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R E S E A R C H Open Access
Frequency and predisposing factors for
canine otitis externa in the UK –a primary
veterinary care epidemiological view
Dan G. O’Neill
1*
, Andrea V. Volk
2
, Teresa Soares
1
, David B. Church
3
, Dave C. Brodbelt
1
and Camilla Pegram
1
Abstract
Background: Otitis externa is a commonly diagnosed disorder in dogs and can carry a high welfare impact on
affected animals. This study aimed to report the prevalence and explore the role of breed and aural conformation
as predisposing factors for canine otitis externa in the UK. The study used a cohort design of dogs under UK
primary veterinary care at clinics participating in the VetCompass Programme during 2016. Risk factor analysis used
multivariable logistic regression modelling.
Results: The study included a random sample of 22,333 dogs from an overall population of 905,554 dogs under
veterinary care in 2016. The one-year period prevalence of otitis externa was 7.30% (95% confidence interval [CI]:
6.97 to 7.65). Breed and ear carriage were the highest ranked risk factors. Compared with crossbred dogs, sixteen
breed types showed increased odds, including: Basset Hound (odds ratio [OR] 5.87), Chinese Shar Pei (OR 3.44),
Labradoodle (OR 2.95), Beagle (OR 2.54) and Golden Retriever (OR 2.23). Four breeds showed protection (i.e.
reduced odds) of otitis externa: Chihuahua (OR 0.20), Border Collie (OR 0.34), Yorkshire Terrier (OR 0.49) and Jack
Russell Terrier (OR 0.52). Designer breed types overall had 1.63 times the odds (95% CI 1.31 to 2.03) compared with
crossbred dogs. Compared with breeds with erect ear carriage, breeds with pendulous ear carriage had 1.76 times
the odds (95% CI 1.48 to 2.10) and breeds with V-shaped drop ear carriage had 1.84 times the odds (95% CI 1.53 to
2.21) of otitis externa.
Conclusions: Breed itself and breed-associated ear carriage conformation are important predisposing factors for
canine otitis externa. Greater awareness of these associations for both predisposed and protected breeds could
support veterinary practitioners to promote cautious and low-harm approaches in their clinical advice on preventive
care for otitis externa, especially in predisposed breeds.
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* Correspondence: doneill@rvc.ac.uk
1
Pathobiology and Population Sciences, The Royal Veterinary College,
Hawkshead Lane, North Mymms, Hatfield, Herts AL9 7TA, UK
Full list of author information is available at the end of the article
Canine Medicine an
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O’Neill et al. Canine Medicine and Genetics (2021) 8:7
https://doi.org/10.1186/s40575-021-00106-1
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Plain English Summary
Otitis externa is a common and often painful condition of the ears of dogs. The probability of otitis externa varies
widely between dogs depending on their tendency towards other skin problems such as allergic skin disease.
However, breed-related anatomical features such as the degree and point of folding of the ear flap or the overall
size of the dog can act to further predispose towards otitis externa. Greater understanding of these predisposing
factors could lead to opportunities for breeders to breed away from predisposing features and also help owners
and veterinarians to predict which dogs are most at risk of this painful condition.
Veterinarians record clinical notes when dogs visit for veterinary care, and these clinical notes can act as a rich source
of information on the health of these dogs. This study accessed anonymised clinical records of almost a million dogs in
the UK to identify dogs diagnosed with otitis externa. The breed, age, bodyweight and other information available on
these dogs were used to explore why certain dog types were predisposed to otitis externa.
A random sample of 22,333 dogs was selected for analysis. Of these, 7.30% (over 7 in a hundred) were diagnosed with
otitis externa in a single year. There were 16 breeds with higher risk of otitis externa compared with crossbred dogs.
Breeds with the highest risk were Basset Hound (× 5.87), Chinese Shar Pei (× 3.44), Labradoodle (× 2.95), Beagle (× 2.54)
and Golden Retriever (× 2.23). Four breeds showed reduced risk: Chihuahua (× 0.20), Border Collie (× 0.34), Yorkshire
Terrier (× 0.49) and Jack Russell Terrier (× 0.52). Breeds with pendulous ear carriage (× 1.76) and V-shaped drop ear
carriage (× 1.84) had higher risk of otitis externa compared with breeds with erect ear carriage.
Breed itself and also breed-associated ear carriage conformation are associated with differing probability of otitis externa
in dogs. Better understanding about how these factors affect the probability of otitis externa in dogs can help veterinary
practitioners to promote cautious and low-harm approaches to preventing otitis externa (e.g., by advocating ear
cleaning with a dry paper cloth, judicious use of ear cleaners with antimicrobial properties and avoidance of overzealous
ear-cleaning) and can also assist breeders to breed away from features of dogs that predispose to otitis externa.
Keywords: VetCompass, Electronic patient record, Breed, Dog, Epidemiology, Primary-care, Purebred, Pendulous ear,
Erect ear
Background
Otitis externa describes an inflammatory state of the
outer ear canal, with or without pinnal involvement [1].
The external ear canal is lined with epithelial cells, com-
parable to the ubiquitous epidermis, with variable hair
follicles [2,3], sebaceous and ceruminous glands [4], and
is populated with a microflora [5]. All these anatomical
generalities vary widely between breeds, suggesting that
breed should be considered as an important predispos-
ing factor for otitis externa in dogs [2,6]. Otitis externa
cases present across a wide clinical spectrum, ranging
from acute inflammatory or inflammatory/infectious to
chronic cases, with or without middle ear involvement,
and may also be associated with hyperplastic or neoplas-
tic changes [7,8]. The aetiology of otitis externa cases is
generally multifactorial and has been classified according
to the PSPP-system: primary, secondary, predisposing
and perpetuating factors. Primary factors, such as aller-
gic skin disease, endocrinopathies, and keratinisation
and immune-mediated disorders, initiate inflammation/
infection of the skin and thus the ear canal, while other
primary factors such as foreign bodies can affect just the
ear canal itself. In contrast, predisposing factors on their
own, such as swimming, humidity and pinna conform-
ation, contribute to rather than initiate the otitis externa
problem. Within the pathogenesis of otitis externa,
secondary (e.g., infectious) factors and perpetuating fac-
tors (e.g., chronic changes within ear canal, tympanic
membrane and middle ear) contribute to the ongoing
pathogeneis of otitis externa [7,9]. Specific focus on pre-
disposing factors to identify both predispositions (i.e.,
higher odds) and protections (i.e. reduced odds) would
be of major interest for breeders and animal welfare sci-
entists and could lead to applications in breeding pro-
grams to lower the risk for dogs acquiring otitis externa
[10,11].
The reported prevalence of otitis externa in dogs
ranges from 8.7% [12] to 20% [8,13] in Europe, depend-
ing on the study design. Otitis externa was reported in
10.2% of dogs under primary veterinary care in the UK,
and was the most prevalent disorder overall [14]. Otitis
externa has been reported with consistently high preva-
lence in several breed-specific descriptive studies [15–
19]. However, the univariable analytical methods applied
in these studies did not allow for deeper comparison of
risk between breeds after accounting for possible con-
founding factors such as age, sex, neuter status and in-
surance [20,21]. There are few reports that explore
association between age and otitis externa [22], although
a study on 149 dogs did demonstrate differences in dis-
tribution of pathogens at different ages of onset of otitis
externa [23]. Likewise, there are limited reports
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 2 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
exploring association between sex and otitis externa, al-
though a report based on 273 dogs presenting to teach-
ing and referral hospitals in India identified higher
prevalence of otitis externa in male dogs compared to fe-
males [24].
Previously proposed predisposing factors include con-
formation of the pinna and ear canal, as well as the
numbers of hair follicles within these structures [7].
There is good evidence that exposure to moisture, for
example in dogs that regularly swim or hunt, or breeds
with anagen hair coats that are frequently bathed and
groomed, acts as a predisposing factor to water-induced,
humidity- or foreign body-related ear problems [7,25].
Other proposed predisposing factors include excessive
cerumen production (often breed related), obstructions
to the physiological air flow within the external ear
canal, alterations of the normal microflora within the
canal (e.g., due to disease, preceding therapies), irritant
iatrogenic/owner-related applications (e.g., cleaners, cot-
ton tips) and systemic debilitation (Griffin 2010). The
current study aimed to apply a quantitative methods ap-
proach based on the large volume of data available
within VetCompass to explore predisposing factors for
canine otitis externa in the UK. Breed-related aspects as
described above can act as predisposing factors promot-
ing otitis externa, even in the absence of primary sys-
temic skin diseases [7,26]. Providing evidence on breed
and conformational predisposing factors could support
the work of breeders who prioritise health in their dogs
to breed towards dog types with reduced risk of otitis
externa. Novel information on predisposing factors may
be especially relevant at the current time with the advent
of rising popularity of a range of designer breeds that
have largely unknown health status [27].
The clinical management of chronic otitis externa is
often a highly frustrating, time-consuming and expensive
endeavour between veterinary surgeon, owner and pa-
tient [28]. Improved understanding of predisposing fac-
tors in high-risk dogs should lead to better detection of
cases of otitis externa and improved owner compliance
with preventive and therapeutic care. Otitis externa is
recognised as a disorder that carries a high negative wel-
fare impact for affected dogs. A primary veterinary care
study that scored the severity of eight common disorders
in dogs ranked otitis externa as the second most severe
of these disorders [29]. Quality of life for affected dogs is
reduced by their pruritus and pain [29], but may be fur-
ther affected by uncomfortable otorrhoea, malodour,
partial to complete hearing loss, and severe pain due to
ulcerations or deeper and more marked inflammation of
middle ears and surrounding structures (e.g., temporo-
mandibular joint) [28,30–32]. Some affected dogs may
require radical surgical interventions [33]. Loss of hear-
ing and long-term low- to high-grade otic pain from
chronic otitis externa are often overlooked as an animal
welfare issue because both are unfortunately not so obvi-
ous to owners or veterinarians as are acute purulent dis-
charge, malodour or redness of the ear [30,31].
Using anonymised primary care veterinary clinical data
from the VetCompass™Programme [34], the current
study aimed to report the prevalence of diagnosis of oti-
tis externa in dogs overall and within commonly affected
breeds. The study also aimed to investigate population-
based statistical associations to explore signalment and
conformation as predisposing factors for otitis externa.
It is acknowledged that associations reported here for
predisposing factors may be complicated to differing de-
grees by additional primary, secondary and perpetuating
factors for otitis externa in some individual dogs [8,25].
This study did not aim to report on comorbidity of otitis
externa with other aural or skin disorders, or on the
clinical management or outcomes for otitis externa.
Results
Prevalence
The study included a random sample of 22,333 dogs
(2.47%) from an overall population of 905,554 dogs
under veterinary care in 2016 attending 784 veterinary
clinics participating in VetCompass. There were 1631/
22,333 otitis externa cases identified during 2016, yield-
ing a one-year period prevalence of 7.30% (95% CI:
6.97–7.65). The breed types with the highest otitis
externa prevalence were Basset Hound (28.81%, 17.76–
42.08), Chinese Shar Pei (17.76%, 11.04–26.33), Labra-
doodle (17.71%, 12.36–24.19), Beagle (14.72%, 10.09–
20.45), Golden Retriever (14.11%, 9.97–19.15) and Cock-
apoo (12.97%, 10.09–16.32). The breeds with the lowest
otitis externa prevalence were Jack Russell Terrier
(3.53%, 2.56–4.74), Yorkshire Terrier (3.27%, 2.13–4.79),
Border Collie (2.30%, 1.26–3.83) and Chihuahua (1.26%,
0.65–2.18) (Fig. 1).
Of the otitis externa cases with data available for that
variable, 1192 (73.26%) were purebred, 689 (42.32%)
were female and 820 (50.37%) were neutered. Dogs with
otitis externa had a median adult bodyweight of 17.00 kg
(IQR: 10.16–28.70, range 2.26–78.00) and median age
was 4.72 years (IQR: 2.18–8.18, range 0.23–17.70). The
most common breed types among the otitis externa
cases were Labrador Retriever (154, 9.44%), Cocker
Spaniel (81, 4.97%), Staffordshire Bull Terrier (79, 4.84%)
and Cockapoo (62, 3.80%), along with crossbred dogs
(302, 18.52%) (Tables 1and 2).
Of the dogs that were not otitis externa cases and with
data available on the variable, 15,064 (73.01%) were
purebred, 9851 (47.75%) were female and 9277 (44.97%)
were neutered. The median adult bodyweight for non-
cases was 13.43 kg (IQR: 7.98–24.65, range 1.41–85.00)
and the median age was 4.37 years (IQR: 1.85–8.04,
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 3 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
range 0.01–20.46). The most common breeds among the
non-case dogs were Labrador Retriever (1308, 6.32%),
Staffordshire Bull Terrier (1225, 5.92%), Jack Russell
Terrier (1148, 5.55%) and Chihuahua (943, 4.56%) along
with crossbred dogs (4408, 21.29%) (Tables 1and 2).
Data completeness varied between the variables assessed:
breed 99.68%, age 98.80%, sex 99.66%, neuter 99.66%
and adult bodyweight 66.82%.
Predisposing factor analysis
All tested variables except skull shape and Kennel Club
recognised breed were liberally associated with otitis
externa in univariable logistic regression modelling and
were evaluated using multivariable logistic regression
modelling as described in the methods (Tables 1and 2).
The final main breed-focused multivariable model
retained five risk factors: breed, bodyweight relative to
Fig. 1 One-year (2016) period prevalence for otitis externa in dog breeds under primary veterinary care in the VetCompass™Programme in
the UK
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 4 of 16
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Table 1 Descriptive and univariable logistic regression results for breed-related factors as predisposing factors for otitis externa
during 2016 in dogs under primary veterinary care in the VetCompass™Programme in the UK. Column percentages shown in
brackets
Variable Category Case No.
(%)
Non-case No.
(%)
Odds
ratio
95% CI
a
Category P-
value
Variable P-
value
Purebred status Crossbred 302 (18.56) 4408 (21.36) Base < 0.001
Designer 133 (8.17) 1162 (5.63) 1.67 1.35–2.07 < 0.001
Purebred 1192 (73.26) 15,064 (73.01) 1.15 1.01–1.32 0.031
Breed Crossbreed 302 (18.52) 4408 (21.29) Base < 0.001
Basset Hound 17 (1.04) 42 (0.20) 5.91 3.32–
10.50
< 0.001
Chinese Shar Pei 19 (1.16) 88 (0.43) 3.15 1.89–5.24 < 0.001
Labradoodle 31 (1.90) 144 (0.70) 3.14 2.10–4.71 < 0.001
Beagle 29 (1.78) 168 (0.81) 2.52 1.67–3.80 < 0.001
Golden Retriever 34 (2.08) 207 (1.00) 2.40 1.64–3.51 < 0.001
Cockapoo 62 (3.80) 416 (2.01) 2.18 1.63–2.91 < 0.001
English Bulldog 26 (1.59) 183 (0.88) 2.07 1.35–3.18 0.001
American Bulldog 10 (0.61) 71 (0.34) 2.06 1.05–4.03 0.036
Cavapoo 12 (0.74) 92 (0.44) 1.90 1.03–3.51 0.039
Pug 47 (2.88) 366 (1.77) 1.87 1.35–2.59 < 0.001
French Bulldog 45 (2.76) 353 (1.71) 1.86 1.34–2.59 < 0.001
West Highland White Terrier 57 (3.49) 459 (2.22) 1.81 1.34–2.44 < 0.001
Labrador Retriever 154 (9.44) 1308 (6.32) 1.72 1.40–2.11 < 0.001
Cocker Spaniel 81 (4.97) 690 (3.33) 1.71 1.32–2.22 < 0.001
Rottweiler 18 (1.10) 157 (0.76) 1.67 1.01–2.76 0.044
Bichon Frise 33 (2.02) 303 (1.46) 1.59 1.09–2.32 0.016
Boxer 22 (1.35) 223 (1.08) 1.44 0.92–2.27 0.115
English Springer Spaniel 40 (2.45) 435 (2.10) 1.34 0.95–1.89 0.094
Lhasa Apso 25 (1.53) 286 (1.38) 1.28 0.83–1.95 0.261
Cavalier King Charles Spaniel 34 (2.08) 401 (1.94) 1.24 0.86–1.79 0.258
Border Terrier 20 (1.23) 238 (1.15) 1.23 0.77–1.96 0.395
German Shepherd Dog 39 (2.39) 507 (2.45) 1.12 0.79–1.59 0.512
Shih Tzu 52 (3.19) 743 (3.59) 1.02 0.75–1.38 0.891
Other purebreds 250 (15.33) 3764 (18.18) 0.97 0.82–1.15 0.725
Staffordshire Bull Terrier 79 (4.84) 1225 (5.92) 0.94 0.73–1.22 0.643
Jack Russell Terrier 42 (2.58) 1148 (5.55) 0.53 0.38–0.74 < 0.001
Yorkshire Terrier 25 (1.53) 740 (3.57) 0.49 0.33–0.75 0.001
Border Collie 14 (0.86) 594 (2.87) 0.34 0.20–0.59 < 0.001
Chihuahua 12 (0.74) 943 (4.56) 0.19 0.10–0.33 < 0.001
Kennel Club Recognised
Breed
Not recognised 463 (28.46) 5976 (28.96) Base 0.665
Recognised 1164 (71.54) 14,658 (71.04) 1.02 0.92–1.15 0.666
Kennel Club Breed Group Breed not Kennel Club
recognised
463 (28.46) 5976 (28.96) Base < 0.001
Toy 165 (10.14) 3148 (15.26) 0.68 0.56–0.81 < 0.001
Utility 222 (13.64) 2296 (11.13) 1.25 1.06–1.47 0.009
Terrier 236 (14.51) 3412 (16.54) 0.89 0.76–1.05 0.171
Gundog 340 (20.90) 2945 (14.27) 1.49 1.29–1.73 < 0.001
Hound 71 (4.36) 727 (3.52) 1.26 0.97–1.64 0.083
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 5 of 16
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breed-sex mean,age, sex and insurance (Table 3). No
biologically significant interactions were identified. The
final model was improved by inclusion of the clinic
attended as a random effect (rho: 0.02 indicating that 2%
of the variability was accounted for by the clinic
attended, P= 0.001). The final random effects model
showed acceptable model-fit (Hosmer-Lemeshow test
statistic: P= 0.231) and acceptable discrimination (area
under the ROC curve: 0.658).
After accounting for the effects of the other variables
evaluated, 16 breeds showed increased odds of otitis
externa compared with crossbred dogs. The breed types
with the highest odds included Basset Hound (odds ratio
[OR] 5.87, 95% CI 3.26–10.57, P< 0.001), Chinese Shar
Pei (OR 3.44, 95% CI 2.04–5.78, P< 0.001), Labradoodle
(OR 2.95, 95% CI 1.96–4.46, P< 0.001), Beagle (OR
2.54, 95% CI 1.67–3.86, P< 0.001) and Golden Retriever
(OR 2.23, 95% CI 1.51–3.28, P< 0.001). Four breeds
showed reduced odds of otitis externa compared with
crossbreds: Chihuahua (OR: 0.20, 95% CI 0.11–0.36,
P< 0.001), Border Collie (OR: 0.34, 95% CI 0.19–0.58,
P< 0.001), Yorkshire Terrier (OR: 0.49, 95% CI 0.32–
0.74, P= 0.001) and Jack Russell Terrier (OR: 0.52, 95%
CI 0.37–0.72, P= 0.001). Individual dogs with an adult
bodyweight that was equal or higher than their breed/
sex mean had 1.45 (95% CI 1.29–1.63, P< 0.001) times
the odds of otitis externa compared with dogs that
weighed below their breed/sex mean. All age groups
over 1 year showed higher odds of otitis externa com-
pared with dogs aged under 1 year. Males had 1.21 times
the odds (95% CI 1.09–1.34, P< 0.001) of otitis externa
compared with females. Insured dogs had 1.34 (95% CI
1.17–1.54, P< 0.001) times the odds of otitis externa
compared with uninsured dogs (Table 3).
As described in the methods, variables derived from
the breed information individually replaced breed in the
final breed-focused model. Designer types had 1.63 times
the odds (95% CI 1.31–2.03, P< 0.001) of otitis externa
compared with crossbred dogs. Gundog (1.42 OR, 95%
CI 1.23–1.65, P< 0.001) and Utility (1.25 OR, 95% CI
1.05–1.47, P= 0.011) Kennel Club breed groups showed
higher odds of otitis externa compared with breeds that
are not recognized by the Kennel Club, while Pastoral
(0.67 OR, 95% CI 0.52–0.88, P= 0.004) and Toy (0.68
OR, 95% CI 0.56–0.81, P< 0.001) showed lower odds.
Compared with breeds with erect ear carriage, breeds
with pendulous ear carriage had 1.76 times the odds
(95% CI 1.48–2.10, P< 0.001) and dogs with V-shaped
drop ear carriage had 1.84 times the odds (95% CI 1.53–
2.21, P< 0.001) of otitis externa. Poodle types had 1.91
times the odds (95% CI 1.57–2.32, P< 0.001) of otitis
externa compared with non-poodle types. Spaniel types
Table 1 Descriptive and univariable logistic regression results for breed-related factors as predisposing factors for otitis externa
during 2016 in dogs under primary veterinary care in the VetCompass™Programme in the UK. Column percentages shown in
brackets (Continued)
Variable Category Case No.
(%)
Non-case No.
(%)
Odds
ratio
95% CI
a
Category P-
value
Variable P-
value
Pastoral 66 (4.06) 1259 (6.10) 0.68 0.52–0.88 0.004
Working 64 (3.93) 871 (4.22) 0.95 0.72–1.24 0.701
Ear carriage Erect 220 (13.49) 3898 (18.83) Base < 0.001
Semi-erect 276 (16.92) 4654 (22.48) 1.05 0.88–1.26 0.594
V-shaped drop 299 (18.33) 2734 (13.21) 1.94 1.62–2.32 < 0.001
Pendulous 395 (24.22) 3752 (18.12) 1.87 1.57–2.21 < 0.001
Variation 441 (27.04) 5664 (27.36) 1.38 1.17–1.63 < 0.001
Skull conformation Dolichocephalic 134 (8.24) 1610 (7.81) Base 0.941
Mesocephalic 754 (46.37) 9587 (46.49) 0.94 0.78–1.14 0.562
Brachycephalic 303 (18.63) 3866 (18.75) 0.94 0.76–1.16 0.578
Not categorised 435 (26.75) 5559 (26.96) 0.94 0.77–1.15 0.548
Poodle Not poodle-type 1188 (72.84) 15,302 (73.92) Base < 0.001
Poodle-type 137 (8.40) 924 (4.46) 1.91 1.58–2.31 < 0.001
Not categorised 306 (18.76) 4476 (21.62) 0.88 0.77–1.00 0.055
Spaniel Non spaniel-type 1152 (70.63) 14,539 (70.23) Base < 0.001
Spaniel-type 173 (10.61) 1687 (8.15) 1.29 1.09–1.53 0.003
Not categorised 306 (18.76) 4476 (21.62) 0.86 0.76–0.98 0.027
a
CI confidence interval
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 6 of 16
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Table 2 Descriptive and univariable logistic regression results for non-breed-related signalment factors as predisposing factors for otitis externa
during 2016 in dogs under primary veterinary care in the VetCompass™Programme in the UK. Column percentages shown in brackets
Variable Category Case No.
(%)
Non-case No.
(%)
Odds
ratio
95% CI
a
Category P-
value
Variable P-
value
Adult (> 18 months) bodyweight
(kg)
< 10.0 299 (18.33) 5115 (24.71) Base < 0.001
10.0 - < 15.0 261 (16.00) 2203 (10.64) 2.03 1.70–
2.41
< 0.001
15.0 - < 20.0 144 (8.83) 1550 (7.49) 1.59 1.29–
1.95
< 0.001
20.0 - < 25.0 143 (8.77) 1461 (7.06) 1.67 1.36–
2.06
< 0.001
25.0 - < 30.0 116 (7.11) 1234 (5.96) 1.61 1.29–
2.01
< 0.001
30.0 - < 40.0 194 (11.89) 1575 (7.61) 2.11 1.74–
2.55
< 0.001
≥40.0 80 (4.90) 549 (2.65) 2.49 1.92–
3.24
< 0.001
Unavailable 394 (24.16) 7015 (33.89) 0.96 0.82–
1.12
0.612
Bodyweight relative to breed mean Lower 560 (34.33) 7486 (36.16) Base < 0.001
Equal/Higher 673 (41.26) 6155 (29.73) 1.46 1.30–
1.64
< 0.001
Unavailable 398 (24.40) 7061 (34.11) 0.75 0.66–
0.86
< 0.001
Age (years) < 1.0 years 116 (7.11) 2392 (11.55) Base < 0.001
1.0 - < 2.0 years 251 (15.39) 3027 (14.62) 1.71 1.36–
2.14
< 0.001
2.0 - < 4.0 years 347 (21.28) 4111 (19.86) 1.74 1.40–
2.16
< 0.001
4.0 - < 6.0 years 258 (15.82) 3195 (15.43) 1.67 1.33–
2.09
< 0.001
6.0 - < 8.0 years 225 (13.80) 2573 (12.43) 1.80 1.43–
2.27
< 0.001
8.0 - < 10.0
years
179 (10.97) 2069 (9.99) 1.78 1.40–
2.27
< 0.001
10.0 - < 12.0
years
132 (8.09) 1441 (6.96) 1.89 1.46–
2.44
< 0.001
≥12.0 years 109 (6.68) 1641 (7.93) 1.37 1.05–
1.79
0.22
Unavailable 14 (0.86) 253 (1.22) 1.14 0.65–
2.02
0.650
Sex Female 689 (42.24) 9851 (47.58) Base < 0.001
Male 939 (57.57) 10,779 (52.07) 1.25 1.12–
1.38
< 0.001
Unavailable 3 (0.18) 72 (0.35) 0.60 0.19–
1.90
0.380
Neuter Entire 808 (49.54) 11,353 (54.84) Base < 0.001
Neutered 820 (50.28) 9277 (44.81) 1.24 1.12–
1.37
< 0.001
Unavailable 3 (0.18) 72 (0.35) 0.59 0.18–
1.86
0.365
Insurance Non-insured 1329 (81.48) 18,025 (87.07) Base < 0.001
Insured 302 (18.52) 2677 (12.93) 1.53 1.34–
1.75
< 0.001
a
CI confidence interval
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 7 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Table 3 Final breed-focused mixed effects multivariable logistic regression model for predisposing factors associated with otitis
externa in dogs under primary veterinary care in the VetCompass™Programme in the UK. Clinic attended was included as a random
effect
Variable Category Odds ratio 95% CI
a
P-value
Breed Crossbreed Base
Basset Hound 5.87 3.26–10.57 < 0.001
Chinese Shar Pei 3.44 2.04–5.78 < 0.001
Labradoodle 2.95 1.96–4.46 < 0.001
Beagle 2.54 1.67–3.86 < 0.001
Golden Retriever 2.23 1.51–3.28 < 0.001
Cockapoo 2.22 1.65–3.00 < 0.001
American Bulldog 2.16 1.09–4.26 0.027
French Bulldog 2.11 1.50–2.96 < 0.001
English Bulldog 2.08 1.35–3.21 0.001
Pug 1.95 1.40–2.72 < 0.001
Cavapoo 1.92 1.03–3.59 0.040
West Highland White Terrier 1.72 1.27–2.34 < 0.001
Rottweiler 1.67 1.01–2.77 0.047
Cocker Spaniel 1.67 1.29–2.17 < 0.001
Labrador Retriever 1.64 1.33–2.01 < 0.001
Bichon Frise 1.49 1.02–2.18 0.042
Boxer 1.40 0.89–2.22 0.149
English Springer Spaniel 1.24 0.88–1.76 0.226
Lhasa Apso 1.23 0.80–1.89 0.351
Border Terrier 1.15 0.71–1.85 0.571
German Shepherd Dog 1.13 0.80–1.61 0.482
Cavalier King Charles Spaniel 1.13 0.78–1.64 0.518
Shih Tzu 1.00 0.73–1.36 0.986
Other purebreds 0.96 0.80–1.14 0.625
Staffordshire Bull Terrier 0.95 0.73–1.23 0.678
Jack Russell Terrier 0.52 0.37–0.72 < 0.001
Yorkshire Terrier 0.49 0.32–0.74 0.001
Border Collie 0.34 0.19–0.58 < 0.001
Chihuahua 0.20 0.11–0.36 < 0.001
Bodyweight relative to breed mean Lower Base
Equal/Higher 1.45 1.29–1.63 < 0.001
Unavailable 0.80 0.69–0.93 0.003
Age (years) < 1.0 years 1.00
1.0 - < 2.0 years 1.56 1.24–1.97 < 0.001
2.0 - < 4.0 years 1.43 1.13–1.80 0.003
4.0 - < 6.0 years 1.38 1.08–1.76 0.010
6.0 - < 8.0 years 1.47 1.14–1.89 0.003
8.0 - < 10.0 years 1.45 1.11–1.88 0.006
10.0 - < 12.0 years 1.57 1.19–2.07 0.001
> or = 12.0 years 1.22 0.92–1.63 0.171
No age available 1.44 0.80–2.58 0.220
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 8 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Table 3 Final breed-focused mixed effects multivariable logistic regression model for predisposing factors associated with otitis
externa in dogs under primary veterinary care in the VetCompass™Programme in the UK. Clinic attended was included as a random
effect (Continued)
Variable Category Odds ratio 95% CI
a
P-value
Sex Female Base
Male 1.21 1.09–1.34 < 0.001
Unrecorded 0.78 0.24–2.54 0.683
Insurance Uninsured Base
Insured 1.34 1.17–1.54 < 0.001
a
CI Confidence interval
Table 4 Results for risk factors that directly replaced the breed variable in the final breed-focused mixed effects multivariable logistic
regression model (along with age, bodyweight relative to breed mean, sex and insurance status). Adult (> 18 months) bodyweight
(kg) replaced the breed and bodyweight relative to breed mean variables in the final breed-focused mixed effects multivariable
logistic regression model. These results report associations between these predisposing factors and otitis externa in dogs under
primary veterinary care in the VetCompass™Programme in the UK. Clinic attended was included as a random effect
Variable Category Odds ratio 95% CI
a
Category P-value
Purebred status Crossbred Base
Designer 1.63 1.31–2.03 < 0.001
Purebred 1.13 0.99–1.29 0.060
Kennel Club Breed Group Breed not Kennel Club recognised Base
Toy 0.68 0.56–0.81 < 0.001
Utility 1.25 1.05–1.47 0.011
Terrier 0.88 0.75–1.04 0.143
Gundog 1.42 1.23–1.65 < 0.001
Hound 1.23 0.94–1.60 0.128
Pastoral 0.67 0.52–0.88 0.004
Working 0.94 0.72–1.24 0.672
Ear carriage Erect Base
Semi-erect 1.03 0.86–1.24 0.757
V-shaped drop 1.84 1.53–2.21 < 0.001
Pendulous 1.76 1.48–2.10 < 0.001
Variation 1.36 1.15–1.60 < 0.001
Poodle Not poodle-type Base
Poodle-type 1.91 1.57–2.32 < 0.001
Not categorised 0.90 0.79–1.03 0.117
Spaniel Non spaniel-type Base
Spaniel-type 1.24 1.05–1.47 0.013
Not categorised 0.88 0.77–1.00 0.054
Adult (> 18 months) bodyweight (kg) < 10.0 Base
10.0 - < 15.0 1.97 1.66–2.35 < 0.001
15.0 - < 20.0 1.58 1.28–1.94 < 0.001
20.0 - < 25.0 1.65 1.34–2.04 < 0.001
25.0 - < 30.0 1.59 1.27–1.99 < 0.001
30.0 - < 40.0 2.05 1.69–2.48 < 0.001
≥40.0 2.35 1.80–3.07 < 0.001
Unavailable 0.99 0.83–1.17 0.874
a
CI Confidence interval
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 9 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
had 1.24 times the odds (95% CI 1.05–1.47, P= 0.013) of
otitis externa compared with non-spaniel types. Dogs
weighing under 10 kg had lower odds of otitis externa
than all other categories with higher bodyweight. Skull
shape was not associated with otitis externa (Table 4).
Discussion
This is the largest study of dogs under primary veterin-
ary care to date that provides epidemiological evidence
on the frequency of diagnosis of otitis externa and its
predisposing factors. Following some prior published
evidence [8,26,35], the current study explored the odds
of otitis externa between canine breeds with differing
forms of ear carriage as a predisposing factor. In this ra-
ther large current cohort of cases, our results show that
breeds with pendulous pinnal carriage had 1.76 times
the odds of otitis externa compared with breeds with
erect carriage. However, the results also provided some
novel insights to show that dogs with V-shaped drop
pinna have similar risk of otitis externa as breeds with
pendulous ears (OR 1.84). Conversely, no difference in
odds was detected between dogs with erect compared to
dogs with semi-erect pinnae. Pendulous pinnal carriage
has long been reported as a predisposing factor for otitis
externa [8,26,35] with the suggestion that this con-
formation can result in heat and moisture retention
within the ear canal [26] and may be more likely to re-
tain foreign material than other ear carriage types
(Griffin 2010, Miller 2013). However, the identification
of V-shaped drop pinna as a predisposing factor for oti-
tis externa with a similar effect to pendulous ears is a
novel finding. Future studies to explore possible differ-
ences between the pathogenetic pathways for otitis
externa in pendulous and V-shaped pinnal conforma-
tions are warranted, particularly to link this novel pre-
disposing factor information with primary (e.g., allergic,
endocrine, foreign bodies), secondary (variability of in-
fectious agents) and perpetuating (such as otitis media,
chronic tympanic membrane and external canal
changes) factors [8]. It should be noted that ear carriage
and breed are closely linked concepts and therefore it is
challenging to unravel the relative contributions of pre-
disposing factors (such as ear carriage) from primary fac-
tors (such as allergic dermatitis) in breeds with a
propensity to both. Hence the current study took a
quantitative study design approach with multivariable
modelling to report overall effects of predisposing fac-
tors at a population level but acknowledges that there
will be additional nuance at the individual animal level
that breeders, welfare scientists and veterinarians will
need to additionally consider. However, notwithstanding
these considerations about crossover of effects between
differing PSPP factors, the current study provides strong
epidemiological evidence that pinnal carriage per se acts
as a predisposing factor for otitis externa. This informa-
tion could support the Kennel Club Breed Health and
Conservation Plans, which aims to identify, prioritise
and advise on breed health concerns [11].
After accounting for confounding effects, Basset
Hound (OR 5.87), Chinese Shar Pei (OR 3.44), Labra-
doodle (OR 2.95), Beagle (OR 2.54) and Golden Re-
triever (OR 2.23) had the highest odds of otitis externa
compared with crossbreeds. Basset Hounds have previ-
ously been reported at higher risk of otitis externa due
to their highly pendulous pinnae, a phenotype that was
selected supposedly to lead scents to their noses [36,37].
Although without a firm evidence base, it is also possible
that the long and deep ear canal in Basset Hounds may
also act to delay resolution of infections once started,
and lead to higher probability of otic chronicity in this
breed. The current study reported prevalence (i.e. the
proportion of dogs diagnosed at least once during the
study year) but did not take direct account of the sever-
ity or duration of these clinical events [29]. Basset
Hounds are reported to harbour more Malassezia spp.
yeasts on their skin, including within the ear canal, com-
pared with toy breeds [38]. This may manifest clinically
as dark staining of the skin with or without discharge in
their ear canals and skin folds and can be verified by cy-
tology [39,40]. However, without accompanying ery-
thema and/or pruritus, this presentation should not
necessarily lead to a diagnosis of otitis externa [38]. This
highlights the importance of thorough examination of
the ear canal in combination with the pinna (and the
overall body skin) as well as assessing for clinical signs
(e.g., pruritus, head shaking) on the path of the decision-
making process towards a diagnosis of otitis externa.
Beagles and Golden Retrievers have dropped (pendulous
or V-shaped) pinnae which, as identified in the current
study, may increase the risk of these breeds for otitis
externa [41]. Chinese Shar Pei, however, have semi-erect
ears, suggesting an alternative pathogenesis in this breed.
Following selective breeding to achieve the Chinese Shar
Pei breed standard, hyaluronic acid accumulates in their
dermis resulting in folded and narrowed ear canals, pre-
dominantly of the vertical part [42–44]. Breed health
plans for breeds at high risk of otitis externa could con-
sider prioritising control of otitis externa as a priority
health goal [11] while owners and veterinarians should
be especially vigilant about ear examination and care in
such predisposed breeds.
For the first time, we report here on protection (i.e. re-
duced odds) for otitis externa in the Chihuahua (OR
0.20), Border Collie (OR 0.34), Yorkshire Terrier (0.49)
and Jack Russell Terrier (0.52). To date, the veterinary
literature has focused mainly on breed predisposition to
disease [45]. However, there is an increasing awareness
of the value of exploring protection to disorders within
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 10 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
breeds with a view to elucidating novel genetic, con-
formational and aetiopathogenetic pathways for reduced
disorder occurrence [10,21]. Discovery of protected
breeds could also support plans to improve breed health
and reduce disorder incidence in at-risk breeds by out-
crossing programmes [46,47]. Chihuahua was the breed
with the lowest risk to otitis externa, potentially due, in
part, to their erect pinnal conformation [8,41], low body
weight (smallest dog breed) and low tendency to primary
skin disease in general [48]. The presence of guard hairs at
the entrance to the ear canal in Chihuahuas may also con-
tribute to a low risk of otitis externa. However, there is
controversy about whether guard hairs act more to protect
ear canals from the ingress of foreign material or to pre-
vent the egress of foreign material from the ear canal. Pre-
venting egress would likely delay resolution of otitis
externa. For example, although German Shepherd Dog
and Siberian Husky breeds both have plentiful guard hairs
at the entrance of the ear canal, the former appears to be
more often affected by otitis externa than the latter, sug-
gesting that the role of guard hairs in otitis externa may
be quite complex [49]. Other than Border Collies, it is not-
able that the breeds identified as significantly protected
were all small breed dogs, suggesting that small body size
and therefore shorter ear canals [4]inadditiontopinnal
conformation may be contributory protective factors [41].
The current study is one of the first to explore dis-
order occurrence across a range of designer breed-types.
A hybrid vigour effect has been previously proposed
whereby designer dogs with greater outbreeding are ex-
pected to show better general health than pedigree dogs
that are more inbred [50]. However, this effect is not
supported by the current study for a polygenic disorder
such as otitis externa where some common designers
types even showed predispositions to increased disorder
risk. Designer breeds overall showed 1.63 times the odds
of otitis externa compared with crossbreeds. The higher
odds identified may be less to do with being designer
per se and more to do with the poodle or spaniel com-
ponent that is common among popular designer types.
In line with this, Labradoodles (OR 2.95), Cockapoos
(OR 2.22) and Cavapoos (OR 1.92) were all identified at
greater risk of otitis externa compared with crossbreeds.
Poodle-types (OR 1.91) showed greater risk of otitis
externa compared with non-poodle types while spaniel-
types (OR 1.24) had greater risk than non-spaniel types.
Increased risk for otitis externa in poodles may in part
be due to their pendulous pinnal carriage, excessive
curly hairs in the external ear canal [1,26,51], aural
microclimate and the proposed need for repeated ear
plucking that is under heavy controversy [25]. In
addition, poodles are commonly affected by allergic skin
disease that can act as a primary cause of otitis externa
[52] and especially prone to Malassezia overgrowth in
the ear canals [22]. The poodle breed itself is a water
hound which enhances the behavior trait for excessive
swimming, thus a higher likelihood of moist ear canals
and Swimmer’s ear [25]. This poodle predisposition may
even be increased by crossing a poodle with a spaniel
which is another predisposed breed type with pendulous
pinnal carriage, or with a breed such as the Labrador Re-
triever that is prone to primary skin disease contributing
to aural atopic disease [53–55]. Therefore, breeders of
designer-types need to be wary to avoid selecting to-
wards a phenotype that combines differing risk factors
from parental breeds and therefore could increase dis-
ease risk in the first generation of puppies (often called
the F1 hybrids) [56,57]. The wider variability in the phe-
notypes of progeny from planned hybridisation between
different breeds may also lead to greater variability in
the health status across individual dogs from these hy-
bridisation breeding programmes.
It is worth noting that the current study was based on
dogs that are under veterinary care in the UK [34]. In
consequence, these dogs reflect the wider dog popula-
tion of the UK but there may be differences in the typ-
ical conformations between the estimated subsets of
around 30% within breeds that are registered with The
Kennel Club and the remaining estimated 70% that are
not registered with The Kennel Club [58]. Similarly,
there may be variation in typical breed conformations,
genetics and canine lifestyle factors between countries
and therefore extrapolation of the results in the current
paper should be taken cautiously [59–61].
Bodyweight was identified as a predisposing factor for
otitis externa, with dogs weighing over 40 kg at greatest
risk of otitis externa (OR 2.35) compared with dogs
under 10 kg. Breed and bodyweight are highly correlated,
therefore these two factors were not included in the
same models [62]. However, this increased risk with in-
creasing absolute bodyweight is also reflected in the
current results by an increased risk in higher weight-
carrying dogs within the same breed. Dogs weighing at
or above the breed mean bodyweight had 1.45 times the
odds of otitis externa compared with those weighing
below. It is possible that increased risk of otitis externa
in heavier dogs may in part be related to obesity and
neutering state, but further studies are needed to eluci-
date this mechanism more fully. Nonetheless, these sug-
gestive findings that obesity may be linked to higher
odds of otitis externa should further promote the im-
portance of maintaining a moderate body condition
score in dogs [63].
Sex was identified as a weak but still predisposing fac-
tor for otitis externa in the current study, with males at
1.21 times the odds of otitis externa compared with fe-
males. A report based on 273 dogs presenting to teach-
ing and referral hospitals in India similarly identified
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 11 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
higher prevalence of otitis externa in male dogs com-
pared to females [24]. Several UK breed-based reports
failed to identify sex-related differences for otitis externa
[15,17,55,64]. However, a significantly higher preva-
lence of otitis externa in males compared to females has
been reported in the West Highland White Terrier [16]
and Chihuahua [65]. Androgen hormones may increase
sebum production, which is a predisposing factor to flare
up of latent otic infections as well as favouring Malasse-
zia spp. overgrowth. Conversely, oestrogens elicit an op-
posite response of drying the skin that may promote
secondary infections, especially in allergic dermatitis
cases [7,24,25]. The current study provides some evi-
dence of an increased risk in males overall but further
research is required to determine if this is universal
across breeds or whether this effect varies between
breeds and is moderated by other factors.
No substantial associations were identified between
variants of skull conformation and otitis externa in the
current study. Some increased risk may have been ex-
pected in brachycephalic breeds from a biological per-
spective because the external ear canal of brachycephalic
dogs is often folded and narrowed due to the skull
shape, which would be expected to promote reduced air
flow and increased humidity in the ear canal, thus pro-
moting and prolonging otitis externa [66]. Consistent
with this rationale, the current study showed that breeds
with more extreme brachycephaly, such as French Bull-
dogs, English Bulldogs and Pugs, had greater odds of oti-
tis externa than crossbreeds. There is conformational
variation both within, and between, brachycephalic breeds
[67] and therefore it may be that skull shape acts as a pre-
disposing factor only for the more extreme brachycephalic
breed types. This effect may act as another reason to sup-
port the increasing calls to reduce the degree of extreme
exaggeration in many brachycephalic breeds [68,69].
This study focused on predisposing factors that centre
on breed and other demographic characteristics. This
epidemiological approach is in line with the critical data
gaps on population-based breed prevalence predisposi-
tions that have been identified especially over the past
15 years in relation to improving the genetic health of
purebred dogs [70–72]. The current study aims to build
on an expanding literature on breed-related studies that
are filling this data gap [21,73–76] and that are support-
ing reforms to breed health such as The Kennel Club’s
Breed Health and Conservation Plans project [11]. How-
ever, there are other categories of risk factors that could
have also been considered and that would have added
additional useful inference from other perspectives.
There is little information available at a population level
about the relative proportional contributions of other
underlying conditions (e.g., atopic dermatitis, aural for-
eign body) to the overall disorder burden from otitis
externa. Exploration of the comorbid presence of a range
of potential clinical risk factors in each of the otitis
externa cases in the current dataset could provide some
information on the relative importance of each of these
to the overall occurrence of otitis externa in dogs and
therefore constitutes a useful concept for future study
[74]. Extraction of detailed data on veterinary clinical
management and therapy offers another research ap-
proach that could build on the current data to contrib-
ute to a deeper understanding of the pathophysiology of
these otitis externa cases at a population level [77]. Elu-
cidation of proportional usage of antibiosis, for example,
could provide evidence of a bacterial role in the otitis
externa process while evidence from bacterial culture
and antimicrobial sensitivity testing could provide dee-
per insights into the most commonly associated bacteria
and their common antibiograms [78,79]. There is also
currently high interest in exploring aspects related to
antimicrobial stewardship in companion animals and
therefore benchmarking of current first opinion thera-
peutic patterns to offer additional scientific benefits [75,
80]. A deeper understanding of breed as a risk factor for
otitis externa could take into account the severity of the
disorder phenotype experienced by these dogs as well as
a range of temporal characteristics including the dur-
ation of individual events, recurrence and chronicity.
Analysis of these features has been applied previously to
compare welfare impact across common disorders in
dogs but this approach could also be taken to compare
between breeds in future studies [29].
Research based on primary-care data offers novel op-
portunities to better understand common and less com-
plicated disorders [14] but the methodology does have
some important limitations which have been previously
documented [14,81]. In addition to these, the current
study may have under-estimated the true prevalence of
otitis externa because some owners of affected dogs may
not have sought veterinary attention e.g., for financial
reasons: this possibility is suggested by higher odds of
otitis externa in insured dogs in the current study. Add-
itionally, some owners may not have acknowledged the
existence of otitis externa in their dog because of limited
awareness of the clinical signs or the welfare significance
of aural pain and hearing alterations [28–31]. Dissemin-
ation of information from veterinarians on the need for
increased aural vigilance by owners of breeds with
known predisposing factors for otitis externa may there-
fore assist with earlier recognition and higher levels of
presentation for veterinary care of affected dogs. Add-
itional breeds to the ones included in the current study
have previously been reported with predisposition to oti-
tis externa [8,82] but there were insufficient numbers
for many of these rarer breeds in the current study for
reliable assessment.
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 12 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Conclusions
This large study using primary-care veterinary data re-
ports a 7.30% prevalence for otitis externa in dogs in the
UK, highlighting the importance of otitis externa to ca-
nine welfare and clinical caseloads. Conformational pre-
dispositions were identified, with dogs with pendulous
and V-shaped drop pinnal carriage at higher risk of otitis
externa than dogs with erect pinnal carriage. Strong
breed effects as predisposing factors were identified, with
Basset Hound, Chinese Shar Pei, Labradoodle, Beagle
and Golden Retriever showing greatest predisposition to
otitis externa. In addition, designer breed types had
higher odds of otitis externa compared with crossbreeds.
Awareness of these risk factors could assist veterinary
practitioners and owners to reduce the contribution of
aural disorders to the overall welfare burden in dogs by
improved selection of dogs for breeding and ownership,
and by earlier recognition of clinical events of otitis
externa. Greater understanding on how breed itself and
breed-associated ear carriage conformation factors affect
the probability of otitis externa in dogs can help veterin-
ary practitioners to promote cautious and low-harm ap-
proaches to preventing otitis externa (e.g., by advocating
ear cleaning with a dry paper cloth, judicious use of ear
cleaners with antimicrobial properties and avoidance of
overzealous ear-cleaning) and can also assist breeders to
breed away from features of dogs that predispose to oti-
tis externa. Owners can be encouraged to regularly
check their dog’s ears for malodour and exudate, and
veterinarians can follow up by otoscopy and cytological
examination. Breed health plans could consider inclu-
sion of otitis externa as a priority condition in predis-
posed breeds and conformations.
Methods
The study population included all dogs under primary
veterinary care at clinics participating in the VetCom-
pass Programme during 2016. Dogs under veterinary
care were defined as having either a) at least one elec-
tronic patient record (EPR) (free-text clinical note, treat-
ment or bodyweight) recorded during 2016 or b) at least
one EPR recorded during both 2015 and 2017. VetCom-
pass collates de-identified EPR data from primary-care
veterinary practices in the UK for epidemiological re-
search [34]. Data fields available to VetCompass re-
searchers include a unique animal identifier along with
species, breed, date of birth, sex, neuter status and insur-
ance. Clinical information from free-form text clinical
notes, summary diagnosis terms [83], bodyweights and
treatment with relevant dates were also available.
A cohort study design was used to estimate the one-
year (2016) period prevalence of otitis externa and to ex-
plore associations with signalment and conformation as
predisposing factors. Sample size calculations estimated
that 13,621 dogs would need to be assessed to estimate
prevalence for a disorder occurring in 10.0% of dogs [84]
with 0.5% acceptable margin of error at a 95% confi-
dence level from a population of 905,544 dogs [85]. Eth-
ics approval was obtained from the RVC Ethics and
Welfare Committee (reference SR2018–1652).
The case definition for otitis externa cases required
evidence in the clinical records that otitis externa was
diagnosed to exist as a clinical condition at some point
during 2016. The clinical decision-making process was
completely at the discretion of the attending veterinary
surgeons. The clinical records of a randomly selected
subset of dogs from the sampling frame of unique dogs
in the overall study population were reviewed manually
in detail to identify all dogs that met the case definition
for otitis externa [84]. This study aimed to identify and
extract information on the diagnosed cases rather than
to question how these diagnoses were made. No add-
itional information was extracted on laterality, chronicity
or comorbidity with other conditions. No distinction
was made between pre-existing and incident cases of oti-
tis externa.
Breed descriptive information entered by the partici-
pating practices was cleaned and mapped to a VetCom-
pass breed list derived and extended from the VeNom
Coding breed list that included both recognised pure-
bred breeds and also designer breed terms [83]. A pure-
bred variable categorised all dogs of recognisable breeds
as ‘purebred’, dogs with contrived breed names gener-
ated from two or more purebred breed terms as de-
signers (e.g., Labradoodle) and all remaining dogs with
breed information as ‘crossbred’[59]. A breed variable
included individual pure breeds and designers repre-
sented by over 300 dogs in the overall study population
or with ≥10 otitis externa cases, a grouped category of
all remaining purebreds and a grouping of general cross-
bred dogs. This approach was taken to facilitate statis-
tical power for the individual breed analyses [86].
Crossbreeds were used as the comparator group because
they were the largest single group.
Breeds were characterised by ear carriage based on
pinnal phenotypes typically described for each breed [60,
87,88]. The categories of ear carriage included erect
(also known as prick or upright e.g., German Shepherd
Dog), semi-erect (also known as cocked or semi-pricked
e.g., Rough Collie), V-shaped drop (also known as folded
e.g., Hungarian Vizsla), pendulous (also known as drop
or pendant, e.g., Basset Hound) and unspecified. Based
on various kennel club breed descriptions [59,89],
breeds were also characterised by skull shape (dolicho-
cephalic, mesocephalic, brachycephalic, not categorised),
spaniel (spaniel, non-spaniel, not categorised) and poo-
dle (poodle, non-poodle, not categorised) status for ana-
lysis. Crossbreds were classified as ‘not categorised’for
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 13 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
these variables. A Kennel Club breed group variable clas-
sified breeds recognised by the UK Kennel Club into
their relevant breed groups (Gundog, Hound, Pastoral,
Terrier, Toy, Utility and Working) and all remaining
types were classified as non-Kennel Club recognised
[59].
Neuter and insurance status were defined by the final
available EPR value. Adult bodyweight was defined as
the mean of all bodyweight (kg) values recorded for each
dog after reaching 18 months old and was categorised as:
< 10.0, 10.0 to < 15.0, 15.0 to < 20.0, 20.0 to < 25.0, 25.0
to < 30.0, 30.0 to < 40.0 and ≥40.0. Mean adult body-
weight was generated for all breed/sex combinations
with adult bodyweight available for at least 100 dogs in
the overall study population and used to categorise indi-
vidual dogs as “at or above the breed/sex mean”,“below
the breed/sex mean”and “no recorded bodyweight”. Age
(years) was defined at December 31, 2016 and was cate-
gorised as: ≤1.0, 1.0 to < 2.0, 2.0 to < 4.0, 4.0 to < 6.0,
6.0 to < 8.0, 8.0 to < 10.0, 10.0 to < 12.0 and ≥12.0.
Following internal validity checking and data cleaning
in Excel (Microsoft Office Excel 2013, Microsoft Corp.),
analyses were conducted using Stata Version 13 (Stata
Corporation).
One-year period prevalence values with 95% confi-
dence intervals (CI) described the probability of diagno-
sis at least once during 2016 in dogs overall and in
common breeds. The CI estimates were derived from
standard errors based on approximation to the binomial
distribution [90]. Predisposing factor analysis included
dogs with otitis externa as cases and all remaining dogs
as non-cases. Binary logistic regression modelling was
used to evaluate univariable associations between risk
factors of interest as potential predisposing factors and
also factors that were included to account for confound-
ing (breed, ear carriage, skull shape, spaniel, poodle,
purebred, Kennel Club recognised breed, Kennel Club
breed group, adult bodyweight, bodyweight relative to
breed/sex mean, age, sex, neuter and insurance) with an
outcome variable of otitis externa during 2016. Because
breed was a factor of primary interest as a predisposing
factor, variables derived from breed information were
considered as correlated with breed (ear carriage, skull
shape, spaniel, poodle, purebred, Kennel Club recognised
breed and Kennel Club breed group) and were excluded
from initial breed multivariable modelling. Instead, each
of these variables individually replaced the breed variable
in the main final breed-focused model to evaluate their
effects after taking account of the other variables. Adult
bodyweight (a defining characteristic of individual
breeds) replaced breed and bodyweight relative to breed/
sex mean in the final breed-focused model. Risk factors
with liberal associations in univariable modelling
(P< 0.2) were taken forward for multivariable
evaluation. Model development used manual backwards
stepwise elimination. Clinic attended was evaluated as a
random effect and pair-wise interaction effects were
evaluated for the final model variables [20]. The area
under the ROC curve and the Hosmer-Lemeshow test
were used to evaluate the quality of the model fit and
discrimination (non-random effect model) [20,91]. Stat-
istical significance was set at P< 0.05.
Abbreviations
CI: Confidence interval; EPR: Electronic patient record; IQR: Interquartile
range; KC: The Kennel Club; OR: Odds ratio
Acknowledgements
Thanks to Noel Kennedy (RVC) for VetCompass™software and programming
development. We are grateful to the following researchers who assisted with
data collection during this project: Alice Ashworth, Alison Toetz, Bethany
Allen, Eleanor White, Elizabeth Ainsworth, Jasmine Broomhead, Joanne
Humphrey and Penelope Crocker. We acknowledge the Medivet Veterinary
Partnership, Vets4Pets/Companion Care, Goddard Veterinary Group, CVS
Group, IVC Evidensia, Linnaeus Group, Beaumont Sainsbury Animal Hospital,
Blue Cross, PDSA, Dogs Trust, Vets Now and the other UK practices who
collaborate in VetCompass™. We are grateful to The Kennel Club Charitable
Trust, Agria Pet Insurance and The Kennel Club for supporting VetCompass™.
Authors’contributions
DON was responsible for the conception and design, acquisition, extraction
and analysis of data. TS assisted with data extraction. DON, AVV and TS were
mainly responsible for drafting the manuscript. DON, AVV, TS, CP, DC and DB
were involved in interpreting the results, revising the manuscript and gave
final approval of the version to be published. DON, AVV, TS, CP, DC and DB
agree to be accountable for all aspects of the accuracy and integrity of the
work.
Funding
This study was supported at the RVC by an award from the Kennel Club
Charitable Trust and Agria Pet Insurance. The Kennel Club Charitable Trust,
Agria Pet Insurance or The Kennel Club had no input in the design of the
study, the collection, analysis and interpretation of data or in writing the
manuscript.
Availability of data and materials
The datasets generated during and/or analysed during the current study are
available at the RVC Research Online repository https://researchonline.rvc.ac.
uk/id/eprint/13333
Declarations
Ethics approval and consent to participate
Ethics approval was granted by the RVC Ethics and Welfare Committee
(reference number reference SR2018–1652).
Consent for publication
The study has full consent for publication of all the information used.
Competing interests
The authors have no competing interests to declare.
Author details
1
Pathobiology and Population Sciences, The Royal Veterinary College,
Hawkshead Lane, North Mymms, Hatfield, Herts AL9 7TA, UK.
2
Department of
Small Animal Medicine and Surgery, University of Veterinary Medicine
Hannover, Foundation, Buenteweg 9, 30559 Hannover, Germany.
3
Clinical
Science and Services, The Royal Veterinary College, Hawkshead Lane, North
Mymms, Hatfield, Herts AL9 7TA, UK.
O’Neill et al. Canine Medicine and Genetics (2021) 8:7 Page 14 of 16
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Received: 9 May 2021 Accepted: 3 August 2021
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