Abstract
Extremely brachycephalic, or short-muzzled, dog breeds such as pugs, French bulldogs, and bulldogs are prone to the conformation-related respiratory disorder—brachycephalic obstructive airway syndrome (BOAS). Affected dogs present with a wide range of clinical signs from snoring and exercise intolerance, to life-threatening events such as syncope. In this study, conformational risk factors for BOAS that could potentially aid in breeding away from BOAS were sought. Six hundred and four pugs, French bulldogs, and bulldogs were included in the study. Soft tape measurements of the head and body were used and the inter-observer reproducibility was evaluated. Breed-specific models were developed to assess the associations between the conformational factors and BOAS status based on functional grading. The models were further validated by means of a BOAS index, which is an objective measurement of respiratory function using whole-body barometric plethysmography. The final models have good predictive power for discriminating BOAS (-) and BOAS (+) phenotypes indicated by the area under the curve values of >80% on the receiver operating curves. When other factors were controlled, stenotic nostrils were associated with BOAS in all three breeds; pugs and bulldogs with higher body condition scores (BCS) had a higher risk of developing BOAS. Among the standardized conformational measurements (i.e. craniofacial ratio (CFR), eye width ratio (EWR), skull index (SI), neck girth ratio (NGR), and neck length ratio (NLR)), for pugs EWR and SI, for French bulldogs NGR and NLR, and for bulldogs SI and NGR showed significant associations with BOAS status. However, the NGR in bulldogs was the only significant predictor that also had satisfactory inter-observer reproducibility. A NGR higher than 0.71 in male bulldogs was predictive of BOAS with approximately 70% sensitivity and specificity. In conclusion, stenotic nostrils, BCS, and NGR were found to be valid, easily applicable predictors for BOAS (+).
Highlights
Brachycephalic obstructive airway syndrome (BOAS) is a conformation-related respiratory disorder of dog breeds with shortened skulls and muzzles, such as the pug, the French bulldog, the bulldog, and others [1]
We found that approximately 50% of our study dogs in the three extreme brachycephalic breeds were BOAS-affected according to whole-body barometric plethysmography (WBBP), an objective respiratory function test [16]
Nostril stenosis is a strong predictor of BOAS for all three breeds
Summary
Brachycephalic obstructive airway syndrome (BOAS) is a conformation-related respiratory disorder of dog breeds with shortened skulls and muzzles, such as the pug, the French bulldog, the bulldog, and others [1]. Breeding selection for extreme brachycephalia has resulted in deformation of the upper airway tract leading to obstruction, as the soft tissues have not reduced proportionately with the length of the skull [2]. The average lifespan of brachycephalic breeds is reduced by approximately three years when compared to that of mesaticephalic and dolichocephalic breeds of similar body size [9,10,11,12], with much of this difference likely due to BOAS and its syndromic effects. The problems caused by BOAS have been compounded by the increased popularity of the three extreme brachycephalic breeds named above over the last two decades in the UK and elsewhere. All three breeds are amongst the top ten breeds in popularity in the UK [13]
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