Understanding how BOAS and nostril grades for brachycephalic dogs are scored

BOAS or brachycephalic obstructive airway syndrome is a health condition that can occur in dogs with brachycephalic faces that have a high degree of exaggeration to the flatness of their muzzles. The shorter the dog’s muzzle is, the more likely they are to have conformation defects that will in their turn negatively impact on the dog’s ability to breathe normally, which compromises their quality of life and potentially, lifespan too.

Brachycephalic dog breeds like the Pug, French bulldog and English bulldog are really popular in the UK – and all three of these breeds are ranked in the top 10 list of the UK’s most popular dog breeds overall. However, these same three breeds are also three of those most likely to be bred for a highly exaggerated flat face – which can lead to BOAS and other problems.

Dogs that do suffer from BOAS will need careful management and care to ensure that the impact of the condition is minimised, and that the dog can maintain a reasonable quality of life – and dogs who suffer from acute BOAS may require a complex and challenging surgery to help to ease the issue.

All brachycephalic dogs should be examined by a vet to identify how they rank for BOAS, and if the initial examination is performed when the dog is young, it should be repeated when they reach the age of two years old as well.

The Department of Veterinary Medicine at the University of Cambridge has drawn up a grading system for brachycephalic dogs, to provide some uniformity across veterinary professionals when it comes to assessing dogs and interpreting examination results.

If you have your dog examined for BOAS, they will probably be given both a BOAS grade (known as a functional BOAS grade) and also a nostril grade too, which reflects the conformation and impact (or otherwise) that BOAS has upon the dog in question.

Knowing what your dog’s functional BOAS grade and nostril grade means is important in order to allow you to interpret these results – and decide, alongside of your vet, if your dog needs any special care or may require corrective surgery.

In this article we will explain how BOAS and nostril grades for brachycephalic dogs are determined, so that you can understand what your own dog’s results mean. Read on to learn more.

Functional BOAS grading

When examined for BOAS, dogs are assessed both at rest, and after exercise as the dog will breathe more heavily and so, display more acute symptoms after they’ve been working hard. This part of the test is called the exercise tolerance test.

BOAS is graded according to four rankings, which are grades 0-3, with 0 being the most desirable and healthy result and 3 being the most acute and serious.

Here is how BOAS grades are determined.

BOAS grade 0

• Respiratory noise (or audible respiration) is not present or cannot be heard from the dog either at rest or after exercise.
• The dog doesn’t have to make any inspiratory effort (this means struggling or working harder to inhale) either at rest or after the exercise tolerance test.
• No dyspnoea, syncope or cyanosis are present either before or after exercise. Dyspnoea means laboured breathing, syncope means temporary, short-term loss of consciousness, and cyanosis means bluing of the mucous membranes that can occur if there’s not enough oxygen in the bloodstream.

BOAS grade 1

• Respiratory noise is either not audible or mild when at rest, and mild after the exercise tolerance test.
• There’s no inspiratory effort at rest, and no or mild inspiratory effort after exercise.
• No dyspnoea, syncope or cyanosis are present either at rest or after exercise.

BOAS grade 2

• At rest, respiratory noise is mild to moderate and after exercise, moderate to severe.
• Inspiratory effort at rest is mild to moderate, and after exercise, moderate to severe.
• Dyspnoea, syncope and cyanosis are not present at rest, and after exercise, dyspnoea is mild but neither syncope nor cyanosis are present.

BOAS grade 3

• Respiratory noise is moderate to severe even at rest, and is severe after the exercise tolerance test.
• Inspiratory effort is moderate to severe at rest, and severe after exercise.
• Moderate or severe dyspnoea is present at rest, and cyanosis may be present. The dog is unable to tolerate normal exercise safely.
• Post-exercise, the dog suffers from severe dyspnoea and may or may not suffer from syncope and cyanosis too.

Nostril grades for brachycephalic dogs

Alongside of BOAS grade scoring, brachycephalic dogs will also usually have their nostrils assessed too. Brachycephalic dog may have very narrow nostrils as a result of conformation exaggerations, which contributes to BOAS and also, serves as a standalone problem that can impact the dog’s ability to get enough air.

Nostril grades assess how wide or narrow the nostrils are compared to healthy norms, and are scored from 1-4, with 1 being the best possible result and 4 the worst.

Here’s what the four grades mean.

Nostril grade 1

The dog’s nostrils are considered to be as open as is possible/desirable for the dog’s breed, classed as wide open and healthy.

Nostril grade 2

The dog’s nostrils exhibit signs of mild stenosis (narrowing), but this should not be a problem as long as this trait doesn’t cause any problems for the dog themselves.

When the dog is exercising or working hard, the nostrils should be able to open naturally to enable normal respiration.

Nostril grade 3

Moderate stenosis (narrowing) of the nostrils is present, but considered to be passable unless the dog also shows signs that this is compromising their respiration or causing them to breathe through their mouths.

The nostrils themselves are only open at the bottom, and don’t flare and contract when the dog is exercising.

Nostril grade 4

Dogs with nostril grade 4 have nostrils that are almost entirely closed, which may lead to them mouth-breathing after only gentle exercise or even at rest. This is the most severe and acute nostril grade a dog can receive.

Why is this information useful?

Knowing how your dog measures up when it comes to BOAS and nostril scores is helpful for a variety of reasons. First of all, it tells you more about your dog’s health and any specific challenges, which you may need to accommodate for and manage in order to keep them well.

Additionally, it can allow you to determine if your dog’ conformation is having a significant negative impact on their quality of life and general wellness, which may necessitate corrective surgery to try to ease the issue.

It is also valuable and essential information for responsible dog breeders, so that they can make an informed decision about breeding from only healthy dogs that won’t pass on conformation defects that can affect the health of their own offspring too.