs
Surgically “debarked” dogs differed from dogs with “intact” vocal chords in the
occurrence of barking recorded in the pre-treatment and treatment periods. In response
to human stimulation in the pre-treatment period, the “debarked” dogs barked more than
the “intact” dogs (64.3 versus 22.2% of observations, respectively, P=0.029) and there
was a tendency (P=0.069) for more “free” barking during observation periods (19.6
versus 4.3%, respectively). Similarly, during the treatment period “debarked” dogs
vocalised more in response to human stimulation (24.2 versus 2.4%; P=0.031) and
performed more “free” barking (7.2 versus 1.4%; P=0.047) than “intact” dogs. However,
there were no differences in these parameters in the post-treatment period. Table 2 shows
the mean data for barking by “debarked” and “intact” dogs in the different treatments,
over the three time periods. The data indicate that on average, there was a relative
increase in barking in response to human stimulation by Muzzle compared to Control
Treatment dogs between the pre- and post-treatment periods.
Table 2. The occurrence of barking by “debarked” (D) and “intact” (I) dogs in the Muzzle
(MT) and Control Treatments (CT) during the pre-treatment, treatment and post-
treatment periods
Values shown are mean percentage of observations.
4. Discussion
The anti-barking device significantly reduced the occurrence of barking by dogs. While
the changes to activity level and standing posture recorded for dogs wearing the muzzle
were relatively large compared to the pre-treatment period and the Control Treatment,
there were no apparent adverse effects of wearing the muzzle, for example, on self-
damaging behaviours, lacerations or saliva cortisol response.
The measurements on saliva cortisol taken during these experiments provide no evidence
of a substantial activation of the hypothalamic–pituitary–adrenal axis. If the muzzle
caused a serious challenge to the animal, a significant cortisol increase would be expected.
The primary saliva samples were collected 2 h post-muzzling. While it is possible the dogs
experienced an acute stress response to muzzling or sham-handling, the elevation in
cortisol concentrations was not present after 2 h. The lack of treatment differences cannot
be explained in terms of human contact confounding treatment effects. Saliva samples
were generally taken within 2 min of entering the dogs’ pens and this interval is likely to be
insufficient for plasma cortisol concentrations to have been affected by the handling
associated with collection ([Broom and Johnson, 1993]). Since the dogs had one more
week of regular exposure to the observers prior to experiment 2 in which samples were
collected, the novelty of the presence of observers is unlikely to have masked treatment
effects.
There was no evidence of behavioural responses to the treatment that were indicative of
sustained avoidance, such as vigorous or unusual movements that may occur when an
animal is confronted with a serious challenge. Most dogs attempted to remove the muzzle
by pawing or rubbing, which could be considered natural responses of dogs to disengage
themselves from the muzzle, however, this response was only observed within the first 15
min of the muzzle being applied. There was no evidence of injury around the snout/muzzle
area and, based on the behavioural observations, no such effect was expected.
Following initial attempts to remove the muzzle, the activity of the dogs as measured by
the occurrence of standing posture and ambulation, was significantly reduced while
wearing the muzzle. This reduction in activity may be due to several reasons. The
application of the device may cause subordination through forcing the mouth closed,
inhibiting the display of the teeth which are the dog’s “weapons”, or inhibiting movement
([Schenkel, 1967]). Indeed the initial behavioural response of most dogs upon muzzling
included holding the tail between the legs or down and inactivity. [Schenkel, 1967] and
[Ogburn et al., 1998] describe these as submissive behaviours, although it is also possible
that dogs were reacting to the novelty of wearing a muzzle. [Schenkel, 1967] also
described dominant behaviour in the situation of a superior dog seizes the inferior’s
muzzle while uttering a growl. The anti-barking muzzle may be interpreted by the wearer
as being mouthed by a dominant.
Mild but repeated stimulation to the muzzle region of the dog may also cause inactivity,
however, such stimulation if causing disturbance or irritation is generally associated with
excessive rubbing ([Broom and Johnson, 1993]). The novelty of the restraint of the mouth
may also cause inactivity. However, while novelty will cause an initial orienting response (
[McFarland, 1981]) which may involve inactivity, if habituation does not occur, on-going
activation of the hypothalamic–pituitary–adrenal axis, with increased release of cortisol,
in response to the stimulus would be expected ( [Hemsworth and Coleman, 1998]).
The apparent “rebound” in standing posture, activity and vocalisation post-treatment, as
suggested in Table 1 and Table 2, is an interesting phenomenon. While it may be
interpreted as evidence of a serious suppression in motivation, the rebound may reflect an
increase in normal (ambulatory) activity after a period of exposure to a novel stimulus
and associated inactivity. The increase in activity following removal of the muzzle may be
due to lack of exercise while muzzled, with dogs potentially compensating for a lower than
normal level of exercise in their activity budget while muzzled. In rats, [Mueller et al.,
1999] found that wheel-running increased after 3 h deprivation and was proportional to
the amount of running normally occurring during the deprivation period. Thus, the
increase in activity of the Muzzle treatment dogs following removal of the muzzles may be
explained as compensating for their recent lack of exercise, although a longer period of
observation post-treatment may be required to provide conclusive evidence. The
increased activity may also be associated with dogs attempting to regain their social status
if the muzzle acted to cause subordination. It should also be recognised that while some
authors have suggested that heightened activity after a period of deprivation may result
from an increase in motivation during deprivation and hence may be considered as
potentially indicative of suffering ([Metz and Wierenga, 1984]), the basis and indeed the
welfare implications of such rebound effects are far from clear. [McFarland, 1989] has
suggested that animals may habituate to the presence of a stimulus and not notice its
subsequent removal or absence. But on later presentations of the stimulus, they may show
an exaggerated behavioural response because of renewed novelty. Thus, it is difficult to
speculate on the welfare implications of the rebound effect. If the muzzle was causing a
serious challenge for the animal, some substantial and prolonged behavioural and
physiological responses would be expected. While reduced activity was apparent, there
was no evidence of major biological responses.
Not unexpectedly, the surgically “debarked” dogs vocalised more than the non-debarked
dogs. The noises made by these dogs could be described as hoarse barks. Thus while
“debarking”, which had occurred more than 12 months prior to these experiments for 7 of
the dogs, did not stop the dogs vocalising, we do not know whether “debarking” alters their
motivation to bark.
5. Conclusion
While dogs showed a reduction in activity including barking when wearing the anti-
barking device, there were no significant changes in behaviours that were indicative of a
painful or aversive stimulus, such as sustained, vigorous attempts to remove the stimulus.
Furthermore, there were no significant changes in saliva cortisol concentrations.
However, the environmental conditions under which the experiments were conducted
were limited. One obvious area of potential concern and need for further research is any
welfare risk during periods of hot and/or humid weather.
Acknowledgements
This research was conducted with funding provided by the Animal Welfare Centre,
Werribee. We are extremely grateful to Ms. Joy Wangler who allowed us to use her dogs
and kennel facilities for the research. Thanks also to the many staff who willingly helped
with the collection, collation and analysis of the data, including S. Dowling, E. Leeson, E.
Selby and Dr. K. Stagoll. The statistical advice and assistance of Mr. K.L. Butler in
analysing the data are acknowledged.
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Applied Animal Behaviour Science
Volume 83, Issue 3, 26 September 2003, Pages 215-226
| An anti-barking muzzle for dogs and its short-term effects on behaviour and saliva cortisol concentrations |