BOAS in the Boston Terrier: A healthier screw-tailed breed?

Abstract

Brachycephalic obstructive airway syndrome (BOAS) is well documented in the three most popular brachycephalic dog breeds of the UK and several other countries: French Bulldogs, Pugs and Bulldogs. More extreme conformation has been found to be associated with increased risk of BOAS and other brachycephalic disease in these breeds, such as ocular, neurological, and dental disease. Less is known about how BOAS and other brachycephalic conformation-related disease affects other breeds such as the Boston Terrier. In this study, one-hundred and seven Boston Terriers were prospectively recruited from the UK dog population and underwent clinical assessment, respiratory function grading and conformational measurements. Whole-body barometric plethysmography was used in a smaller cohort of dogs to compare the quantitative differences in respiratory parameters between both affected and unaffected Boston Terriers, and control mesocephalic dogs. When compared to an equivalent study population of French Bulldogs and Bulldogs, it was found that Boston Terriers have a significantly higher proportion of BOAS Grade 0 dogs at 37.5% compared to 10% and 15.2% respectively (p<0.01). Within the breed, more extreme brachycephalic conformation was found to be associated with an increased risk of BOAS: specifically, nostril stenosis, facial foreshortening, abnormal scleral show, and higher neck to chest girth ratio. However, there is considerable overlap between measurements of affected and unaffected dogs in these variables. Therefore, the use of respiratory function grading is likely to be more advantageous for owners, breeders, and veterinary surgeons in accurately selecting unaffected dogs.

Fig 1. Soft tape body measurements.

Line colours corresponding to the following measurements: (a) Blue: body length, (b) Orange: body height, (c) Pink: neck girth, (d) Yellow: chest girth, (e) Green: tail length.

Fig 2. Photographic conformational measurements.

(A) Frontal plane (FP) photographs were taken with the camera facing directly from rostral to caudal, with the subject looking directly at the camera lens. Measurements include ICD (pink line) and SW (green line). (B) Dorsal plane (DP) photographs were taken with the camera looking down at the subject from a bird’s eye view; dorsally to ventrally and perpendicular to the frontal plane. Measurements include SW (green line) and SL (yellow). (C) Sagittal plane (SP) photographs were taken as a side-on view, directly lateral to the subject and parallel to the midline sagittal plane. Measurements include MzL (red line) and CrL (blue line).

Fig 3. The BOAS grade distribution of Boston Terriers in the sample population.

Percentages compared to that of graded of Bulldogs and French Bulldogs in the previous study by Liu et al. [1].

Fig 4. Mean mid-expiratory flow rates recorded at each quartile of the expiratory breath.

Considered for three sample populations: 1. Control dogs, 2. BOAS Grade 0 Boston Terriers (BTs) and 3. BOAS Grade 1–3 Boston Terriers (BTs). Flow rates have been normalised to body weight (kg). Error bars displayed and 95% confidence intervals represented by dashed lines.

Fig 5. Example whole-body barometric respiratory flow traces from the three sample populations.

(A) Control dog. (B) Grade 0 Boston Terrier. (C) Grade 2 Boston Terrier.

Fig 6. Boxplots of conformational measurements in Grade 0 versus Grade 1–3 Boston Terriers.

Neck to chest girth ratio (p = 0.039), tail length (p = 0.052), skull index (p = 0.0002) and craniofacial ratio (p<0.0001).

Fig 7. The percentage of BOAS Grade 0 versus BOAS Grade 1–3 Boston Terriers across different subjective conformation variables.

Nostril stenosis (p = 0.002), scleral show (p = 0.04) and body condition score (p = 0.15).

Fig 8. Multiple logistic regression analysis of selected signalment and conformational factors.

Six variables included in analysis (nostril stenosis, scleral show, NGR, tail length, SI and CFR) with classification cut-off value at 0.5. Boxplot displaying the probability of the model predicting observed BOAS Grade 0 (0) and BOAS Grade 1–3 (1). Receiver operating characteristic (ROC) curve of the model with area under curve of 0.868 (Std. error: 0.0411, 95% CI: 0.788–0.949, p<0.0001).

Fig 9. Comparative illustration of the conformation of Boston Terriers with lower and higher BOAS risk.

(A) Lower risk conformation characteristics: longer muzzle with narrower skull, no abnormal scleral show, open nostrils, and proportionally slimmer neck. (B) Higher risk conformation characteristics: more extreme facial hypoplasia with shortened muzzle and wider skull, abnormal scleral show, stenotic nostrils, and proportionally thicker neck.