Study links genes to breathing in 4,000+ flat-faced dogs

Joanna Jadwiga Ilska and colleagues published a PLOS One study on May 13 that tied breathing function and nostril narrowing in Bulldogs, French Bulldogs and Pugs to inherited traits. The paper analyzed more than 4,000 dogs using respiratory grading records and pedigree data collected through the Royal Kennel Club’s screening program. The authors said the results support selective breeding within those breeds to reduce brachycephalic obstructive airway syndrome, or BOAS, a disorder linked to the shortened skull shape seen in flat-faced dogs. The Royal Kennel Club said the findings were strong enough that it updated breeding guidance the same day. ### Which dogs were included in the research? The study examined Bulldogs, French Bulldogs and Pugs, three breeds commonly described by veterinarians as brachycephalic because of their shortened muzzles. The researchers used data from the Respiratory Function Grading Scheme, a standardized exam and exercise test launched in 2019 by the Royal Kennel Club and the University of Cambridge for dogs being considered for breeding. (journals.plos.org) More than 4,000 dogs were included alongside pedigree records, making the sample several times larger than earlier reference datasets cited in the public release. The paper said the goal was to estimate heritability of respiratory function and assess how widely owners of registered dogs were participating in screening. ### What did the researchers find about genetics and breathing? (journals.plos.org) The PLOS One paper reported moderate heritability estimates for respiratory function grades of 0.21 to 0.49 and for nostril stenosis of 0.31 to 0.39. In the public release, the researchers translated that to roughly 21% to 49% of the variability in respiratory function and 31% to 39% of the variability in nostril size being attributable to genetics. (journals.plos.org) The authors also found significant genetic correlations between respiratory scores and nostril narrowing. The Royal Kennel Club said the results indicate that breeding decisions can produce measurable improvements in respiratory health within the three breeds, rather than treating breathing problems as an unavoidable feature of flat-faced dogs. ### How common was the breathing disorder in the screened dogs? (journals.plos.org) French Bulldogs had the lowest BOAS prevalence in the tested sample at 15.6%, compared with 18.9% in Bulldogs and 19.8% in Pugs, according to the EurekAlert release summarizing the study. The Royal Kennel Club separately described the prevalence in the largest sample studied to date as between 16% and 20% across the three breeds. (journals.plos.org) The authors said those rates were lower than previous estimates. In the public materials, they said one possible reason is that many flat-faced dogs are not screened unless they already show symptoms, while the larger dataset may also reflect more recent health-management changes. ### What traits tended to appear together? Poor respiratory function, narrow nostrils and higher body weight tended to co-occur in the analysis, the researchers said. (eurekalert.org) The release said that pattern suggests breeders may be able to improve respiratory health by avoiding dogs with those traits in mating decisions, while owners of existing dogs can reduce strain by keeping them lean, allowing frequent breaks on walks and helping them stay cool. The paper itself described nostril stenosis as genetically linked to respiratory function but still a distinct trait. That matters because the researchers were not only measuring whether a dog struggled to breathe after exercise, but also whether visible features associated with airway restriction were being passed on. ### What changed after the study came out? (eurekalert.org) On May 13, the Royal Kennel Club said it updated breeding advice under the Respiratory Function Grading Scheme. The group said all mating pairings involving a Grade 2 dog would now be designated “red,” meaning not recommended, based on the updated evidence from the new analysis. (journals.plos.org) The PLOS One article said wider participation in respiratory screening will be needed if breeding programs are to reduce BOAS prevalence across these breeds. The next step is not a new treatment but broader use of testing data by breeders and breed organizations already working within the grading scheme. (journals.plos.org) (royalkennelclub.com)