Brachycephalic obstruction airway syndrome (BOAS)

Over the past hundred years human beings have designed for themselves a huge number of different dog breeds. The conformation of some of these breeds has become more extreme and sadly many health problems have been introduced into the dog population as a consequence. The continual increased selection pressure for ‘desirable’ physical traits has resulted in many pets presenting with more severe manifestations of certain congenital conditions and at a much younger age. If you are considering buying, or already own, a dog with a flat face such as a Pug, Boston terrier, Pekingese or Bulldog then you need to be aware of the welfare issues surrounding brachycephalic obstruction airway syndrome.

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Brachycephalic obstructive airway syndrome otherwise known as BOAS arises from the effects of a group of congenital anatomical defects present in brachycephalic breeds. Brachycephalic breeds of dogs are those with characteristically flat faces such as the bulldog, Boston terrier, French bulldog, Pug, and Pekingese. Animals with flat faces still have the same amount of tissue in their nose and throat but this is squashed into a smaller space which causes folds and wrinkles that obstruct the airways. Animals with BOAS may have one or more of the following defects:

• Stenotic nostrils
• Obstructed nasal cavity
• Excessively long and thickened soft palate
• Narrowed laryngeal lumen
• Nasopharyngeal collapse
• Excessively narrow trachea, especially common in bulldogs.

The abnormal anatomical conformation of these dogs means that airflow through airways is impeded resulting in noisy breathing and an inability to take on board sufficient oxygen to meet increased demands imposed by exercise. The nasal cavity has a huge surface area covered by richly vascularized tissue that in normal dogs cools inhaled air thus forming an important part of the body’s mechanism for temperature regulation. This is compromised in brachycephalic breeds, and many breathe through their mouth bypassing the nasal cavity altogether. This explains why many of these breeds have poor heat tolerance and cope poorly with hot weather. The nasal obstruction also contributes to sleep disorders and regurgitation of food and froth. Hot weather also causes swelling of the tissues in the nose and throat further impeding airflow and exaggerating symptoms.

Severely affected dogs may show signs of breathing problems at a very young age (4-6 months of age) although most will present with signs at around 1-3 years of age. The first signs you may notice if your dog has BOAS are that it has noisy breathing or may snore loudly whilst sleeping. In fact many owners of dogs with short noses such as pugs and bulldogs think it is normal for their pets to snore and snuffle. However, these noises indicate that their pet’s airways are already narrowed and breathing is difficult. Dogs with BOAS frequently have significantly disrupted sleep as every time they lie down and relax their airways become obstructed.

Many French bulldogs with BOAS will have gastrointestinal signs, particularly regurgitation or food or fluid particularly when exercised or excited. This can be seen in the other breeds too and sometimes bulldogs will produce pools of saliva when exercising if the palate is too large as they struggle to breathe and exercise. Always make sure you give your veterinarian a full history of all your dog’s problems even if you think one (like breathing difficulties) is more important. In many cases treatment of the airway problem with improve the gastrointestinal symptoms but more severely affected patients may require additional medication.

Many dogs with BOAS are unwilling (or unable) to exercise normally and this can predispose them to putting on weight which further exacerbates their problems. Sudden deterioration in breathing may develop, leading to respiratory distress or sudden collapse (particularly in hot weather). This deterioration may be brought on by exercise and excitement. Severely affected animals may have almost total airway obstruction and can develop fluid build-up on the lungs. Animals that have severe bouts can die rapidly if they do not get emergency veterinary treatment.

The diagnosis is based on the clinical signs (and typical breed), but further examination may be required to confirm the diagnosis and rule out other conditions. If your veterinarian suspects that your dog is suffering from BOAS they will want to perform a thorough clinical examination including an exercise test to assess breathing function. A detailed inspection of the upper airway with your dog under anesthesia may be indicated if they have diagnosed BOAS and they may pass an endoscope (containing a small camera) through your dog’s airways so they can access which abnormalities your dog has and how severe each of these is. These examinations are best performed by a veterinary surgeon experienced at treating this condition so that treatment can be carried out at the same time. Anesthesia and examination without correction poses unnecessary risk to your pet.

Most overweight animals with BOAS will be improved if they lose weight so a dietary regime forms part of any management. Because BOAS is caused by congenital abnormalities of the airways the only way to improve the problems is to correct the underlying abnormalities. Surgical procedures can open up the nostrils and remove some of the excess tissue within the airways that is restricting airflow. Surgical correction requires a great deal of skill and is not without risks. Your veterinarian may choose to refer you for treatment to a surgeon who specializes in these procedures. Following surgery the lives of affected animals should be significantly improved. Correction of the reversible primary abnormalities early in life will slow down or potentially prevent secondary irreversible changes occurring that would otherwise compromise the airway further. This emphasizes the importance of critically evaluating how well you pet can breathe early in life and seeking professional advice.

Since the condition is inherited it is important not to breed from animals that suffer from BOAS (even if they have had surgery) as their offspring will also be affected. Unfortunately most show animals in affected breeds have been deliberately bred to produce the external appearances that are the result of these defects (such as a very short nose and flat face) so the defects are present to a greater or lesser extent in all animals within the breed. Ultimately BOAS is a significant welfare issue in brachycephalic breeds and the only way this can be alleviated is by breeder acceptance that extreme conformations (such as excessively flat faces) are not desirable in dogs.

The Kennel Club/ University of Cambridge Respiratory Function Grading (RFG) Scheme was launched in 2019 to help breeders decide which dogs are suitable for breeding. Any dogs showing severe BOAS should not be bred and breeders are now producing some grade 0 and grade 1 dogs. It is important that owners considering purchasing a brachycephalic puppy looks for one in which the parents are both health tested, including the RFG Scheme. All Assured Breeders from the Kennel Club Scheme will have health tested dogs.

If your dog is registered with the Kennel Club and has had correction of any conformation abnormalities associated with BOAS please notify the Kennel Club that these surgical procedures have been performed.

If you are worried about your pet in any way, but especially if it appears to have breathing problems, then you should contact your veterinarian for advice.