BOAS in dogs

Overview

Narrowed upper airways

BOAS can start young and affect breathing throughout life. Several sites between nostrils and larynx can be narrowed simultaneously. Resting breathing can appear normal despite exercise revealing signs.

One breeding test programme from northern Europe followed 957 dogs during 2017–2022. Moderate or severe respiratory signs affected 28% of tested Bulldogs. French Bulldogs had 22%. Pugs had 30%.

Respiratory grades were available for 810 tested dogs. Eleven per cent of Bulldogs failed the exercise section, though more had moderate or severe signs.

Causes

Muzzle and throat structure

Short skulls leave less soft tissue space because tissues do not always shrink proportionately with bone. Narrow nostrils restrict entry into the nasal cavity. Turbinates can obstruct the nasopharynx when nasal space is limited. An elongated soft palate can extend over the airway entrance and impede flow to the lungs. Some dogs also have a narrower trachea.

Nostrils can collapse inwards during breathing, further reducing space. Narrowing can also lie behind the opening in the nasal vestibule. A thick tongue base can impair breathing, particularly during closed-mouth sleep. A thickened soft palate can vibrate during inhalation, causing low-pitched noise.

Breathing effort and cooling

Narrowing increases resistance and the effort needed to inhale. Strong inhalation generates negative pressure, drawing soft tissue into the airway. Tissue in front of the vocal folds can evert as small laryngeal saccules, occupying airway space.

Panting cools through evaporation from the tongue and respiratory lining. Short muzzles have less nasal cooling surface. Heavy panting can irritate narrow airways and worsen swelling.

Risk factors

Risk increases as muzzle length decreases relative to skull length. Its importance varies within breeds because nostrils and body condition also affect breathing. Pekingese and Japanese Chins had high risk in a 14-breed comparison. Moderate or severe nostril narrowing affected 71% of assessed Pugs in the northern European breeding programme. Large neck circumference was associated with greater risk in two populations.

A combined Bulldog, French Bulldog and Pug comparison found an odds ratio of 3.8 for clinical BOAS in obese dogs versus others. Narrow nostrils had an odds ratio of 2.6.

The northern European programme found moderate or severe narrowing in 55% of French Bulldogs with assessed nostrils. Bulldogs had 40%.

Typical symptoms

Noise may initially occur only with excitement, activity or eating. High-pitched inhalation can indicate laryngeal narrowing.

• Noisy breathing or snoring during sleep.
• Mouth breathing with light exercise.
• Tiring quickly during play or walks.
• Gagging during swallowing.
• Regurgitation without vomiting effort.
• Brief interruptions to breathing during sleep.

Some prefer sleeping on their backs, moving the soft palate away from the laryngeal opening. One home-monitoring study from northern Europe found median obstructive sleep breathing indices of 3.8 in brachycephalic dogs and 0.7 in normal-muzzled dogs.

Dogs may visibly flare nostrils to draw in air. Affected dogs may sleep sitting up. The monitoring index describes obstructive pauses and partial breathing disturbances relative to recording time.

Complications and consequences

Larynx, heat and reflux

Persistent negative pressure can weaken laryngeal cartilage rigidity. Inward collapse can become permanent and further narrow the airway. Severe difficulty can cause oxygen deprivation and fainting.

A UK study found a heat-related illness odds ratio of 2.10 in brachycephalic versus medium-muzzled dogs. Food or gastric reflux can irritate the oesophageal lining. Inhaled regurgitated material can cause aspiration pneumonia.

Severe airway-related heatstroke can impair other organs. Sleep obstruction can reduce quality of life. Laryngeal damage can impair breathing despite surgical relief of original narrowing.

Diagnosis at the vet

Examining breathing

The vet assesses inhalation effort. Nostril shape and opening show narrowing. Throat and larynx can be examined endoscopically under sedation or anaesthesia. A thick tongue can block the view in awake dogs. Chest X-rays can identify a narrow trachea. Head CT can help plan nasal or soft palate surgery.

Formal testing and respiratory grades

One formal breeding test scheme requires a minimum age of 18 months. Dogs with breathing difficulty need clinical assessment and cannot undertake its exercise section. Most breeds walk 1,000 metres within 12 minutes. Pugs, French Bulldogs and Boston Terriers have an 11-minute limit. Pekingese cover 800 metres. Recovery is monitored for 15 minutes. Afterwards, the vet assesses general condition, heart rate and temperature.

Grade zero means no observed signs. Grade one means mild signs. Grade two means moderate signs. Grade three means severe signs. In the northern European programme, 94% passed the exercise section. Passing did not exclude moderate or severe respiratory signs.

This scheme's initial examination also checks mucous membrane colour and general condition. Ambient temperature must be 15–25 °C. Initial body temperature above 39.3 °C precludes passing the exercise section. Temperature above 39.5 °C during testing also means failure. Results obtained from age two remain valid indefinitely unless replaced by a new result. Airway surgery excludes participation in the breeding test. UK functional grading often uses a three-minute trot test. Breathing sounds can be assessed before and after that short exercise.

Treatment

Acute breathing difficulty

A severe crisis first requires adequate oxygenation. Supplemental oxygen can help when narrowing compromises supply. Severe obstruction may require a temporary tracheostomy. Cooling starts immediately in overheated dogs.

Surgery on obstructing structures

Weight reduction can help mild disease in overweight dogs. Symptoms and anatomy guide surgical decisions. Nostrils can be widened to improve nasal airflow. Elongated soft palates can be shortened. Thickened palates can also be thinned. Everted saccules can be removed during the same procedure when needed.

Breathing is monitored closely afterwards because swelling can obstruct the airway. Hospital monitoring usually lasts at least 24 hours. Coughing or gagging can occur. Bleeding as well as inflammatory swelling can obstruct recovery-phase breathing. One 80-dog follow-up found complications in 25, or 31.25%. Complications were more common with greater laryngeal collapse. Severe permanent laryngeal narrowing may sometimes require permanent tracheostomy.

Breathing after surgery

A 32-dog long-term follow-up found improved respiratory function versus before surgery. Median assessment time was 1,645 days afterwards. Eight dogs, or 25%, retained grade-two signs. Six, or 19%, had no detectable signs during testing. Thirty-three dogs receiving a second airway operation were excluded from this long-term assessment.

Prevention

Breeding can favour longer muzzles relative to breed average. Assessment considers breathing sounds and sufficiently open nostrils. Heritability estimates for BOAS grade in the northern European programme were 0.39–0.58. Breeding selection can therefore aim to reduce offspring symptoms.

Some countries' welfare rules restrict breeding likely to cause substantial harm to parents or offspring. Extremely short muzzles causing persistent breathing difficulty exemplify harmful conformation. Those welfare requirements cover purebred and crossbred dogs.

One northern European registry found at least one BOAS-tested parent in 89–100% of Bulldog, French Bulldog and Pug litters registered in 2022, depending on breed. Breeding assessment considers exercise tolerance, symptom grade and nostril narrowing together.

Important for dog owners

Use a harness to avoid lead pressure on the airway through the neck. In hot weather, keep walks short and choose the coolest times. Stop exercise immediately with overheating. Move to a cooler place and run cool water over the body. Keep cooling water away from the face.

Start cooling before transport for suspected heatstroke. Weight management can ease daily breathing in mildly affected overweight dogs.

Frequently asked questions

Is snoring normal in flat-faced dogs?

Snoring and low-pitched noise can reflect airflow through narrowed upper airways. Noise while awake and active or sleep breathing pauses fit BOAS. Marked breathing noise warrants examination.

What does passing an exercise section mean?

It means completing the required activity within time and recovering sufficiently under that scheme. Respiratory severity is assessed separately. Moderate or severe signs can remain despite passing. The vet also assesses nostrils and relative muzzle length.

Can weight loss help breathing?

It can reduce fat around the airways in overweight dogs. Breathing may improve particularly in mild BOAS. An elongated palate may still need shortening. Narrow nostrils can be widened simultaneously.

How well can dogs breathe after surgery?

Surgery can improve breathing and activity tolerance. Signs can remain, especially with permanent laryngeal damage. Close monitoring watches for swelling afterwards. Hospital observation usually lasts at least 24 hours.

What if my dog overheats on a walk?

Stop activity and move somewhere cool. Start cooling immediately, for example with cool water over the body from behind the neck. Call an emergency vet and seek care for suspected heatstroke. Keep water away from the face.