The mobility of the brachycephalic canine nostril in relation to the degree of nostril stenosis.

Previous studies have shown that the most reliable external conformational risk factor of whether a brachycephalic dog will develop Brachycephalic Obstructive Airway Syndrome (BOAS) is the status of nostril stenosis, assessed as a static observation using the brachycephalic nostril grading scheme. The nostrils however are a dynamic structure, opening further when the dog is exercising, sniffing or panting. The hypothesis of this study was that brachycephalic dogs with open or mildly stenotic nostrils are more likely to have nostril mobility whilst dogs with moderately or severely stenotic nostrils are more likely to have immobile nostrils. A retrospective study of dogs presented for BOAS assessment at two UK referral centres between 2012 and 2020 was performed. Data extracted included nares stenosis status and nares mobility. A mesocephalic pilot control group was recruited from a third referral centre. Statistical analysis was performed with χ2, Cochran-Armitage, spearman's rho and linear-by-linear tests as appropriate. Of the 974 brachycephalic dogs included in the study: 124 had open nostrils (68.5% mobile); 212 mildly stenotic nostrils (58.5% mobile); 379 moderately stenotic nostrils (35% mobile) and 259 severely stenotic nostrils (19.3% mobile). The nostril stenotic status was significantly associated with nostril wing mobility (χ2 =135.55; P<0.0001). When considering open and mildly stenotic (considered acceptable) nostrils versus moderate and severely stenotic nostrils, mobility was 62% versus 25.5% (χ2= 135.88; P = <0.0001). All 27 mesocephalic dogs had nostril mobility. Brachycephalic dogs with moderate and severely stenotic nares have reduced nasal mobility compared to brachycephalic dogs with mildly stenotic and open nares. Data is further evidence that dogs with moderately and severely stenotic nares should not be bred.