Equis ISSN 2398-2977


Contributor(s): Tim Brazil, Nicola Menzies-Gow, Graham Munroe


  • Sudden explosive expulsion of air through the glottis.
  • Cough is a sign NOT a diagnosis.
  • Cause: common sign of many respiratory tract diseases; reflex pulmonary defense mechanism.
  • Signs: coughing of different types, periodicity, association with other clinical signs, relationship to exercise.
  • Diagnosis: full physical examination; use of multiple ancillary aids.
  • Treatment: depends on etiology.
  • Prognosis: depends on etiology.



Upper respiratory tract

Viral infections

Bacterial infections

  • Streptococcus equi equi(strangles)   Streptococcus spp  .
  • Streptococcus equi zooepidemicus.

Physical deformities

Neurological abnormalities

Increased exudate


  • Food aspiration.

Lower respiratory tract


Lung abscesses



Cardiovascular disease

  • Pulmonary edema.
  • Left heart failure.
  • Congestive heart failure.
  • Cor pulmonale.
  • Endocarditis   Heart: endocarditis  .
  • Tetralogy of fallot.

Allergic/irritant reaction


  • Inflammatory airway disease (IAD).



  • A sudden explosive expulsion of air through the glottis.
  • Facilitates removal of noxious substances and excessive secretions from airways by maximizing airflow velocity.
  • There are 4 phases to the cough cycle: inspiration, compression, expression and relaxation.
  • Most effective as a defense mechanism for clearing large airways but less so in obstructive diseases of the small airways.
  • The sound of a cough is generated by laryngeal/pharyngeal structure vibration, narrowing and deformation of airways and by surrounding lung tissue vibration. Variations in sounds are most likely related to the quantity and quality of airway mucus.
  • The afferent input for the cough reflex is predominantly carried in the vagus nerve. Sensors in the larynx respond to mechanical and chemical irritation and via myelinated nerves mediate both coughing and airway diameter changes (bronchoconstriction). Receptors in the lower airway are located at the carina (mechanical deformation, eg mucus, inhaled particles) and peripheral airways (chemical irritants, eg inflammatory mediators).
  • Coughing may be stimulated in a number of ways:
    • Airway smooth muscle contraction (bronchoconstriction).
    • Excessive mucus production.
    • Presence of inhaled particles in airways.
    • Release of inflammatory mediators.
    • Exposure to hot or cold air.
    • Intramural/extramural pressure or tension on the airways, eg tumor, granuloma, abscess, pleuritis.
    • Sloughing of airway epithelial cells.
    • Enhanced epithelial permeability (pulmonary edema).
  • diseases of the respiratory tract may alter the sensitivity of the cough reflex, eg post-viral infections.
  • There are deleterious consequences of coughing, especially when intense, chronic or constant:
    • Chronic coughing is exhausting and may decrease food intake.
    • Persistent coughing may impair respiration.
    • Effects on cardiovascular system especially hypotension.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Head M J & Wook J L N (2001) Coughing - a source of irritation? Equine Vet J 33 (3), 221-223 PubMed.
  • McKane S A et al (1993) Equine bronchoalveolar lavage cytology - survey of Thoroughbred racehorses in training. Aust Vet J 70 (11), 401-404 PubMed.
  • Hoffman A M et al (1993) Association of microbiologic flora with clinical, endoscopic and pulmonary cytologic findings in foals with distal respiratory tract infection. Am J Vet Res 54 (10), 1615-1622 PubMed.
  • Hoffman A M et al (1993) Clinical and endoscopic study to estimate the incidence of distal respiratory tract infection in Thoroughbred foals on Ontario breeding farms. Am J Vet Res 54 (10), 1602-1607 PubMed.
  • Vrins A et al (1991) A restrospective study of bronchoalveolar lavage cytology in horses with clinical findings of small airway disease. Zentralbl Veterinarmed A 38 (6), 472-479 PubMed.
  • Collins A (1986) Coughing horses. Vet Rec 119 (7), 162-163 PubMed.
  • Brown C M (1983) Tracheobronchial foreign body in a horse. JAVMA 182 (3), 280-281 PubMed.