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Coughing is a normal protective reflex designed to clear the airways of foreign material . It is controlled through afferent and efferent nerves to a cough centre in the brain and the reflex is triggered by several forms of stimuli including chemical and physical causes.

Stimulation of the cough reflex is accompanied by increased mucus secretion, and this moves material up the airway by ciliary action (small hairs lining the respiratory tract) from the lower bronchioles, up the bronchi and trachea and through the larynx into the oropharynx. From the pharynx material can be coughed out of the mouth, but it is usually swallowed.

Many disease processes cause coughing in which case it my not be acting as a protective mechanism but becomes a futile reflex, and if untreated it may cause unnecessary damage to the respiratory tract.

There are numerous causes of coughing, some of the most common are:

  • Foreign material entering the airways (food, drink)
  • Inflammation - infections (e.g. kennel cough in dogs), smoke, chronic bronchitis
  • Compression of airways - heart disease, cancer
  • Collapse of airways - tracheal collapse in toy breeds of dog
  • Excess mucus secretion
  • Trauma causing haemorrhage
  • Other causes of pulmonary haemorrhage e.g. warfarin poisoning
  • Causes of pulmonary oedema - e.g. acute cardiac failure

Pink-tinged white frothy mucus is typical of haemorrhage into the respiratory tract.

The character of the cough may help in diagnosing the underlying cause.

A productive cough is one in which mucus and other material is coughed up from the respiratory tract. This is typical following aspiration of foreign material into the airways (as occurs in megaoesophagus, or in pneumonia).

A non-productive cough is one in which material is not brought up. This is typical of local stimulation of a cough from the pharynx - e.g. local irritation from a foreign body, or inflammation associated with local infections.

A dry harsh or hacking cough (which owners often confuse as a foreign body stuck in the throat) are typical of inflammation of the large airways and trachea, and are typical of tracheobronchitis , such as occurs with bordatella bronchiseptica infection (called "kennel cough" in dogs).

A honking-sounding cough is typical of collapse of the trachea and of inhaled foreign bodies in the trachea.

Quieter, soft coughs (often sound like the animal is "clearing it's throat" ) are often associated with pneumonia, pulmonary oedema, compression of the airways by an enlarged heart in cardiac failure and the presence of lung cancer.

All forms of cough are worse during exercise or when a recumbent animal changes position - such as during sleep, or upon awakening and starting to move around.

Cough suppressants should only be used when the cough reflex is not being beneficial. The underlying cause of the cough should be treated e.g. antibiotics for bacterial infections, medications for heart failure.


Last updated : October 2013