LONDON, 13 MAY: A new study analysing the UK’s largest standardised dataset of respiratory function grades in Bulldogs, French Bulldogs and Pugs shows that differences in breathing function are influenced by genetics within these breeds.
The research, conducted by the Royal Kennel Club (RKC), demonstrates that meaningful improvements in respiratory health are achievable through informed breeding decisions, supported by the Respiratory Function Grading Scheme (RFGS), marking an important step forward in improving the welfare of brachycephalic dogs. The paper, led by The Royal Kennel Club’s Geneticist Dr Joanna Ilska, has been published in the peer-reviewed journal PLOS One, highlighting the organisation’s growing contribution to high-impact scientific research
The brachycephalic (flat-faced) head shape of these breeds is commonly linked to Brachycephalic Obstructive Airway Syndrome (BOAS), a respiratory condition that impairs normal breathing; however, not all dogs within these breeds are affected. To help guide breeding decisions with scientific evidence, the Royal Kennel Club and the University of Cambridge launched the Respiratory Function Grading Scheme in 2019. The scheme uses a standardised examination and exercise test to assess breathing in individual dogs, particularly those being considered for breeding, while also generating valuable population-wide data.
For the recently published paper, RKC researchers analysed over 4,000 RFGS assessments across Bulldogs, French Bulldogs and Pugs, alongside pedigree records, to better understand the genetic basis of respiratory function and evaluate participation in health screening across the RKC registered, UK population of these breeds.
The study found that the prevalence of Brachycephalic Obstructive Airway Syndrome (BOAS) in the largest sample studied to date across the three breeds was between 16 and 20 percent. Importantly, the results showed moderate heritability of respiratory function (between 22 and 45 percent), indicating that selective breeding can lead to measurable reductions in the prevalence of the condition.
As a result of these updated prevalence figures and the continued evolution of evidence from the scheme, the Royal Kennel Club is updating its breeding advice within the Respiratory Function Grading Scheme. From 13 May, all mating pairings involving a Grade 2 dog will be designated as “red” (not recommended), reflecting the updated evidence and increased confidence in the scheme’s guidance for breeding decisions. The research also identified that nostril stenosis, a narrowing of the nostrils, is heritable and genetically linked to respiratory function, although it is a distinct trait. In addition, the study highlighted that dogs bred outside of breed standards, such as those with non-standard colours, are less frequently presented for testing, despite making up a significant proportion of the population. Overall participation in the scheme remains relatively low, suggesting further engagement is needed to maximise its impact.
Dr Joanna Ilska, Geneticist and lead author of the paper, said: “Our findings provide clear evidence that respiratory health in these breeds is influenced by genetic differences between dogs, and importantly, that improvement is achievable through selective breeding. By using objective tools like the Respiratory Function Grading Scheme, breeders can make more informed decisions that prioritise health, helping to reduce the prevalence of BOAS over time.
“It is also important to recognise that this research is based on dogs within the Royal Kennel Club’s registered population and may not reflect those bred outside of this system. This highlights the value of Royal Kennel Club registration, as participation in schemes like the RFGS allows registered dogs to contribute to scientific research that supports the long-term health and welfare of the breed.
“Increasing participation in health screening is also key to achieving progress and ensuring that future generations of these popular breeds can enjoy better quality of life.”
The analysis also found that age at testing had a statistically significant but very small effect on RFGS grades, consistent with previous studies showing minimal or no influence of age. In combination with the high repeatability of results, these findings have informed an update to the scheme’s protocol. Therefore, from 1st June, the Royal Kennel Club will update the RFGS protocol so that repeat assessments beyond six years of age are no longer required, with assessments carried out at or after this age issued without an expiry date. Dogs are still recommended to be first tested from 12 months of age, with results valid for 24 months up to six years of age. Historic results will be automatically updated to reflect this change on Health Test Result Finder.
The research findings have informed updates to the scheme and support the continued development of breeding strategies focused on functional health, alongside increased uptake of screening, to help reduce respiratory issues and improve overall welfare in brachycephalic breeds.
As participation in the scheme continues to expand, it will be regularly reviewed and refined to ensure it reflects the latest scientific evidence and remains a robust and consistent tool for supporting breeding decisions.
The full study, titled ‘Quantitative genetic analysis of respiratory function and related traits in Bulldogs, French Bulldogs and Pugs’, is available via PLOS One.
The Royal Kennel Club’s Health team will also be holding a webinar on 20 May at 7pm to share the paper’s findings and discuss what they mean for breeders and owners. Further details on how to register can be found here.