SYMPTOM
Persistent cough
A persistent cough in a dog is one that continues or keeps returning over weeks instead of settling. It may be harsh and dry, sometimes with a honking sound, or deeper and moist, and bouts can end in gagging or retching. Owners often notice it with excitement, exercise or pressure from a collar, or after rest. Whether a cough arises from the airways, the lungs, the heart or a parasite cannot be judged from its sound at home.
Airway Collapse (Tracheobronchomalacia)
Progressive weakening of the cartilage supporting the trachea and bronchi allows the airway to narrow during breathing, producing a chronic, non-productive cough that worsens with excitement or exercise. Small-breed, overweight, and older dogs are most typically affected.
Chronic Bronchitis
Long-standing inflammation of the airway lining, not attributable to active infection, leads to a persistent cough that tends to worsen with exercise or excitement and is more common in middle-aged and older dogs. Diagnosis usually follows exclusion of infectious and cardiac causes.
Cardiac Disease
Dogs with mitral valve disease or dilated cardiomyopathy can develop a persistent cough. In a study of 206 dogs with mitral valve disease, coughing was associated with an enlarged left atrium and with airway changes on chest X-rays, and not with congestive heart failure itself, so a cough alone does not show whether fluid has built up in the lungs. When the left side of the heart fails, fluid accumulates within the lungs, and difficulty breathing and tiring on exercise are seen alongside any cough. Small breeds such as Cavalier King Charles Spaniels are prone to mitral valve disease, while larger breeds including Dobermanns are more associated with dilated cardiomyopathy.
Lungworm Infection (Angiostrongylus vasorum)
Adult worms live in the pulmonary arteries and the right side of the heart, and the infection causes coughing, laboured breathing and reduced exercise tolerance. It can also cause spontaneous or prolonged bleeding and neurological signs, and bleeding may be the only abnormality noticed, with no cough at all. In a published series of 180 infected dogs, 65 (36.1%) had bleeding, and 76.9% of those dogs survived to hospital discharge against 94.8% of the dogs without bleeding. Dogs acquire the parasite by ingesting slugs or snails. The infection is endemic in the United Kingdom: first clustered in south-west England, South Wales and South East England, it has since been found to be widespread in central England and patchily present in northern England and Scotland.
Eosinophilic Bronchopneumopathy
Infiltration of eosinophils, a type of white blood cell, into the airway lining and lung produces a chronic cough with gagging and retching, which were present in every dog in a published series of 23, with breathing difficulty in 21 of them (91%). A hypersensitivity reaction is suspected, although the precise cause is often unknown. Affected dogs are usually young adults of four to six years, although the condition has been diagnosed in dogs younger than one year and older than ten. A breed predisposition has been described in Siberian Huskies and Alaskan Malamutes, and the condition is also seen in other large breeds such as Labradors, Rottweilers and German Shepherds, and less commonly in smaller breeds. Lungworm can cause a similar eosinophilic lung disease and is looked for before this diagnosis is made.
Why timing matters
Early observation
Several causes of a persistent cough respond to treatment once identified. For lungworm, the ESCCAP UK and Ireland guidance describes safe and effective treatments, and notes that infection can remain without signs for months to years before illness appears.
Later presentation
A cough joined by laboured breathing, a blue or purple tongue or gums, fainting, collapse or unexplained bleeding is of a different order of severity. In a published series of 15 dogs with lungworm whose main complaint was unexplained bleeding, four died, three of them on the day of admission.
Separating airway, lung, heart and parasitic causes of a cough relies on examination and tests such as chest X-rays, heart ultrasound, airway sampling and lungworm testing.
Conditions commonly associated
Angiostrongylus (Lungworm)
Coughing results from larval migration through lung tissue and associated inflammation.
Dilated Cardiomyopathy in Dogs
In dilated cardiomyopathy the weakened heart muscle pumps poorly, and coughing is among the reported signs, alongside difficulty breathing, episodes of weakness, fainting or collapse, and fluid accumulating in the chest or abdomen.
Pneumonia
Pneumonia causes persistent cough as the lungs respond to inflammation and infection, often producing mucus or fluid that the body attempts to clear. The cough in pneumonia tends to appear alongside other signs of respiratory distress and systemic illness.
Laryngeal Paralysis in Dogs
In laryngeal paralysis the larynx does not open fully during breathing, and coughing and gagging are among the reported signs. The cough may accompany characteristic voice changes and increased respiratory effort, particularly during exertion or heat.
Eosinophilic Bronchopneumopathy
Eosinophils infiltrating the airway lining in this condition irritate the bronchi, producing a cough that persists for weeks rather than clearing.
Mitral Valve Disease in Dogs
Mitral valve disease is more common in older, small-breed dogs. In affected dogs a cough has been linked to enlargement of the left atrium and to airway changes, and it does not by itself show that heart failure is present.
Chronic Bronchitis in Dogs
Chronic bronchitis is defined by a cough lasting at least two months that is not due to another respiratory disease, so it is diagnosed once other causes have been excluded.
Tracheal Collapse in Dogs
Weakening of the cartilage rings lets the windpipe flatten, producing a harsh, dry, honking cough brought on by excitement, exercise or pressure on the neck, most often in middle-aged or older small-breed dogs.
When to explore further
When the cough continues for weeks or is becoming more frequent
When the cough is accompanied by laboured or noisy breathing, a blue or purple tongue or gums, fainting or collapse, which can reflect heart failure or an obstructed airway and cannot be assessed at home
When the dog tires more easily on walks, is lethargic, or loses appetite or weight
When there is unexplained bruising or bleeding, such as nosebleeds or bleeding in the mouth, because lungworm can cause fatal bleeding even in a dog with no respiratory signs
Noting when this symptom occurs, any triggers, and how it changes over time can provide useful information for veterinary discussions.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS