Brachycephalic obstructive airway syndrome (BOAS)

What is BOAS?

BOAS is a term used to describe the breathing problems dogs encounter associated with the extreme brachycephalic (shortened skull or flat faced) anatomy of many Pugs, English and French Bulldogs and Boston Terriers, as well as less commonly in Shih Tzus, Boxers and Persian cats.

Selective breeding of these breeds over the last 50 or so years has produced more and more extreme anatomy in some – the skull becomes shortened and rounded, the nose and muzzle become flattened into the face, the nostrils become narrow or pinched, the internal structures of the nose become deformed and the trachea (windpipe) is often much smaller in diameter than it should be.

These changes combine to produce much greater obstruction to the flow of air through the nostrils and nasal cavity and into the lungs, and back out again, meaning the dog’s respiratory system has to work much harder to get air in and out of the lungs than it should. This produces secondary changes to the soft tissues of the respiratory system so that with time they sag and swell, reducing the airway diameter and increasing the resistance to airflow even more.

Why is it a problem?

It is often considered ‘normal’ for dogs of these breeds to have noisy breathing and pant heavily but these are signs that the dog is straining to breathe and that the airway is not sufficient. Many of these dogs can live relatively normal lives but when they exercise or in hot weather their breathing can rapidly deteriorate. Some will struggle with even the most gentle of exercise or a mildly warm day.

As they get older the extra strain on their respiratory system over months and years can produce the secondary soft tissue changes described above so that their breathing gets worse with time. BOAS dogs are more prone to respiratory infections like pneumonia and because their respiratory system is compromised, they are more severely affected if they do develop an infection. It is not unheard of for BOAS dogs to die suddenly and without warning from acute respiratory obstruction.

Dogs with BOAS frequently also have gastrointestinal problems such as vomiting or regurgitation of food, and this is linked to the increased strain necessary to breathe.

What can be done about it?

For dogs who are already showing the signs of BOAS (panting frequently, struggling with exercise, heat intolerance, choking/retching frequently, collapsing) corrective surgery should be strongly considered. There are a number of procedures, usually performed at the same time, that can help increase the diameter of the respiratory system and reduce the resistance to airflow so that less force is necessary to breathe. Narrow nostrils can be widened, a soft palate that is too long can be shortened, and any extra soft tissue at the entrance to the trachea can be removed. These procedures often lead to a significant improvement in the dog’s breathing and ability to exercise and cope with warmer weather.

If you think your dog could benefit from this kind of surgery please contact us to discuss with a vet or book an appointment for assessment. We have performed this type of surgery on many dogs and our team is well trained in how to safely monitor and recover brachycephalic animals from BOAS surgery.

Breeding dogs with BOAS

The anatomical problems that lead to BOAS are a result of selective breeding and are inherited. As such, any dog showing signs of BOAS should not be considered for breeding. Neutering is possible at the same time as BOAS surgery, avoiding the need for a second general anaesthetic and meaning the dog only has to recover from surgery once.

If you are considering breeding from your brachycephalic dog, it is possible to assess their breathing formally prior to breeding. An exercise tolerance test is a simple and non-invasive way of comparing their breathing before and after a short but sustained period of exercise. If there is a major deterioration in breathing after the exercise, it is considered that the dog has some degree of BOAS.