Bit & Bridle

Equine Nasal Discharge

Other Names

  • Nasal exudate
  • Nasal secretion
  • Epistaxis (nosebleed — when discharge is haemorrhagic)
  • Catarrhal discharge

What is Nasal Discharge in Horses?

Nasal discharge refers to the production and release of fluid from one or both of a horse’s nostrils. While a small amount of clear, watery discharge is normal — particularly during or after exercise — abnormal nasal discharge is one of the most common presenting signs in equine practice and can indicate a wide range of conditions, from minor viral infections to serious life-threatening disease.

Characterising the discharge is the first step in understanding its significance. The key variables are: whether it is unilateral (one nostril) or bilateral (both nostrils), the consistency and colour (clear, white, yellow-green, blood-tinged, or frankly haemorrhagic), the volume, any associated smell, and whether it occurs at rest, during exercise, or when the head is lowered.

Unilateral discharge more often suggests a localised problem on that side — sinus disease, dental disease, a foreign body, or a mass — while bilateral discharge is more typical of systemic respiratory infections or lower airway disease. Foul-smelling discharge often indicates bacterial infection or necrotic tissue. Haemorrhagic discharge from one nostril at rest warrants urgent investigation. For related respiratory conditions, see our entry on Equine RAO.

Causes

The causes of equine nasal discharge are broad. The most common include:

  • Viral respiratory infections — equine influenza, equine herpesvirus (EHV-1 and EHV-4), and equine rhinitis viruses commonly cause bilateral serous to mucopurulent nasal discharge, usually alongside fever and coughing
  • Bacterial infections — Streptococcus equi (strangles) classically causes thick, purulent unilateral or bilateral discharge alongside submandibular lymph node swelling and fever; secondary bacterial sinusitis produces unilateral, often foul-smelling discharge
  • Sinusitis — primary or secondary inflammation of the paranasal sinuses, often producing unilateral, purulent, or malodorous discharge. Secondary sinusitis from dental root disease (particularly cheek teeth) is common in horses over eight years of age.
  • Dental disease — infection or abscessation of the maxillary cheek teeth roots can drain into the caudal maxillary sinus, producing unilateral discharge with a characteristic fetid smell
  • Guttural pouch disease — the guttural pouches are large air-filled diverticula of the Eustachian tubes; empyema (pus-filled) or mycosis (fungal infection) of the guttural pouch produces unilateral discharge that may be purulent, blood-tinged, or frankly haemorrhagic. Guttural pouch mycosis can cause life-threatening epistaxis.
  • Equine asthma (RAO) — typically causes bilateral mucopurulent discharge, often with coughing and respiratory effort
  • Exercise-induced pulmonary haemorrhage (EIPH) — blood from ruptured pulmonary capillaries during intense exercise; typically bilateral but may present as epistaxis post-exercise
  • Foreign bodies — grass seeds, feed material, or other objects lodged in the nasal passage can cause unilateral, often malodorous discharge
  • Nasal polyps or tumours — progressive unilateral discharge, often with nasal deformity, progressive obstruction, and sometimes facial swelling

Symptoms and Signs

The character of the discharge guides the clinical assessment:

  • Clear, watery (serous) — often normal post-exercise; in resting horses may indicate viral infection, early allergen exposure, or environmental irritation
  • White, frothy — often associated with lower airway disease or RAO
  • Yellow-green, thick (mucopurulent) — indicates bacterial infection; note whether unilateral or bilateral
  • Foul-smelling — strongly suggests sinusitis, dental root abscess, or necrotic tissue
  • Blood-tinged or frank haemorrhage — can arise from EIPH, guttural pouch mycosis, trauma, tumour, or clotting disorders; any significant haemorrhage warrants urgent veterinary attention

Associated signs such as fever, coughing, lymph node enlargement, facial swelling, weight loss, or respiratory distress help narrow the differential diagnosis considerably.

Diagnosis

The diagnostic workup depends on the character and duration of the discharge:

  • Physical examination — observation of the discharge character, palpation of submandibular and parotid lymph nodes, percussion of the sinuses, and assessment of the oral cavity and teeth
  • Endoscopy (nasopharyngoscopy) — visualisation of the nasal passages, nasopharynx, guttural pouch openings, larynx, and trachea; essential for locating the source of discharge and sampling material for culture
  • Guttural pouch endoscopy — direct entry into the guttural pouches to assess for empyema, mycosis, or other pathology
  • Radiography — useful for assessing sinus opacification, dental roots, and the presence of masses or fluid lines within the sinuses or guttural pouches
  • Computed tomography (CT) — increasingly available at equine referral centres; provides superior detail of sinus and dental anatomy and is highly useful for surgical planning
  • Bacteriological culture and sensitivity — from swabs or washes of the nasal passage, guttural pouch, or sinus, to guide antibiotic selection
  • Strangles serology (ELISA) — blood test for antibodies to S. equi; useful for confirming recent infection or carrier status

Treatment

Treatment is directed at the underlying cause:

  • Viral infections — supportive care (rest, ensure adequate hydration, nutritional support); antibiotics are not indicated for viral disease but may be used if secondary bacterial infection develops
  • Strangles — controversial: antibiotics may limit the extent of infection but can interfere with natural immunity development. Abscesses are best managed by encouraging drainage. Strict biosecurity and isolation are essential. BEVA publishes consensus guidelines on strangles management.
  • Sinusitis — antibiotic therapy for primary sinusitis; surgical debridement (sinus flushing or trephination) for secondary sinusitis or cases unresponsive to medical treatment. Dental extraction may be required for dental-origin sinusitis.
  • Guttural pouch empyema — flushing of the pouches with saline via endoscopy or catheter; mucolytics to break down chondroids; surgery for impacted chondroids
  • Guttural pouch mycosis — antifungal treatment combined with surgical occlusion of affected arteries to prevent fatal haemorrhage; referral to a specialist centre is strongly recommended
  • Foreign bodies — endoscopic or surgical removal

For further guidance on equine respiratory conditions, the BEVA provides clinical guidelines at beva.org.uk.

Prevention

Reducing the risk of nasal discharge-causing conditions involves:

  • Vaccination against equine influenza and equine herpesvirus — up to date vaccination is the single most effective preventive measure for viral respiratory disease
  • Biosecurity — isolation of new horses arriving at a yard for at least three weeks; testing for strangles carrier status before introducing horses to a new herd
  • Regular dental examinations — six-monthly or annual dental checks detect early cheek tooth root disease before sinusitis develops
  • Environmental management — reduce dust and mould exposure to limit allergen-driven airway disease
  • Monitor all horses daily — early detection of abnormal discharge allows prompt investigation and prevents spread

Prognosis

Prognosis depends entirely on the underlying cause. Viral respiratory infections in otherwise healthy, vaccinated horses typically resolve within two to three weeks with appropriate rest. Bacterial sinusitis responds well to treatment in most cases but may require surgery in advanced cases. Guttural pouch mycosis carries a guarded to poor prognosis without specialist surgical intervention, as the risk of fatal arterial haemorrhage is significant. Nasal tumours vary widely in prognosis depending on type and extent.

When to Call the Vet

  • Nasal discharge is persistent for more than a few days
  • Discharge is thick, coloured, or malodorous
  • Significant volumes of blood are coming from one or both nostrils
  • Discharge is accompanied by fever, swollen lymph nodes, coughing, or weight loss
  • Multiple horses on a yard are showing similar signs simultaneously — this warrants urgent investigation and biosecurity measures

Frequently Asked Questions

Is a small amount of clear discharge normal in horses?

Yes — a small trickle of clear, watery discharge, particularly after exercise or when the head is lowered, is normal and relates to normal mucociliary clearance of the upper airways. It is when discharge is persistent, coloured, foul-smelling, or accompanied by other signs that investigation is warranted.

What is strangles, and how does it spread?

Strangles is a highly contagious bacterial infection caused by Streptococcus equi subspecies equi. It spreads via direct contact with infected horses, shared water troughs and feed buckets, or contaminated hands and equipment. Some horses become long-term silent carriers following infection — they shed bacteria from the guttural pouches without showing signs and can infect naive horses. Testing for carrier status is essential before reintroducing recovered horses to a herd.

What is guttural pouch mycosis, and is it serious?

Guttural pouch mycosis is a fungal infection of the guttural pouches, most commonly caused by Aspergillus species. The fungal plaques grow on the walls of the pouches in close proximity to the internal carotid artery. Erosion of the arterial wall can cause sudden, severe, life-threatening haemorrhage. It is a serious emergency requiring referral to a specialist equine surgical centre.

How can I tell if my horse has sinusitis?

Typical signs of sinusitis include persistent unilateral nasal discharge (often mucopurulent or malodorous), facial asymmetry or swelling over the sinus region, dull percussion over the affected sinus, and occasionally reduced airflow from the affected nostril. Your vet can confirm sinusitis with radiography, endoscopy, or CT imaging. See our horse terminology guide for equine sinus anatomy.