Understanding BOAS and Nostril Grades in UK Brachycephalic Dogs

Brachycephalic obstructive airway syndrome (BOAS) is a significant health condition affecting brachycephalic dog breeds with shortened muzzles. This condition results from extreme flatness of the face, causing breathing difficulties that can lower a dog's quality of life and lifespan. Popular UK breeds like the Pug puppies, French Bulldog puppies, and English Bulldog puppies are especially prone to BOAS due to selective breeding favouring exaggerated flat faces.

BOAS is assessed using a standardized grading system developed by the Department of Veterinary Medicine at the University of Cambridge, aiming to provide uniformity across veterinary professionals in evaluating dogs. Dogs are given two assessments: a functional BOAS grade and a nostril grade, which together help owners and vets understand the severity of airway obstruction and guide management and breeding decisions.

Functional BOAS Grading Explained

The functional BOAS grading involves observing a dog's respiratory function at rest and after an exercise tolerance test, as symptoms often worsen with exertion. The grades range from 0 to 3, with 0 indicating no signs of BOAS and 3 reflecting severe disease.

BOAS Grade 0

• No respiratory noise at rest or after exercise.
• No inspiratory effort or laboured breathing.
• No signs of distress such as dyspnoea, syncope, or cyanosis at any time.

BOAS Grade 1

• Respiratory noise mild or absent at rest, mild after exercise.
• No or mild inspiratory effort post-exercise.
• No cyanosis or syncope.

BOAS Grade 2

• Mild to moderate respiratory noise at rest, moderate to severe after exercise.
• Mild to moderate inspiratory effort at rest and more severe after exercise.
• Mild dyspnoea post-exercise without syncope or cyanosis.

BOAS Grade 3

• Moderate to severe respiratory noise at rest, severe after exercise.
• Moderate to severe inspiratory effort worsening with activity.
• Moderate or severe distress signs like cyanosis, syncope; normal exercise unsafe.

Nostril Grading for Brachycephalic Dogs

Nostril assessment grades from 1 to 4 reflect how open or narrowed a dog's nostrils are, which directly influences breathing comfort. Narrowed nostrils increase airflow resistance, contributing to BOAS severity.

Nostril Grade 1

Nostrils are wide open and as healthy as possible for the breed.

Nostril Grade 2

Mild narrowing exists, but nostrils can open with exercise without breathing issues.

Nostril Grade 3

Moderate narrowing restricts airflow; nostrils are only open at the bottom and do not flare during exercise. Dogs may breathe through their mouths.

Nostril Grade 4

Severe stenosis causes almost complete nostril closure, leading to mouth breathing at rest or after mild activity.

Why These Grades Matter

Understanding your dog's BOAS and nostril grades is critical to managing their health and wellbeing responsibly. It allows owners and veterinarians to determine if the dog requires special care, lifestyle adjustments, or possibly corrective surgery to improve airflow. For breeders, these grades provide essential guidelines to avoid breeding dogs with severe airway obstruction, thereby improving future generations' health and welfare.

Leading veterinary and welfare experts endorse strict use of these grading systems to promote responsible ownership and breeding. Since 2025, major dog events like Crufts require participating Pugs, Bulldogs, and French Bulldogs to have a valid respiratory function grading, reinforcing health prioritisation over appearance.

For owners considering getting a brachycephalic dog, it's advisable to research health screening and choose reputable breeders who prioritise the dog's respiratory health rather than exaggerated aesthetics. This helps ensure a dog with fewer breathing problems and a better quality of life.

Responsible ownership includes regular vet checks from young age, monitoring breathing, avoiding overexertion or heat stress, and being alert to any signs of distress. If your dog is affected by BOAS, collaborate closely with your vet for tailored management and advice.

This article provided you with a clear understanding of how BOAS and nostril grades are scored, giving you the knowledge needed to care for your brachycephalic dog more effectively and support responsible breeding practices that improve canine welfare over time.