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Characteristics of compulsive tail chasing and associated risk factors in Bull Terriers

Authors:
  • Animal Behavior Consultations, LLC

Abstract

To evaluate and define the characteristics of tail chasing in Bull Terriers and explore the association between tail chasing and other behavioral and physical characteristics. Survey and case-control study. 333 Bull Terriers (145 dogs with tail-chasing behavior and 188 unaffected dogs). Owners of Bull Terriers with tail-chasing behavior were surveyed regarding the age of onset, triggers, frequency, duration, interruptability, degree of disruption to the dogs' normal functioning and the owners' relationship with the dog, and associated medical and physical consequences. Associations of tail chasing with various behavioral and physical characteristics were examined by comparison of dogs with tail-chasing behavior with unaffected dogs. Phenotypic and developmental descriptions of tail chasing in Bull Terriers were defined. Associations of tail chasing with sex, trance-like behavior, and episodic aggression were found. Males were at an 8% greater risk for the diagnosis of tail chasing than females. Phobias and owner-directed aggression did not significantly associate with tail chasing in the final log-linear model, but did have significant associations in earlier analyses that did not include the behaviors of episodic aggression and trance-like behavior. In Bull Terriers with tail-chasing behavior, there was a slight increase in the susceptibility of males to develop tail-chasing behavior, compared with females. A close association of tail chasing with trance-like behavior and episodic aggression was identified.
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Tail chasing is a repetitive behavior that is expressed
as slow to rapid circling with the dog’s attention di-
rected toward the tail or rapid spinning in tight circles
with no apparent focus on the tail. Within the same
dog, these 2 forms of expression (slow, focused; rapid,
unfocused) may be expressed interchangeably. Slow
chasing focused on the tail often precedes rapid unfo-
cused spinning bouts. In its most advanced stage, tail
chasing is a debilitating and potentially life-threatening
behavioral condition.
Classic tail chasing, which is frequently bidirec-
tional, is not caused by organic problems such as a brain
tumor, local irritation, or other medical conditions, and
neither is it typically an attention-seeking behavior.
Many dogs chase their tail when separated from their
owners, and when fully engaged in the behavior, the
dogs appear dissociated from their environment and re-
sistant to any form of interruption. They are often unre-
sponsive to their owner’s commands when in this state,
many shun their owner’s attention, and some become
aggressive when attempts to interrupt them are made.
Bull Terriers that are punished for tail chasing will often
remove themselves to a location remote from the owner
to engage in the behavior. Although tail chasing occurs
Characteristics of compulsive tail chasing
and associated risk factors in Bull Terriers
Alice A. Moon-Fanelli, phd; Nicholas H. Dodman, bvms; Thomas R. Famula, phd; Nicole Cottam, ms
Objective—To evaluate and define the characteristics of tail chasing in Bull Terriers and ex-
plore the association between tail chasing and other behavioral and physical characteristics.
Design—Survey and case-control study.
Animals—333 Bull Terriers (145 dogs with tail-chasing behavior and 188 unaffected dogs).
Procedures—Owners of Bull Terriers with tail-chasing behavior were surveyed regarding
the age of onset, triggers, frequency, duration, interruptability, degree of disruption to the
dogs’ normal functioning and the owners’ relationship with the dog, and associated medical
and physical consequences. Associations of tail chasing with various behavioral and physi-
cal characteristics were examined by comparison of dogs with tail-chasing behavior with
unaffected dogs.
Results—Phenotypic and developmental descriptions of tail chasing in Bull Terriers were
defined. Associations of tail chasing with sex, trance-like behavior, and episodic aggression
were found. Males were at an 8% greater risk for the diagnosis of tail chasing than females.
Phobias and owner-directed aggression did not significantly associate with tail chasing in
the final log-linear model, but did have significant associations in earlier analyses that did
not include the behaviors of episodic aggression and trance-like behavior.
Conclusions and Clinical Relevance—In Bull Terriers with tail-chasing behavior, there was
a slight increase in the susceptibility of males to develop tail-chasing behavior, compared
with females. A close association of tail chasing with trance-like behavior and episodic ag-
gression was identified. (J Am Vet Med Assoc 2011;238:883–889)
in a variety of breeds, it is most commonly observed in
Bull Terriers and German Shepherd Dogs.1,2
The disorder has previously been attributed to
opioid-mediated stereotypy3 or a seizure-related neu-
rologic syndrome phenomenon.4,5 The seizure-related
neurologic syndrome hypothesis suggests a putative
association between tail chasing and episodic aggres-
sion, trance-like behavior, hyperactivity, sound sensi-
tivity, and fear responses and phobias. It has also been
hypothesized that this neurologic syndrome has some
features in common with another disease in Bull Terri-
ers, lethal acrodermatitis.6 In addition to having derma-
tologic problems, dogs with lethal acrodermatitis may
have hydrocephalus and characteristic behavioral signs,
such as aggression and prolonged staring. Recent stud-
ies2,7–9 investigating the clinical signs, development,
and response to pharmacological treatment of tail chas-
ing in dogs support a compulsive etiology similar to hu-
man obsessive-compulsive disorder. The purpose of the
study reported here was to define and evaluate charac-
teristics of tail chasing in Bull Terriers and any associa-
tion with other physical and behavioral characteristics
as a preliminary step toward future investigation of the
inheritance of tail chasing in Bull Terriers.
Materials and Methods
Study participants—Dog owners for the study
were solicited through clients of Tufts University Cum-
mings School of Veterinary Medicine, the Bull Terrier
Club of America, Bull Terrier Welfare Foundation, lo-
cal dog shows, Silverwood National Bull Terrier Spe-
From the Department of Clinical Science, Cummings School of Veter-
inary Medicine, Tufts University, North Grafton, MA 01536 (Moon-
Fanelli, Dodman, Cottam); and the Department of Animal Science,
School of Veterinary Medicine, University of California-Davis, Da-
vis, CA 95616 (Famula). Dr. Moon-Fanelli’s present address is Ani-
mal Behavior Consultations LLC, Brooklyn Veterinary Hospital, PO
Box 285, Brooklyn, CT 06234.
884 Scientific Reports JAVMA, Vol 238, No. 7, April 1, 2011
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cialty show, and the Bull Terrier Neurological Disorder
website. Convenience sampling methods were used
to increase the number of dogs included in the study.
Dogs were assigned to either the affected or unaffected
group on the basis of the presence or absence of tail
chasing as described by owners. All dogs included in
the study were examined by the owner’s local veterinar-
ian or evaluated at Tufts University Cummings School
of Veterinary Medicine. Most owners of Bull Terriers
with tail-chasing behavior had contacted a veterinarian
for treatment advice prior to participating in the study.
Owners of dogs with daily tail-chasing behavior typical-
ly requested medication to treat the condition because
of the severity and disruptive nature of the behavior. No
medical conditions associated with the onset or propa-
gation of tail chasing were reported. Owners completed
a research questionnaire that was designed to identify
those dogs affected with compulsive tail chasing as op-
posed to other conditions.
Survey—Owners of dogs with tail-chasing behav-
ior were sent a survey designed to solicit information
regarding the appearance of tail chasing, age of onset,
frequency of bouts, duration of bouts, and eliciting trig-
gers. Owners were asked to provide their best estimate
for age of onset and frequency and duration of tail chas-
ing bouts on the basis of their history of living with the
dog in the home. Questions regarding various physical
and behavioral conditions were also included in the sur-
vey. As new behavior patterns emerged over the 16-year
duration of data gathering, 2 additional questions were
added to assess the degree of interference that the dog’s
tail chasing caused regarding the dog’s quality of life and
the owner’s relationship with the dog. Subsequent study
participants were asked to report how the amount of
time the dog spent tail chasing interfered with its nor-
mal daily activities and relationship with the owner. The
owner was asked to score 0 for no interference, 1 for
slight interference, 2 for mild to moderate interference,
3 for definite interference that was still manageable, and
4 for interference that incapacitated every aspect of the
dog’s or owner’s life. When responses were unclear, own-
ers were contacted directly for clarification.
For comparative purposes, sex and neuter status
as well as behavioral data were collected for all Bull
Terriers in the study regardless of whether they had
tail-chasing behavior. Owner-directed aggression was
assessed by having owners complete a previously pub-
lished checklist indicating interactions in which their
dog might challenge them, including but not limited
to resource guarding, routine handling, and mild re-
straint.10 Owner-directed aggression included behaviors
of growling, lift lip, snapping, or biting. Episodic ag-
gression was defined as recurrent, unprovoked attacks
directed toward people, other animals, or objects in the
household. The attacks are explosive, violent, sudden,
and unpredictable, with little to no provocation and no
typical warning signals. The behavior is out of character
for the dog’s normal demeanor. An awake but peaceful
dog may have a transition state, often of quite short du-
ration, in which the eyes glaze, followed by an attack.
Statistical analysis—The survey was designed to
evaluate dogs on a large set of binary random variables,
among these being tail-chasing behavior (yes or no), sex
(male or female), coat color (white or other color), and
a list of other behavioral variables. Data were analyzed
in accordance with the concept of log-linear models.11
By use of this approach, tail chasing was considered as
just another observed binary random variable (ie, tail
chasing was not considered as caused by the action of
other variables). The count of dogs was evaluated in
cross-sectional tables to evaluate whether tail-chasing
behavior is observed independent of other behaviors,
sex, or coat colors. The modeled variable was thus a
count, not the presence or absence of tail chasing; the
count of dogs was classified by sex, coat color, tail chas-
ing status, and all other binary behavior observations.
The first step in this analysis was to estimate the
correlation between all the assembled elements of the
survey. Being binary characters, the polychoric correla-
tion12 was computed by use of a software program of
the public domain.a Once computed, these correlations
were used to ascertain those behaviors and characters
that were most closely correlated with tail chasing.
Nine such characters were found to have estimates of
correlations with tail chasing, and with each other, to
warrant further investigation. However, 7 behavioral
variables (fly-snapping, shadow and light chasing, fly-
snapping and shadow chasing combined, flank suck-
ing, owner aggression 1 interaction, owner aggression
2 interaction, and deafness) were found to have poorly
estimated correlation coefficients (ie, SEs well above
1.0) and were excluded from further analysis.
The remaining 10 variables formed the basis of a
series of log-linear analyses. All possible sets of 8 vari-
ables, where tail chasing was kept in each set (this be-
ing the variable of principle interest), were evaluated.
This was done to balance the interest in estimating un-
known effects against the preponderance of empty cells
given the limited number of dogs observed across the
many subclasses. The initial analyses fit all 8 variables,
including models for 2- and 3-way interactions. In each
setting, nonsignificant variables were removed and a
suitable submodel was chosen through comparisons
of the Akaike Information Criterion and the residual
deviance. In repeating this process over the 9 subsets
of variables, a subset of variables and their interactions
were arrived at, which were consistently found to be
associated with each other. All computations were per-
formed with the general linear model function of the
R programing language with the dependent variable of
counts and a Poisson model with and without consid-
eration of overdispersion.a
Results
Data were collected on 333 Bull Terriers, 145 dogs
with tail-chasing behavior, and 188 unaffected dogs;
however, not all dogs had information recorded for
each descriptive trait. Because some owners did not
answer certain questions, the total number of dogs for
every variable varied.
Sex and neuter status—A total of 169 female and
164 male Bull Terriers were included in the analysis.
Reproductive status was not reported for 6 dogs; re-
productive status was known for 144 dogs with tail-
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chasing behavior and 183 unaffected dogs. Thirty-one
percent (45/144) of dogs with tail-chasing behavior
were neutered males, and 18% (33/183) of unaffected
dogs were neutered males. Thirteen percent (19/144) of
dogs with tail-chasing behavior were sexually intact fe-
males, and 23% (42/183) of unaffected dogs were sexu-
ally intact females. Thirty-one percent (44/144) of dogs
with tail-chasing behavior were spayed females, and
34% (62/183) of unaffected dogs were spayed females.
Twenty-five percent (36/144) of dogs with tail-chasing
behavior were sexually intact males, and 25% (46/183)
of unaffected dogs were sexually intact males.
Age of onset—Age of onset for tail chasing was
known or confidently estimated for 61% (89/145) of
dogs with tail-chasing behavior. The median age of
onset was 6 months. The range of age of onset was 2
months to 6 years of age.
Frequency and duration of bouts—Frequency
(daily tail chasing or less than daily tail chasing) was
recorded for 109 of the 145 dogs with tail-chasing be-
havior. Of these 109 dogs, 74% (81/109) chased their
tail daily while 26% (28/109) chased their tail less than
daily. Information on the duration (< 2 minutes, 2 to 30
minutes, > 30 minutes) of tail chasing was available for
67% (97/145) of the dogs with tail-chasing behavior.
The average duration of a tail-chasing bout was > 30
minutes for 28% (27/97) of the dogs. Average tail-chas-
ing bouts ranged from 2 to 30 minutes for 29% (28/97)
of the dogs. Average tail chasing bouts that lasted < 2
minutes were reported for 43% (42/97) of the dogs. For
94 dogs with tail-chasing behavior, both frequency and
duration data were available for cross tabulation. Of the
74 dogs that chased their tails daily for which duration
data were also available, 70% (52/74) did so for 2 to
30 minutes or > 30 minutes. By comparison, of the 20
dogs that did not chase their tails daily for which dura-
tion data were also available, only 10% (2/20) did so for
2 to 30 minutes or > 30 minutes (χ² = 23.8; P < 0.001).
Ability to interrupt—Owners of 99 dogs com-
pleted the question regarding the ease with which
they could interrupt their dog’s tail-chasing behavior.
Eighty-seven (88%) owners reported that they could
interrupt their dog from tail chasing. However, 48%
(42/87) of these owners reported that the dog would
immediately or within minutes resume tail chasing,
indicating that the interruption was only temporary.
Thirty-four percent (30/87) of owners indicated that
the dog would either not resume or resume tail chasing
at a later time, suggesting that these dogs were more
easily interrupted. Seventeen percent (15/87) of own-
ers reported that whether the dog resumed tail chasing
following an interruption depended on the situation.
If the dog was bored or stressed at the time, it would
likely resume immediately to within a few minutes. If
the dog’s attention could be redirected onto another ac-
tivity, the tail chasing could be successfully interrupted.
Ten percent (10/99) of owners could not interrupt their
dog’s tail chasing, and 2 owners (2%) did not attempt to
interrupt the behavior.
Triggers—As part of the survey, owners were
asked an open-ended question regarding what condi-
tions triggered the initial onset and continued elicita-
tion of their dog’s tail-chasing behavior. A total of 129
owners responded, but many owners listed > 1 trigger
for tail chasing, resulting in 239 reported triggers. Trig-
gers were grouped into 9 general categories. Thirty-one
percent (73/239) of triggers for tail chasing involved
situations that increased the dog’s level of arousal or
frustration. Examples included owner departures and
returns, visitors, food, presence of other dogs, aggres-
sive interactions with other dogs, exposure to moving
cars and bicycles, being released from a crate, going
outside, the owner cooking, or general excitement.
New, unpredictable or restrictive environments were
submitted as triggers for 18% (43/239) of dogs. This
category included crate confinement, new locations,
closed areas, room corners, and return to indoors. Lack
of mental or physical stimulation and insufficient inter-
action with the owner or conspecific was listed as a trig-
ger for 15% (35/239) of dogs. Sensitivity to sound was
also cited as a trigger for tail chasing for 10% (25/239)
of dogs. Specific sounds reported included loud noises,
rain on the roof and windows, running water, vacuum,
hair dryer, lawn mower, microwave bells, and other
household beeping-type alarms. Physical conditions as-
sociated with the onset and continued elicitation of tail
chasing were cited for 8% (20/239) of dogs and included
first or second estrus cycle, diarrhea, defecation, flatu-
lence, hunger, fatigue, allergies, and tail injury. Ten per-
cent (23/239) of owners reported no discernible trigger
associated with tail chasing and viewed the behavior as
spontaneous. Six percent (14/239) of owners reported
that their dog chased their tail at certain times of the
day or in response to other situations. A change in the
dog’s social group was associated with tail chasing in 2%
(4/239) of dogs. The sight of certain objects (eg, broom
or bag) triggered tail chasing in 1% (2/239) of dogs.
The development of tail-chasing behavior differed
among individuals, varying from a gradual to a sudden
onset. For some dogs, the onset of tail-chasing behavior
occurred suddenly with no apparent trigger, whereas
for other dogs, the onset coincided with exposure to
identifiable psychological, physiologic, or environmen-
tal triggers that were interpreted as increasing anxiety
or arousal levels.
Interference with dog’s quality of life and owner’s
relationship with dog—Fifty-one owners responded to
the question of how tail chasing interfered with their
dog’s normal activities. Twenty-seven percent (14/51)
of owners responded that the behavior occurred with
such high frequency and duration that it was nega-
tively affecting the dog’s ability to function to the point
of incapacitating every aspect of its life. Eighteen per-
cent (9/51) of owners reported definite interference but
that the behavior was still manageable. Sixteen percent
(8/51) reported that the interference was slight (5/51)
to mild to moderate (3/51). Thirty-nine percent (20/51)
reported that the dog’s tail-chasing behavior posed no
interference.
Fifty-two dog owners responded to the question
of how much the dog’s tail-chasing behavior interfered
with the relationship with their dog. Twenty-five percent
(13/52) of owners reported that their dog’s tail-chasing
behavior posed an incapacitating interference in the rela-
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tionship with their dog. Another 25% (13/52) of owners
reported that the tail-chasing behavior posed a definite
but manageable interference. Mild to moderate interfer-
ence was reported by 8% (4/52) of owners. Twelve percent
(6/52) of owners found that their dog’s tail-chasing behav-
ior caused a slight interference in the relationship with
their dog, whereas 31% (16/52) reported no interference.
Injuries—Dog owners were not specifically asked
to report injuries until later in the study. Fifteen dogs in-
curred tail injuries as a direct result of biting the tail dur-
ing tail-chasing bouts, 7 of which necessitated amputation
because of the severity of the injuries. Six dogs sustained
injuries to the head and tarsi in the form of abrasions and
cuts from banging into walls and furniture while tail chas-
ing. Two owners reported that their dog’s digital pads and
nails were severely worn because of excessive tail chasing.
Eight dogs that did not respond to treatment were euthan-
atized because of excessive tail chasing. Another 8 dogs
were euthanatized because of tail chasing in conjunction
with owner-directed aggression.
Degrees of expression—On the basis of clinical
impression data from owner reports regarding frequen-
cy, duration, interruptability, and degree of disruption
to the dogs’ normal functioning and the owners’ rela-
tionship with the dogs, 2 subsets of tail-chasing behav-
ior were identified that differed in degree of expression
for the Bull Terrier population of this study: clinical and
subclinical tail-chasing behavior.
Based on differences in frequency of expression only,
dogs with clinical tail-chasing behavior (81/109) were
those dogs that underwent multiple tail-chasing bouts
on a daily basis. They often appear dissociated from the
environment and unresponsive to owner commands.
These dogs were not easily interrupted from tail chasing,
and many had signs of anxiety or aggression if restrained.
If the owner was able to interrupt the dog from tail chas-
ing, usually by restraint or redirection onto a preferred
toy or object, the dog typically resumes immediately
upon release or removal of the object. On the basis of
owner reports, the duration of individual tail-chasing
bouts for dogs with clinical tail-chasing behavior gen-
erally ranged from 60 seconds to > 2 hours. Dogs with
clinical tail-chasing behavior often chased their tail daily,
usually to the exclusion of other normal activities, with
tail-chasing behavior occupying an owner-estimated
30% to 80% of the dog’s daily time budget. The behavior
was disruptive for both the dog and owner and in many
instances was viewed by the owner as incapacitating or
definitely interfering with the dog’s normal functioning
(23/51 [45%]) and relationship with the owner (26/52
[50%]). Owners reported that the dog often chased its
tail rather than interact with their human companions or
other dogs and commented that their dog was no longer
a good companion. These dogs were not reliably respon-
sive to training commands and could not be exercised,
as they chased their tail rather than walking on leash or
chasing a ball. A few dogs were reported to continue to
chase their tail while they urinated and defecated. Some
dogs with clinical tail-chasing behavior mutilated their
tail, sustained tail fractures while tail chasing, had weight
loss (either because they chased their tail rather than eat
or the excessive physical activity resulted in weight loss),
had signs of exhaustion, and had abraded foot pads, all
indicators of the severity of the behavior problem.
By definition, dogs with subclinical tail-chasing be-
havior (28/109) had an apparently milder form of tail
chasing that occurred typically 1 or 2 times/wk or 1 or
2 times/mo, usually in response to specific, predictable
stimuli. The episodes were comparatively short in dura-
tion, usually < 3 minutes, and were easily interrupted
by owners via distraction techniques. These dogs did
not appear dissociated from their environment, re-
sponded to owner commands while tail chasing, and
did not immediately resume tail chasing once they had
been interrupted. Their tail-chasing behavior was not
reported to interfere with the dog’s normal functioning
or its relationship with the owner. However, some dogs
with subclinical tail-chasing behavior later developed
clinical tail-chasing behavior in response to changes in
their environment or physiologic condition.
Fear responses and phobias—A total of 60 Bull Terri-
ers, both dogs with tail-chasing behavior (n = 36) and unaf-
fected dogs (24), were described by owners as having pho-
bias of common objects or situations in their environment.
Some owners reported > 1 trigger for their dog’s fearful be-
havior. Phobias were divided into 3 categories: natural envi-
ronment, social, and situational. Natural environment pho-
bias included the following: vacuums (17/60); loud noises
(8/60) including vehicles, mechanical and machinery noise,
and a noise-making doll; water (9/60) including hose water,
bath water, and rain; stairs (2/60); heights (1/60); thunder-
storms (1/60); slippery floors (5/60); mopping, sweeping,
and raking (9/60); reflective surfaces (3/60); novel house-
hold objects in environment (5/60); common household
objects out of place (5/60); moving or stationary automo-
biles (2/60); fear of own shadow (1/60); fear of outdoors
in daytime (1/60); steel doors (2/60); and doorways (1/60).
Four dogs had social phobias in the presence of people
dressed in white (1/60), strangers (1/60), people speaking
loudly (1/60), and any human contact (1/60). Ten dogs
had situational phobias involving the veterinarian’s office
(3/60), grooming shop (1/60), pet store (1/60), show ring
(1/60), elevators (1/60), crates (1/60), walks (1/60), and be-
ing away from home (1/60).
Owner-directed aggression—From the total of
333 dogs, 14 dogs with tail-chasing behavior expressed
owner-directed aggression in 5 types of interactions
with owners. Five unaffected dogs expressed owner-
directed aggression in 5 situations.
Episodic aggression—Twenty-two dogs had epi-
sodic aggression. Sixteen dogs with episodic aggression
were dogs with tail-chasing behavior, and 6 were unaf-
fected dogs. Ninety-five percent (20/21) of dogs with
episodic aggression (not observed for 1 dog with epi-
sodic aggression) went directly from a sleep state to an
attack state. All episodes were < 60 seconds in dura-
tion as described by owners. Forty-one percent (9/22)
of owners also marked situations or interactions on the
owner-directed aggression checklist that resulted in ag-
gression. In all 9 instances, aggression was reported to
be triggered by only 1 or 2 specific interactions.
Association of tail chasing with other variables—For
determination of what physical and behavioral characteristics
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were correlated with tail chasing, 10 variables were evaluated
(Table 1). Correlations (and their associated SEs) among the
10 variables were considered in the analysis. Increased risk
for developing tail chasing was not associated with coat color;
dogs with white or other color coats appeared at equal risk.
A history of tonic clonic seizures, deafness, or skin allergies
also was not associated with increased risk of developing tail
chasing, and neither was a history of shadow chasing, fly-
snapping, flank sucking, or noise sensitivity.
However, on the basis of polychoric correlations,
several behaviors were aggregated (Table 1). Tail chasing
occurred frequently with owner-directed aggression and
episodic aggression (polychoric correlations of 0.377 and
0.374, respectively). Similarly, the behavior of noise sensi-
tivity occurred frequently with episodic aggression (poly-
choric correlation of 0.644).
A log-linear model including terms for tail chasing,
episodic aggression, trance-like behavior, phobia, sex,
and owner-directed aggression ( 5 types of interactions),
along with all possible 2-way interactions, was developed
(Table 2); this model captured those variables that provid-
ed the best fit to the observed counts. Not presented is the
model with all possible 3-way interactions, none of which
proved to be significantly different from zero, a result that
was repeated across all models and submodels evaluated.
Other submodels not presented included selected 3-way
interactions; however, at no time were any of these terms
significantly different from zero.
Episodic aggression and trance-like behavior, along
with sex, had significant interactions with tail chasing
(Table 2). There was an 8% increase in tail-chasing males
(exp 0.078 = 1.081). Positive parameter estimate for the
Poisson model demonstrates that the observed frequency
of male dogs that chase their tail, as well as male dogs that
have had either episodic aggression or trance-like behav-
ior, is more common than can be explained by a model
of independent occurrence of these characteristics (ie, pa-
rameter estimates of 0.078, 0.620, and 0.883 vs –1.189,
–2.871, and –3.493, respectively). In fact, the Akaike in-
formation criterion for the model with only main effects
of tail chasing, episodic aggression, trance-like behavior,
phobia, sex, and owner-directed aggression was 200.82,
whereas the Akaike information criterion for the log-lin-
ear model was 184.84. Accordingly, the log-linear model
provided a better explanation for the observed counts of
these traits than that of an independent (ie, no interac-
tion) model. Tail-chasing behavior was more commonly
found with episodic aggression and trance-like behavior
than what would be expected given the probability of
these 3 behaviors taken individually. However, the failure
of a 3-way interaction to be significant, or for the episodic
aggression and trance-like behavior interaction to be sig-
nificant (P = 0.127), suggested that tail chasing was segre-
gated with each of these aberrant behaviors, but that epi-
sodic aggression and trance-like behavior were unrelated.
Discussion
To our knowledge, the study reported here represents
the largest study of tail chasing in Bull Terriers to date. Tail
chasing has been documented as a form of canine com-
pulsive disorder.2,7–9 Some of the previous assertions about
Variables Sex Coat Tailch Tr Phobia Noise Ownagg EA Seizures Skin
Sex 1.000 0.085 0.193 –0.200 –0.032 –0.045 0.171 –0.110 –0.182 –0.003
Coat 0.008 1.000 0.052 –0.005 0.135 –0.016 0.267 –0.006 –0.359 0.353
Tailch 0.007 0.008 1.000 0.107 0.296 0.172 0.377 0.374 0.273 0.156
Tr 0.008 0.009 0.009 1.000 0.204 0.350 0.158 0.155 0.453 0.167
Phobias 0.010 0.010 0.009 0.011 1.000 0.465 0.215 0.352 0.070 0.147
Noise 0.010 0.010 0.009 0.009 0.008 1.000 0.339 0.644 0.465 0.029
Ownagg 0.019 0.018 0.016 0.020 0.022 0.018 1.000 0.265 0.151 –0.003
EA 0.017 0.019 0.015 0.019 0.017 0.009 0.032 1.000 0.542 0.333
Seizures 0.032 0.037 0.030 0.024 0.042 0.025 0.063 0.029 1.000 0.277
Skin 0.008 0.007 0.007 0.009 0.010 0.010 0.020 0.015 0.030 1.000
Sex was scored as 1 for male and 0 for female; coat color was scored as 1 for white and 0 for color. All behaviors were scored as a 1 for yes
and 0 for no.
EA = Episodic aggression. Noise = Noise sensitivity. Ownagg = Owner-directed aggression. Seizures = Seizure events. Skin = Skin allergies.
Tailch = Tail chasing. Tr = Trance-like behavior.
Table 1—Polychoric correlation values (above the diagonal [bolded 1.000 values]) and their SEs (below the diagonal) among behavioral
and explanatory characteristics in 333 Bull Terriers (145 dogs with tail-chasing behavior and 188 unaffected dogs).
Parameter Estimate SE t value* Pr . |t|†
Intercept 1.908 0.278 6.854 0.000
Tailch 0.035 0.005 7.512 0.000
Ownagg –0.005 0.317 –0.016 0.987
EA –2.871 0.545 –5.271 0.000
Tr –3.493 0.720 –4.850 0.000
Sex –1.189 0.441 –2.698 0.010
Phobia –0.104 0.358 –0.292 0.772
Tailch X Ownagg 0.009 0.008 1.141 0.260
Tailch X EA 0.604 0.219 2.752 0.009
Tailch X Tr 1.057 0.303 3.487 0.001
Tailch X Sex 0.078 0.021 3.730 0.001
Tailch X Phobia 0.005 0.007 0.735 0.466
Ownagg X EA 0.334 0.564 0.593 0.557
Ownagg X Tr –0.226 0.535 –0.422 0.675
Ownagg X Sex 0.282 0.302 0.935 0.355
Ownagg X Phobia –0.220 0.263 –0.835 0.408
EA X Tr 1.209 0.778 1.555 0.127
EA X Sex 0.620 0.556 1.116 0.271
EA X Phobia –0.001 0.529 –0.001 0.999
Tr X Sex 0.883 0.505 1.749 0.088
Tr X Phobia 0.101 0.438 0.231 0.818
Sex X Phobia 0.257 0.302 0.851 0.399
*t value = t statistic for test. †Pr . |t| = Significance level for
test; values , 0.05 are considered significant.
See Table 1 for remainder of key.
Table 2—Parameter estimates and their SEs for the log-linear
model without consideration of overdispersion including counts
of tail chasing, episodic aggression, trance-like behavior, sex,
owner-directed aggression, and phobia, and all possible 2-way
interactions for 145 Bull Terriers with tail-chasing behavior.
888 Scientific Reports JAVMA, Vol 238, No. 7, April 1, 2011
SMALL ANIMALS/
AVIAN
this purported canine compulsive disorder were confirmed
and more closely detailed in the present study, while new
findings, in particular, increased male susceptibility and
associations of tail chasing with episodic aggression and
trance-like (staring) behaviors, were made. These conclu-
sions were based on significant interaction terms for these
behaviors with tail chasing. Interestingly, there were initial
models for this study in which owner-directed aggression
and phobias were found to have a significant interac-
tion with tail chasing. However, these initial exploratory
models did not include terms for episodic aggression or
trance-like behavior. Accordingly, overall interpretation of
the final model developed in this study suggests that al-
though owner-directed aggression and phobias had some
impact on tail chasing, trance-like behavior and episodic
aggression associate more strongly with tail chasing. This
general observation was also supported in the polychoric
correlation values (Table 1).
Our clinical perception was that many Bull Terriers
with tail-chasing behavior had mild owner-directed ag-
gression (as distinct from violent episodic aggression),
although statistical analysis indicated only a loose as-
sociation. A clinical explanation for the association of
tail chasing with owner-directed aggression may be that
increased anxiety, frustration, or conflict associated
with the performance of tail chasing or the owners’ at-
tempts to interrupt tail chasing lower the threshold for
the dogs’ aggressive response toward their owners.
The weak association between compulsive tail
chasing and phobic conditions is explicable if tail-
chasing compulsion, like human obsessive-compulsive
disorder, is regarded as an anxiety disorder.13 According
to the diagnostic manual of the American Psychiatric
Association,13 various anxiety-type disorders, including
specific phobia, social phobia, and panic disorder, are
comorbid with obsessive-compulsive disorder. Find-
ings of the study reported here suggest that a similar
association of tail-chasing compulsion and anxiety-type
disorders exists for Bull Terriers and support the bio-
logical homology concept of canine and human com-
pulsive behavior.
Although tail chasing in dogs is commonly de-
scribed as a compulsive disorder or partial seizure dis-
order,2,4,7–9 findings of the present study lead to another
possibility. Males had a slight (8%) but significantly
greater risk for developing tail chasing than females
(Table 2). Furthermore, tail chasing in Bull Terriers is
closely associated with episodic aggression and trance-
like behavior. In terms of the cluster of clinical signs
and manifestations of tail chasing, it is speculated that
this syndrome in Bull Terriers may have features in com-
mon with autism in humans. Autism is also more com-
mon in males, is associated with explosive aggression,
trance-like staring, and involves repetitive movements
and self-injurious behavior.14–16 In addition, autism is
characterized by autonomy, impaired social interac-
tions, and obsession with objects.16–18 Many owners of
Bull Terriers with tail-chasing behavior describe their
dogs as asocial, somewhat withdrawn, and abnormally
preoccupied with objects, such as balls or sticks. In-
deed, many owners use objects to redirect their dog
from tail chasing, and the dog responds to the distrac-
tion with similar intensity.
A final possible explanation for the relationship be-
tween tail chasing, trance-like behavior, and episodic
aggression is that all stem from underlying complex
partial seizures. Bull Terriers with tail-chasing behav-
ior have been shown to have epileptiform activity on
electroencephalographic recordings.4 Furthermore, vi-
olent episodic aggression in dogs has previously been
described as a seizure-related problem,19,20 and trance-
like behavior may represent a form of partial seizure in
which consciousness is altered but not lost. It is note-
worthy that epileptic seizures are reported in 4% to 32%
of humans with autism.21,22
The present study provides detailed phenotypic
and developmental information about tail chasing in
dogs and illustrates some intriguing parallels with hu-
man obsessive-compulsive disorder and possibly au-
tism. Compulsions are typically time-consuming in
clinical tail chasing and obsessive-compulsive disorder,
and the behavior seems to be performed in response to
and in order to alleviate stress. If a dog with tail-chasing
behavior or a human with obsessive-compulsive disor-
der is physically prevented from engaging in a compul-
sion, the result is mounting anxiety or tension.13 Re-
peating actions in an excessive or unreasonable manner
is a way that obsessive-compulsive disorder presents in
humans and is the primary manifestation of tail chasing
in dogs.7 In addition, the onset of tail chasing typically
occurs in young adulthood shortly before or just after
puberty. Early-life onset is also a feature of both obses-
sive-compulsive disorder and autism in humans.23,24
As with obsessive-compulsive disorder, a familial
pattern of expression of tail chasing has been described.7
Obsessive-compulsive disorder and tail chasing affect
so-called occupational or normal daily functioning and,
as shown in this study, have a detrimental effect on so-
cial activities and relationships with others. Both disor-
ders can be disruptive to overall functioning and may
lead to self-injury. Furthermore, there is comorbidity
between tail chasing and various phobias, as occurs in
obsessive-compulsive disorder. That said, over 10% of
autistic children have noise phobias and clinically di-
agnosable problems of an anxiety-related disorder, and
in addition, autism is familial in expression, with an
increased risk among siblings.24 Dogs with tail-chasing
behavior seem to be of an anxious disposition and have
been shown to respond to the same types of medica-
tions.2,25 Although there are many parallels between
canine compulsive tail chasing and human obsessive-
compulsive disorder, if tail chasing in Bull Terriers is
more closely related to autism, a new channel of trans-
lational research could be pursued relative to this com-
mon and extremely debilitating condition.
a. polycor: Polychoric and polyserial correlations, R Package, ver-
sion 07-7, R Foundation for Statistical Computing, Vienna, Aus-
tria. Available at: www.R-project.org. Accessed Jul 7, 2009.
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