American Cocker Spaniels (ACSs) develop aural ceruminous gland hyperplasia and ectasia more often than dogs of other breeds. Data on the cause and development of these breed characteristic histopathological changes are lacking. We performed video-otoscopic examinations and dermatological work-up on 28 ACSs, obtained aural biopsies from each dog and assessed the statistical associations between the presence of ceruminous gland hyperplasia and ectasia and disease history, clinical or microbiological findings and underlying cause of otitis externa (OE). Histological lesions of ceruminous gland hyperplasia and ectasia were observed in aural biopsies from 6/13 clinically healthy ears and 13/15 ears with OE from 19/28 examined dogs. Nine of 28 dogs had histologically normal ceruminous glands (odds ratio [OR] 6.2, 95% confidence interval [CI] 1.1-36.6). Bacterial growth in microbiological culture of aural exudate (OR 14.1, 95% CI 2.1-95.3) was associated with ceruminous glandular changes, whereas previous history of OE, cutaneous findings or underlying allergies were not. Pedigree analysis and a genome-wide association study (GWAS) were performed on 18 affected and eight unaffected dogs based on histopathological diagnosis. While the GWAS indicated a tentative, but not statistically significant, association of ceruminous gland hyperplasia and ectasia with chromosome 31, a larger cohort is needed to confirm this preliminary result. Based on our results, ceruminous gland hyperplasia and ectasia may also precede clinical signs of OE in ACSs and a genetic aetiological component is likely Further studies with larger cohorts are warranted to verify our preliminary results. (C) 2021 The Authors. Published by Elsevier Ltd.

Abstract Background American Cocker Spaniels are overrepresented among breeds that require surgery as a treatment of end-stage otitis externa. However, the prevalence of otitis externa (OE) in this breed remains unknown. We reviewed the year 2010 medical records of 55 private veterinary clinics in Finland to determine the prevalence of OE in American Cocker Spaniels compared with English Cocker and English and Welsh Springer Spaniels. An American Cocker Spaniel owner questionnaire was designed to identify potential risk factors for end-stage OE. Results From the medical records of 98,736 dogs, the prevalence of OE was highest in Welsh Springer Spaniels (149 out of 468, 31.8%, [95% confidence interval 27.6–36.0]), followed by American Cocker (89/329, 27.0%, [22.2–31.7]), English Springer (96/491, 19.6%, [16.1–23.1]) and English Cocker Spaniels (231/1467, 15.7%, [13.8–17.6]). The mean number of OE episodes in ear-diseased dogs and the number of ear surgeries were highest in American Cocker Spaniels. Owner questionnaires were received for 151 American Cocker Spaniels, 85 (56%) of which had suffered from OE. In 47% (40/85) of these dogs, OE occurred without concurrent skin lesions, 46% (33/72) displayed the first signs of OE before 1 year of age. In 24% (20/85) of the dogs, the signs of OE recurred within 1 month or continued despite treatment, 16% (14/85) required surgery (n = 11) or were euthanized (n = 5; 2 of the operated dogs and 3 others) due to severe OE. The onset of OE before the age of 1 year significantly increased the risk (OR 3.8, 95% CI 1.1–13.6) of end-stage OE. Conclusions The prevalence of OE in American Cocker Spaniels in Finland was higher than previously reported in Cocker Spaniels, but the highest prevalence of OE was found in Welsh Springer Spaniels. Compared to the other Spaniels, OE was more often recurrent and more frequently surgically managed in American Cocker Spaniels. Based on the questionnaire, early onset (<1 year) of OE increased the risk of end-stage OE. In American Cocker Spaniels, OE requires an intensive approach from the first treatment, and prevention of recurrence should be emphasised. The causes and treatment of OE in this breed warrant further study.