Conformational risk factors of brachycephalic obstructive airway syndrome (BOAS) in pugs, French bulldogs, and bulldogs

PLoS One. 2017 Aug 1;12(8):e0181928. doi: 10.1371/journal.pone.0181928. eCollection 2017.


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 (+).

MeSH terms

  • Airway Obstruction / diagnosis
  • Airway Obstruction / genetics
  • Airway Obstruction / veterinary*
  • Animals
  • Breeding
  • Craniosynostoses / diagnosis
  • Craniosynostoses / genetics
  • Craniosynostoses / veterinary*
  • Dog Diseases / diagnosis*
  • Dog Diseases / genetics
  • Dogs
  • Female
  • Male
  • Observer Variation
  • Plethysmography, Whole Body
  • Regression Analysis
  • Reproducibility of Results
  • Risk Factors
  • Species Specificity
  • Syndrome

Grants and funding

The Kennel Club Charitable Trust (RG71960, provided financial support and sources for data collection to DRS, LK. NCL, and JFL. Cambridge Overseas Trust ( supported NCL for her PhD. The current study was conducted during her PhD but was not included in her thesis. VJA runs her own commercial consultancy company, Vet Epi. VJA was involved in data acquisition and manuscript preparation and was remunerated for her work on the project from the research grants. Vet Epi did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.