Why dogs cough PDF Print E-mail
News - Rubrieke
Wednesday, 24 February 2010 06:39
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In this column veterinarian Dr Liesel van der Merwe provides practical assistance for common problems in companion animals. She is a specialist physician at the Onderstepoort animal teaching hospital and a senior lecturer in the section of small animal medicine. Send your questions to This e-mail address is being protected from spambots. You need JavaScript enabled to view it


Dr Liesel van der Merwe

Dogs often cough. If the cough is transient it is often due to a mild viral infection of the trachea (windpipe) called “kennel cough”. Persistent coughs are more of a problem to diagnose and manage. Pneumonia will not occur unless there is a problem with the lungs’ natural defence mechanisms.

Small breed dogs are especially prone to chronic coughing disorders. The causes are usually related to airway disease. The trachea transports air from the nose and mouth into main bronchi, which split up into smaller and smaller bronchioles in the pattern of a tree with its branches.

Initially these airways are supported by cartilage rings, but at the end they are just muscle. Cough receptors which stimulate cough reflex in response to various stimuli are situated in the throat and where the bronchi start splitting up and the region where the trachea splits into the main bronchi to the left and right lung. The three main causes of coughing in small breed dogs are a collapsed trachea, chronic bronchitis and heart disease.

Collapsed trachea is a weakness in the cartilage rings in certain breeds of dogs. Toy-Poms and Yorkies seem especially predisposed. The cshaped ring keeping the trachea open weakens and starts collapsing from the top part. This means that the lining starts bulging into the air passage space and obstructs airflow.

The harder the dog breathes to move air past this obstruction, the more the trachea will collapse inwards, much like a straw. This also causes inflammation which worsens the coughing. The cough in this disease is called a “goosehonk” cough as it is very harsh. This is a serious condition and can cause death. These dogs initially only cough when excited, but the condition progresses to interference with even normal at-rest breathing.

X-ray images of the chest may show a normal windpipe as the disorder is dynamic, especially in the early stages. Surgical reconstruction of these rings is possible if it is the trachea in the neck which is affected, but requires specialist surgery. Generally therapy is based on decreasing the irritation and inflammation and supporting the breathing muscles.

Chronic bronchitis is probably initially due to allergic disease, but with continued irritation of the airways’ lining, the lining has become thickened, less pliable and with more mucous glands. This cough is also more common when the dog is excited. Once again there is no cure, only control using anti-inflammatories and antitussives (cough suppressants).

Codeine is one of the commonly used cough-suppressants, but unfortunately has the side effect of constipation. Combination therapies with anti-inflammatories can decrease the reliance on any one drug.

These abovementioned conditions affect the natural defence mechanisms in the lungs and can make these dogs predisposed to infection. Dogs with infection often cough up phlegm, which is called a “productive cough”. Obesity worsens both chronic bronchitis and collapsing trachea and weight loss is an essential control measure.

Heart disease can cause coughing for two reasons: the enlarged heart my physically push onto the major bronchi, causing a harsh cough. Or the heart may be failing and a buildup of fluid in the lungs may be the cause of the cough. Dogs in heart failure are usually much less active than the other dogs mentioned here, and often cough at night when they are sleeping.

These dogs are often showing other signs of illness such as weight loss, decreased appetite and exercise intolerance. The cough in these cases is a warning cough and will be controlled if the underlying heart condition is treated. Recurrence of the cough will indicate progression of the heart condition.

Chronic coughing can also result from allergic bronchitis, cancers in the lung, and parasitic infections. Chest X rays are an essential diagnostic tool in any patient with a chronic cough.

Additionally some patients may need to have an endoscopic examination of the air-passages.

The flexible fibre-optic camera allows the clinician to see if the trachea is sagging or if air-passages are being squashed closed by outside pressure as in an enlarged heart.

Sucking some of the cells out of the air-passages for examination under a microscope, whilst the patient is under a general anaesthetic, is also very helpful to determine if the bronchitis is allergic, chronic or infectious.

Coughing is less common in cats. They have more elastic fibres in their air-passages and can develop allergic asthma however, causing severe respiratory distress.

 

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