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Evaluation of plasma cortisol levels and behavior in
dogs wearing bark control collars
Janet E. Steiss
a,
*, Caroline Schaffer
b
, Hafiz A. Ahmad
c
,
Victoria L. Voith
d
a
Department of Biomedical Sciences, College of Veterinary Medicine, Nursing & Allied Health,
Tuskegee University, Tuskegee, AL 36088, USA
b
Center for Human–Animal Interdependent Relationships, College of Veterinary Medicine,
Nursing & Allied Health, Tuskegee University, Tuskegee, AL 36088, USA
c
Center for Computational Epidemiology, Bioinformatics & Risk Analysis,
College of Veterinary Medicine, Nursing & Allied Health, Tuskegee University,
Tuskegee, AL 36088, USA
d
College of Veterinary Medicine, Western University of Health Sciences, Pomona, CA, USA
Accepted 29 June 2006
Available online 8 August 2006
Abstract
On wk 1, 24 healthy mixed breed kennel dogs were screened by physical examination, complete blood
count, serum biochemistry, and plasma cortisol measurement. Dogs were tested to ensure they barked at an
unfamiliar dog. Dogs were randomly assigned to control, electronic bark collar or lemon spray bark collar
groups (n= 8 per group). On wk 0 (acclimation baseline), dogs wore inactivated collars 30 min/day for 3
consecutive days. On wks 1 and 2, dogs wore an activated collar 30 min/day for 3 consecutive days. Controls
wore an inactivated collar. The bark stimulus was an unfamiliar dog walked in front of the run, three times,
30 s per presentation. Plasma cortisol was measured wk 1, wk 0 d 3, wk 1 d 1, wk 1 d 3 and wk 2 d 3. ACTH
was measured wk 0 d 3 and wk 1 d 1. Barking and activity were measured each session.
Results: Dogs wearing electronic or lemon spray collars barked less than controls (P<0.05) by the 2nd day
wearing an activated collar, with no significant difference in barking between collars. Mean numbers of
collar corrections per dog on the 1st day wearing an activated collar were 4.0 (electronic) and 2.0 (lemon
spray); the values decreased to 0 for both collars on the 3rd day. ACTH levels did not differ among groups
(P>0.05). Mean plasma cortisol levels were within the reference range for all groups throughout the study.
Overall, there was a significant time effect (P<0.05) but no significant difference in plasma cortisol
between the control, lemon spray and electronic collar groups (P>0.05). Activity did not change
significantly over time (P>0.05).
www.elsevier.com/locate/applanim
Applied Animal Behaviour Science 106 (2007) 96–106
* Corresponding author at: Department of Anatomy, Physiology & Pharmacology, College of Veterinary Medicine,
Auburn University, Alabama 36849, USA. Tel.: +1 334 844 8505; fax: +1 334 844 4542.
E-mail addresses: steisje@auburn.edu,steisje@vetmed.auburn.edu (J.E. Steiss).
0168-1591/$ – see front matter #2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.applanim.2006.06.018
Conclusion: Electronic and lemon spray bark collars significantly reduced barking, with no significant
difference between collar types. Dogs with either type of bark collar had an increase in plasma cortisol the
1st day wearing the activated collar, but this was not statistically significant (P>0.05). There was no
statistically significant difference in plasma cortisol levels between dogs wearing control, lemon spray or
electronic collars.
#2006 Elsevier B.V. All rights reserved.
Keywords: Dog; Bark collar; Cortisol; Scent collar; Barking; Welfare
1. Introduction
Dog owners in the USA and United Kingdom who have been surveyed regarding canine
behavior problems have typically listed excessive barking as one of the most common complaints
(Beaver, 1994; Campbell, 1986; Wells and Hepper, 2000). When Patronek et al. (1996)
conducted a case–control study of households that relinquished dogs for adoption, they found
that if the work of caring for a dog was more than expected, then the dog was at increased risk of
relinquishment. Unwanted barking was one of the factors which significantly contributed to care
of the dog being more than expected. Recently, Villalobos (2005) pointed out that responsible pet
ownership includes controlling excessive barking, and that veterinarians have a consultant role to
guide pet owners who need help with this problem.
Anti-bark collars such as electronic (‘‘shock’’) collars have been considered effective bark
deterrents (Hart and Hart, 1985), but some owners have concerns that these collars may inflict
undue pain and stress (Rudolph and Myers, 2004). Citronella spray collars are an alternative.
Studies comparing electronic and spray collars have indicated that citronella spray collars (Juarbe-
Diaz and Houpt, 1996; Moffat et al., 2003) and unscented spray collars (Beaudet, 2001) also deter
barking. Moffat et al. (2003) compared citronella and unscented spray collars. Both collars reduced
barking, but there was a trend toward higher efficacy with the citronella spray collar.
Some authors have suggested that a citronella spray collar may be gentler and more effective than
an electronic collar (Rudolph and Myers, 2004). The mechanism of action of the citronella spray
collar is not known. Collar mounted training devices marketed to suppress barking are designed to
deliver an aversive stimulus immediately, reliably, and consistently to a specific stimulus, such as
vibrations of the throat and/or barking noise. The correction should startle the dog sufficiently to
interrupt the unwanted behavior and deter repetition of that behavior (Coleman and Murray, 2000).
The element of surprise of a disruptive stimulus may be responsible for deterring barking (Beaudet,
2001). Alternatively,dogs with citronella spray collars may be distractedby the odor and try to locate
the source, or calmed by the odor, startled by the noise, or find the spray’s odor offensive (Juarbe-
Diaz, 1997). But regardless of which collar is used, experts have stressed that no device should be
recommended without concomitant behavior modification (Juarbe-Diaz and Houpt, 1996).
The purposes of this study were to (1) measure plasma cortisol and ACTH levels as indicators
of physiological stress in healthy adult dogs wearing electronic and lemon spray bark control
collars; (2) determine the effectiveness of the two collar types for control of barking.
2. Materials
2.1. Outline of study
On wk 1, 24 mixed breed kennel dogs were screened (physical examination, complete blood count,
serum biochemistry, and plasma cortisol measurement) to ensure that they were healthy. Dogs also were
J.E. Steiss et al. / Applied Animal Behaviour Science 106 (2007) 96–106 97
tested to ensure they barked at an unfamiliar dog. Dogs admitted to the study were randomly assigned to
three groups: control, electronic bark collar or lemon spray bark collar (n= 8 per group). On wk 0
(acclimation baseline), dogs wore inactivated collars for 30 min/day for 3 consecutive days. On wks 1 and 2,
dogs wore an activated collar for 30 min/day for 3 consecutive days. Controls wore an inactivated collar. The
bark stimulus was an unfamiliar dog walked in front of the run at specific time periods.
2.2. Subjects
The project was approved by the Animal Care and Use Committee and the Human Participant Review
Committee, Tuskegee University. The original population was comprised of 24 dogs housed in a private no-
kill shelter. All dogs had been relinquished by their owners. The study was approved by the shelter’s
manager and board of directors, who acknowledged that excessive barking was a major cause of
relinquishment of dogs and an impediment to adoption. It was hoped that participating in the study would
enhance the adoptability of the dogs. Three dogs were eliminated on wk 0 for failure to bark when presented
with the bark stimulus (an unfamiliar dog on leash) while wearing an inactivated collar. Because these three
dogs had barked at unfamiliar dogs during screening on wk 1, the investigators conjectured that the three
dogs may have experienced bark collars previously (Moffat et al., 2003). The 21 remaining dogs included 11
males (9 intact, 2 neutered), and 10 intact females. All dogs were considered healthy based on physical
examination, serum biochemistry, and complete blood count. Body weights ranged from 15.5 to 35.6 kg
(mean, 22.5 kg). Mean age was 20 months (S.D. 14 months; range 10–64 months). Most dogs were mixed
breed; 15 dogs appeared to be Labrador Retriever crosses. Mean duration of housing at the kennel prior to
the study was 5 months (S.D. 3 months; range 1–15 months).
The initial screening prior to acceptance into the trial included a cursory behavior evaluation performed
while observing each dog in its run (Schaffer and Schaffer, 1996). Dogs admitted to the trial were classified
as playful (n= 5), playful and attentive (n= 2), attentive (n= 3), submissive (n= 7), submissive and
attentive (n= 1), passive submissive (n= 1) and submissive and slightly fearful (n= 2).
2.3. Housing
Dogs were housed individually in an animal shelter, in an indoor kennel with concrete floors, side walls
with the lower half concrete and the upper half wire mesh, and wire mesh doors. Individual runs consisted of
two sections (each approximately 1.2 m 2.4 m) separated by a guillotine door. One section of each run
faced a concrete wall toward the interior of the building and was air conditioned. The section on the other
side of the guillotine door faced a concrete walkway and windows overlooking a yard, with fans but no air
conditioning. Dogs were moved to this part of the run for recording sessions. Two dogs were studied at the
same time, with approximately 10 empty runs and a hallway between each pair of dogs (total distance
approximately 14 m). With this arrangement, the dogs were not in direct view of each other. Only personnel
involved in the study were admitted to the area during testing in order to minimize distractions. All dogs had
been housed in their run for a minimum of 7 days to avoid stress associated with exposure to a new
environment.
Dogs were kept on the same commercial dog food and feeding schedule over the entire study. Recordings
were performed between 11:00 and 16:00 h. Dogs were fed once per day at 16:45 h. Ambient temperature
and humidity were measured at the start and end of each session. Ambient temperature ranged from 23 to
33 8C. Humidity ranged from 57 to 97%.
2.4. Study schedule and data acquisition
Wk 1 (screening). Dogs were screened by physical examination, blood collection for complete blood
count, serum biochemistry, and plasma cortisol measurement, and presentation of the bark stimulus (an
unfamiliar dog on leash) to ensure that they barked. Then, dogs were randomly assigned to one of three
groups (control, electronic bark collar or lemon spray bark collar, n= 8 per group), by picking a card out of a
hat.
J.E. Steiss et al. / Applied Animal Behaviour Science 106 (2007) 96–10698
Wk 0 (acclimation baseline). Dogs wore inactivated collars 30 min/day for 3 consecutive days. Data were
recorded on wk 0 d 3.
Wks 1 and 2. Dogs wore an activated collar 30 min/day for 3 consecutive days. Controls wore an
inactivated collar. Data were recorded on 3 consecutive days for both weeks.
Plasma cortisol was measured five times (wk 1, wk 0 d 3, wk 1 d 1, wk 1 d 3 and wk 2 d 3). ACTH was
measured wk 0 d 3 and wk 1 d 1. Barking duration and activity were measured each session.
Two observers evaluated two dogs simultaneously in individual runs spaced 10 empty runs apart (14 m).
Dogs were paired based on the location of their kennel. Approximately equal distances were maintained
between all pairs of test dogs. A third person presented the bark stimulus. The observer sat quietly,
approximately 1.2 m in front of the run, in full view of the test dog. A digital camcorder mounted on a tripod
was positioned a fixed distance behind the observer to videotape each session. The observer timed barking
with a stopwatch, and recorded the number of collar corrections. Each observer held a pocket voice recorder
and clipboard to record observations. At the end of each 30 min session, personnel entered the run, turned off
activated collars, and took blood samples on designated days.
2.5. Bark stimulus
The bark stimulus was an unfamiliar dog walked on leash in front of the run of the test dog. A different
dog was presented at each of the three presentations during the 30 min session (at 5, 15 and 25 min), for 30 s
per presentation. The unfamiliar dogs were selected to be dogs which themselves did not bark during testing.
These dogs were housed in another part of the kennel.
2.6. Test collars
Test collars were a lemon spray bark control collar (Model SBC100 Spray bark control collar containing
lemon spray [Lemon Spray RFA-164, Petsafe Corp., Knoxville TN]) and an electronic bark control collar
(Deluxe Bark Collar Model DBC100 electrical stimulation collar; Radio Systems Corp., Knoxville, TN).
The spray collar emitted a lemon-scented spray but did not contain citronella. Vibration detection triggered
the spray. The electronic collar used a combination of vibration and sound detection techniques such that the
device activated when both the sound and vibration of a bark were detected simultaneously. The
approximate time from detection of the bark to correction is 152 ms for the electronic collar, and
67 ms for the spray collar.
Activated electronic collars were set at the ‘‘off’’ position for wk 0 acclimation, and ‘‘low’’ intensity
setting on wks 1 and 2. The electronic collar was positioned high on the neck, immediately below the jaw.
The lemon spray collar was positioned 2–4 cm lower, so that the lower jaw did not block the spray outlet of
the canister. Collars were checked each week to ensure proper functioning. During most of the study, each
dog wore its own test collar.
Half the controls wore an electronic collar that was turned off, and the other half wore a lemon spray
collar that had previously been filled with spray but was empty and turned off.
2.7. Barking and activity measurements
The observers measured barking duration with a stop watch for the entire 30 min, at each recording
session. Barking data were verified by review of the videotapes at a later time. Measurements included
whining as well as barking.
An activity indicator was obtained by counting the number of times the left front foot of the dog crossed
one of the grid lines painted on the floor. The left front foot was chosen arbitrarily for ease of counting, and
as a consistent standard of measure. Grid lines, approximately 2.5 cm wide, had been painted on the floor of
each run. Grid lines were oriented from left–right and front–back, resulting in 0.6 m 0.6 m squares. The
criterion for crossing a line was that the entire foot print crossed the line. The activity data were determined
by the evaluators by reviewing the videotapes at a later time.
J.E. Steiss et al. / Applied Animal Behaviour Science 106 (2007) 96–106 99
2.8. Cortisol and ACTH measurements
Blood samples were taken within 4 min of opening the door to the run at the end of the 30 min recording
sessions. Blood was drawn from the cephalic vein into a 6 ml syringe. Each dog was returned through the
guillotine door to the other side of its run immediately after blood sampling. The blood was divided into two
EDTA vacutainer tubes (3 ml volume) and stored on ice for transport. Several hours later, the tubes were
centrifuged (4000 rpm 10 min) and aliquots of plasma were frozen at 28 8C. Previous studies indicated
that samples could be kept on ice for at least 6 h with no change in cortisol (Steiss, unpublished data). The
frozen samples were assayed within 4 days.
The exception to the protocol of drawing blood within 4 min of approaching the dog was during the
initial screening (wk 1), when some dogs were walked on leash from their run to the treatment room and
were subjected to the stress of manual restraint for physical examination before drawing blood. Therefore,
wk 0 values are considered more accurate indicators of baseline than wk 1.
Assays were performed by the Endocrinology Laboratory, College of Veterinary Medicine, Auburn
University. Cortisol and ACTH concentrations were assayed in duplicate using commercial radio-immu-
noassay kits (Coat-A Count Cortisol, Diagnostic Products Corp., Los Angeles, CA; ACTH, Nichols Institute
Diagnostics, San Clemente, CA). The methodology for the cortisol assay (Kemppainen et al., 1983) and
ACTH assay (Gould et al., 2001) have been reported previously. The cortisol assay sensitivity is 5 nmol/l.
The only steroids which have been shown to have significant (>3%) cross reaction are prednisolone and 11-
deoxy-17-hydrocorticosterone (Kemppainen et al., 1983). The limit of detection of the ACTH assay is 1 pg/
ml (Gould et al., 2001). The manufacturer states that related peptides such as alpha MSH and beta endorphin
show no cross reaction.
2.9. Statistics
The experiment was evaluated as a repeated measures over time for the two treatments (electronic and
lemon spray collars) and the control group. Data were analyzed by the general linear model (GLM)
procedure of SAS (SAS Institute, 1990) with treatments and time as the main effects. Barking, plasma
cortisol, ACTH and activity were measured repeatedly over time. Significantly different main effects
(treatments and time) for various response measurements were further classified using the all pairs Tukey–
Kramer honestly significant difference (HSD) test (Tukey, 1953). Within the main effect of time, the data
were also analyzed for treatment effect by the GLM procedure of SAS (SAS Institute, 1990) and Scheffe’s
test for multiple comparisons.
3. Results
3.1. Barking
Starting the 2nd day wearing either an activated electronic or lemon spray collar (wk 1 d 2),
barking time was reduced to a mean of 1.8 s or less during the 30 min recording period, P<0.05.
The values on wk 1 d 3 were not significantly different compared to controls probably due to the
large standard deviation in the control group on that day. There was no significant difference
between collar types. We did not notice any barking that could be attributed to interaction
between the dogs (Table 1).
3.2. Number of collar corrections
The mean number of corrections during the 30 min recording sessions decreased to 0.0 for
both collar types on the 3rd day wearing an activated collar (wk 1 d 3) (Table 2).
J.E. Steiss et al. / Applied Animal Behaviour Science 106 (2007) 96–106100
J.E. Steiss et al. / Applied Animal Behaviour Science 106 (2007) 96–106 101
Table 1
Summary of barking (measured in s, mean S.E.M.)
Group
a
Wk 0 d 3
b
(D)
acclimation to
inactivated collar
Wk1d1(EJ)
1st day wearing
active collar
Wk 1 d 2 (FJ)
2nd day wearing
active collar
Wk1 d 3 (GJ)
3rd day wearing
active collar
Wk 2 d 1 (HJ)
4th day wearing
active collar
Wk 2 d 2 (IJ)
5th day wearing
active collar
Wk 2 d 3 (J)
6th day wearing
active collar
Control
collar (A)
(n=7)
48.1 11.0 (100%)
c
32.7 9.8 (69%) 26.0 7.9 (54%) 40.9 23.3 (85%) 55.4 18.4 (115%) 38.4 16.1 (79%) 71.6 27.4 (150%)
Electronic
collar (BC)
(n=6)
102.4 18.1 (100%) 16.0 5.6 (16%) 1.8
d
1.3 (2%) 1.0 1.0 (1%) 1.3
d
1.0 (1%) 0.7 0.7 (1%) 0.7
d
0.7 (0%)
Lemon spray
collar (C)
(n=8)
65.4 20.4 (100%) 12.8 4.3 (20%) 0.9
d
0.4 (1%) 0.2 0.2 (0%) 0.0
d
0.0 (0%) 0.0
d
0.0 (0%) 0.4
d
0.2 (0%)
Barking was measured over 30 min. The bark stimulus was a strange dog walked in front of the run for 30 s on three separate occasions during the 30 min test period. Overall
comparisons within columns are designated by letters A–C. Treatment groups bearing the same letter are not significantly different, P>0.05. Overall comparisons within rows are
designated by letters D–J. Times bearing the same letter are not significantly different, P>0.05.
a
Treatments were significantly different, P<0.05 (d.f. = 2; F= 16.71).
b
Time was significantly different, P<0.05 (d.f. = 6; F= 8.28).
c
The percentage in parentheses represents the mean on that day divided by the mean of the acclimation period (wk 0 d 3).
d
Interaction between treatment and time was significantly different, P<0.05 (d.f. = 12; F= 2.81). Significantly different from control at this time point, P<0.05.
3.3. Activity
There was no significant difference between the lemon spray and electronic collar groups or
electronic and control groups. The lemon spray group was significantly less active than the
control group throughout the study, P<0.05. The time periods were not significantly different,
P>0.05 (Table 3).
3.4. Cortisol
During the initial screening prior to admission to the study, the mean cortisol level for all 21
dogs was 83.6 nmol/l (S.E.M., 13.4 nmol/l). Mean plasma cortisol values remained within the
reference range for all groups throughout the study. On the 1st day wearing an activated bark
collar, mean plasma cortisol increased to 169% of acclimation baseline levels for both collar
types, but this was not statistically significant (P>0.05). There was no significant difference
between the control, electronic collar and lemon spray collar groups, P>0.05. There was a
significant overall time effect (P<0.05) (Table 4).
J.E. Steiss et al. / Applied Animal Behaviour Science 106 (2007) 96–106102
Table 2
Summary of number of corrections per dog from bark control collars during the first 3 days of wearing activated collars
(mean S.E.M.)
Group Wk 1 d 1 1st day
wearing active collar
Wk 1 d 2 2nd day
wearing active collar
Wk 1 d 3 3rd day
wearing active collar
Control collar (n= 7) Not applicable Not applicable Not applicable
Electronic collar (n= 6) 4.0 0.55 0.0 0.05 0.0 0.05
Lemon spray collar (n= 8) 2.0 0.53 1.0 0.21 0.0 0.04
Observations were made over 30 min.
Table 3
Summary of activity (crossing grid lines on floor, mean S.E.M.) for dogs in bark collar study
Group
a
Wk 0 d 3 acclimation
to inactivated collar
Wk 1 d 1 1st day
wearing active collar
Wk 1 d 3 3rd day
wearing active collar
Wk 2 d 3 6th day
wearing active collar
Control
collar (AB)
(n=7)
399.7 193.1 (100%)
b
378.9 108.4 (95%) 374.0 110.0 (94%) 337.3 119.8 (84%)
Electronic
collar (BC)
(n=6)
283.3 58.2 (100%) 217.0 54.4 (77%) 236.7 68.6 (84%) 285.5 95.8 (101%)
Lemon spray
collar (C)
(n=8)
262.2 86.5 (100%) 193.6 49.9 (74%) 166.1 48.7 (63%) 155.5 29.3 (60%)
Activity was measured over 30 min. Measurements were calculated by an observer counting the number of times the dog’s
left front foot crossed over a grid line during the 30 min test period. Grid lines (2 cm wide) were painted on the floor of
each run resulting in a 2 ft. 2 ft. square pattern. Overall comparisons within columns are designated by letters A–C.
Treatments groups bearing the same letter are not significantly different, P>0.05.
a
Treatments were significantly different, P<0.05 (d.f. = 2; F= 3.84). Time, and treatment time interactions were
not significant, P>0.05.
b
The percentage inparentheses represents the mean on that day divided by the mean of the acclimation period (wk 0 d 3).
3.5. ACTH
Groups showed no significant difference in plasma ACTH levels, P>0.05. The plasma
ACTH values (pg/ml, mean S.E.M.) for the control group were 14.3 1.8 (wk 0 d 3) and
15.0 1.7 (wk 1 d 1). The corresponding values for the electronic collar group were 20.2 5.6
(wk 0 d 3) and 28.2 9.8 (wk 1 d 1); values for the lemon spray collar group were 13.5 1.3 (wk
0 d 3) and 16.7 1.7 (wk 1 d 1). The reference range for resting ACTH (Endocrine Diagnostic
Service Laboratory, Auburn University) is 10–80 pg/ml.
4. Discussion
In this study, barking was significantly decreased starting the 2nd day of wearing either an
electronic or lemon spray collar, with no significant difference between the collar types.
Evaluations of bark control collars have been reported previously. Investigators in Australia
randomly surveyed people who had used a collar mounted electronic training device (Coleman
and Murray, 2000). They reported that 97% of respondents were satisfied with the product, and
30% considered their dogs to be calmer after using the electronic collar. Juarbe-Diaz and Houpt
(1996) conducted an in-home study comparing citronella spray collars and electronic shock
collars for efficacy and user satisfaction after a 2 week trial. They found that citronella spray
collars decreased barking 89% whereas electronic collars decreased barking 44%. There was no
explanation for this difference between collar types. Most owners in that study expressed a
preference for the citronella spray collar and perceived it as more humane. Moffat et al. (2003)
used citronella collars on dogs in a veterinary hospital and a kennel; out of 62 dogs, barking
ceased in 40 and decreased in 17 dogs with the collar. In a colony of Beagles, citronella collars
reduced barking noise from a mean of 106 to 70 dB (Moffat et al., 2003). The results of our study
cannot be compared to a more recent report on electronic (‘‘shock’’) collars because that study
examined electronic collars during guard dog training, not as bark deterrents (Schilder and van
der Borg, 2004).
Elevation in blood cortisol concentration has long been used as an indicator of stress in
mammals (Beerda et al., 1998). Rushen (1991) has cautioned about attempts to make claims
concerning animal welfare based on physiological data, given the complexity of the pituitary–
adrenocortical axis. Corticosterone levels have been reported to fluctuate systematically in
J.E. Steiss et al. / Applied Animal Behaviour Science 106 (2007) 96–106 103
Table 4
Summary of canine plasma cortisol concentrations (nmol/l) in bark collar study (mean S.E.M.)
Group Wk 0 d 3
a
(AB)
acclimation to
inactivated collar
Wk 1 d 1 (A)
1st day wearing
activated collar
Wk 1 d 3 (B)
3rd day wearing
activated collar
Wk 2 d 3 (B)
6th day wearing
activated collar
Control collar (n= 7) 33.4 5.0 (100%)
b
31.6 7.4 (97%) 22.0 2.3 (67%) 27.3 4.5 (82%)
Electronic collar (n= 6) 61.3 19.1 (100%) 103.3 31.8 (169%) 35.0 7.1 (57%) 39.3 9.1 (64%)
Lemon spray collar (n= 8) 36.0 4.7 (100%) 61.1 14.9 (169%) 37.2 9.0 (103%) 33.9 5.0 (94%)
Reference range for canine baseline cortisol, Endocrine Diagnostic Service Laboratory, Auburn University: 10–160 nmol/
l. Mean plasma cortisol concentration for all 21 dogs at screening prior to admission to the study was 83.6 nmol/l (S.E.M.,
13.4 nmol/l). Overall comparisons within rows are designated by letters A and B. Times bearing the same letter are not
significantly different, P>0.05.
a
Time was significantly different, P<0.05 (d.f. = 3; F= 7.36). Treatments, and treatment time interactions were not
significant, P>0.05.
b
The percentage inparentheses represents the mean on that day divided by the mean of the acclimation period (wk 0 d 3).
response to changes in emotional state (Hennessy et al., 1979). In the present study, on the 1st day
of wearing an activated bark collar, mean plasma cortisol increased to 169% of acclimation
baseline levels for both collar types, but this was not statistically significant (P>0.05).
Throughout this study, the average cortisol level in dogs wearing either bark collar remained
within normal range. In a study which examined dogs in an animal shelter, Hennessy et al. (2002)
reported plasma cortisol concentrations ranging from approximately 10 to 20 ng/ml (equivalent
to 27.5–55 nmol/L), comparable to the values in this study.
Concern has been expressed that the stress of blood sampling limits the usefulness of cortisol
measurement (Wielebnowski, 2003). However, there is an interval after a stressful stimulus
before cortisol rises. Hennessy et al. (1979) documented increases in corticosterone and ACTH in
rats after 10 min, but not 2.5 min, of exposure to a stressful stimulus. In later studies, Hennessy
collected samples from dogs within 4 min after removing the dog from its cage or the test area
(Hennessy et al., 1997, 1998, 2002). In this study, in order to avoid a rise in plasma cortisol which
could be associated with the stress of restraint and venipuncture, blood samples on wks 0–2 were
collected within 4 min of the operator opening the door to the dog’s run.
Mean plasma cortisol levels in this study were higher on wk 1 (initial physical examination)
than wk 0 (acclimation). On wk 1, some dogs were moved from their run to a treatment room
and were restrained for physical examination before drawing blood. This change in handling the
dogs was not due to any difference in the dogs. Transfer to a different room and/or handling and
restraint of the dogs likely account for the higher mean cortisol levels. Therefore, wk 0 values
were considered more accurate indicators of resting baseline than wk 1. Hennessy et al. (1998)
found that handling a dog and taking a venous blood sample raised plasma cortisol. Some
investigators have expressed concern that dogs housed long term in shelters or laboratories are
unable to increase their cortisol levels due to chronic stress (Hennessy et al., 2002). The findings
on wk 1 show that the dogs were able to elevate their blood cortisol.
Several factors in the experimental design were controlled in order to avoid extraneous causes
of elevated plasma cortisol concentrations. Dogs have been shown to have higher plasma cortisol
concentrations during their first 3 days of confinement in an animal shelter compared to dogs
housed in the shelter for longer periods (Hennessy et al., 1997). In our study, dogs were housed a
minimum of 7 days in the kennel in which the study was conducted. Also, 10 empty runs
separated each pair of dogs, thereby avoiding the possibility of dogs in adjacent runs being
exposed to lemon spray, or being influenced by the behavior of the dog in a neighboring run. To
minimize diurnal variations in cortisol, dogs were studied within a time frame of 11:00–16:00 h.
Blood sampling was scheduled more than 2 days apart to allow for recovery of the adrenal axis
between sampling. The dogs were screened by age (approximately 1–4 years of age), breed and
behavior. Breeds that might be considered to have a higher threshold for pain, such as Pit Bulls
and Jack Russell terriers, were not studied. Dogs that demonstrated aggressive tendencies on the
behavioral screening were not used.
Measurements of plasma cortisol and behavior may be preferable to measurement of either
one alone. Our study reports one behavioral measure of activity, namely, the number of times
dogs moved across sectors (grid lines) marked on the floor of each run (Beerda et al., 1998). The
citronella group was less active than the other groups at all time points in this study. That result is
likely due to the small number of animals and individual variation.
Some studies have reported barking as ‘‘episodes per minute’’ (Moffat et al., 2003). However,
distinguishing a single bark from episodes of multiple short barks can be difficult and could yield
unacceptable inter-rater reliability. Therefore, in this study, vocalization time, measured with a
stop watch, has been reported instead.
J.E. Steiss et al. / Applied Animal Behaviour Science 106 (2007) 96–106104
Some studies indicate that dogs may habituate to the citronella spray collar (Moffat et al.,
2003; Wells, 2001) although habituation has not always been found (Beaudet, 2001). No
evidence of habituation was seen in this study with dogs wearing bark collars intermittently over
a 2 week period. Juarbe-Diaz and Houpt (1996) commented that dogs quickly learned not to bark
when they wore citronella spray collars and to bark when the collar was not worn. The possibility
of habituation to the collars over a longer time period than the present study would be a relevant
issue to investigate in future studies.
5. Conclusions
Dogs wore a lemon spray bark collar, electronic bark collar or an inactivated bark collar (n=8
per group) for 30 min/day, 3 days per week for 2 weeks, after an acclimation period the previous
week. Both electronic and lemon spray bark collars significantly reduced barking, with no
significant difference between the two types of collars. The amount of barking was significantly
reduced starting the 2nd day that the dogs wore a bark collar. The mean number of corrections
decreased to 0 by the 3rd day for both collar types. Mean plasma cortisol levels were within the
reference range for all groups throughout the study. Plasma cortisol, as well as ACTH levels, did
not differ among groups (P>0.05). Activity did not change significantly over time (P>0.05).
The findings of this study may contribute additional information in the animal welfare debate
regarding whether the use of bark control collars is humane. In the present study, with dogs
wearing bark control collars intermittently over a 2 week period, the collars effectively deterred
barking without statistically significant elevations in plasma cortisol, compared to controls, at
any of the time points measured.
Acknowledgements
This study was funded by Radio Systems Corporation (10427 Electric Ave, Knoxville, TN
37932) and the Department of Health and Human Services’ Health and Services Administration,
Bureau of Health Professions under Tuskegee University’s Center of Excellence Grant.
Veterinary students, S. Chandler, J. Johnson, J. Persaud and P. Reisdorff, Tuskegee University
School of Veterinary Medicine, are acknowledged for their contributions. Dr. R. Kemppainen
(Endocrinology Laboratory, College of Veterinary Medicine, Auburn University) provided
cortisol and ACTH assays. The authors thank Dr. James Wright, Auburn University, for helpful
discussion on statistical analyses.
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