Nasal Discharge in Horses: Causes, Risks & Related Conditions

It’s not unusual to see a small amount of clear, watery discharge coming from your horse’s nose — especially after exercise, during cold weather, or when they’ve been around dust or pollen. Mild discharge is part of the body’s natural defense system, helping keep the nasal passages moist, trapping debris, and protecting against harmful particles in the air.

Sometimes, a horse’s runny nose can mean something more serious. Nasal discharge that is thick, yellow, green, or has an unpleasant odor may be a sign of infection or another health problem. Blood in the discharge or drainage from only one nostril are also red flags that shouldn’t be ignored.

Nasal discharge in horses may arise from infectious causes like viral or bacterial respiratory diseases or from non-infectious issues such as dental infections, trauma, or airway obstruction. Horses with nasal discharge may also have signs of fever, coughing, reduced appetite, or lethargy.

Learn to identify different types of nasal discharge in horses, what they mean, and how to manage underlying conditions. You’ll also find tips on prevention, quarantine, and when to call the veterinarian if your horse shows signs of illness.

Nasal Discharge in Horses

How do you know if your horse’s runny nose is normal or a sign of illness? Under normal conditions, horses may have a small amount of clear, odorless, watery nasal discharge, especially after exercise or exposure to dusty environments.

This mucus moistens the nasal passages, traps dust and debris, and provides a first line of defense against inhaled pathogens.

Normal nasal discharge is typically bilateral, meaning it comes from both nostrils, and is minimal in volume. A temporary increase in the amount of discharge may be caused by: ^[1][2]

• Seasonal environmental changes
• Increased physical exertion
• Exposure to allergens

Healthy nasal secretions are typically not accompanied by other symptoms, such as coughing, fever, or appetite loss.

Assessing Nasal Discharge

It is important to monitor any changes in the color, volume, or consistency of nasal discharge, as these may signal the early stages of infection or inflammation. If discharge becomes persistent, changes in color, or is associated with other clinical signs, veterinary evaluation is recommended to rule out underlying health concerns.

The characteristics of nasal discharge provide valuable clues about its cause and severity. Careful attention to which nostril is affected, the color, odor and texture of the discharge can guide initial diagnosis and treatment planning.

Below is a quick guide to assessing the characteristics of your horse’s nasal discharge.

Table 1. Characteristics of Equine Nasal Discharge ^[1][3][4]

Associated Conditions

Nasal discharge in horses can arise from a range of underlying conditions that affect the respiratory tract or surrounding structures. Identifying the root cause is essential for selecting the most effective treatment and preventing further complications.

These conditions can be broadly categorized into infectious and non-infectious origins, each with distinct clinical features and implications for management.

“Any unexplained nasal discharge in a horse deserves attention. Discharge that is colored, thick, and/or malodorous often signals infection or other serious issue. Blood coming from one or both nostrils always requires urgent veterinary attention. Prompt diagnosis and treatment are key to keeping your horse healthy.”

— Dr. Fran Rowe DVM, PAS
Mad Barn Veterinary Nutritionist

Understanding these categories can help guide the diagnostic process and inform appropriate interventions for horses with a runny nose.

Infectious Conditions

Infectious diseases are a common cause of nasal discharge in horses. Viral, bacterial, or mixed infections can affect the upper or lower respiratory tract, producing varying degrees of discharge depending on the pathogen and severity of the illness.

Viral Infection

Viruses can cause a wide variety of symptoms in horses. However, most common equine viruses have overlapping symptoms of immune system activation within the respiratory system, including fever, increased nasal discharge and coughing.

Common viral infections in horses include: ^[4][5][6][7]

• Equine Influenza: Highly contagious strains of the influenza A virus characterized by a sudden onset of high fever, harsh dry cough, muscle soreness, lethargy, and nasal discharge that starts as serous (watery) and may progress to a thicker, mucoid consistency.
• Equine Herpesvirus (EHV-4): Also called rhinopneumonitis, EHV-4 infection primarily affects young horses and is a frequent cause of respiratory disease outbreaks. Symptoms of EHV-4 infection are similar to those of influenza, including fever, increased clear or watery nasal discharge, coughing, and enlarged lymph nodes below the jaw.
• Equine Viral Arteritis (EVA): Horses with EVA typically exhibit fever, swelling of the limbs and underbelly, pink-eye, and a watery or thick nasal discharge. The EVA virus is less widespread than equine influenza and herpesviruses, but can be sexually transmitted or spread by coughing. Pregnant mares may abort if affected by EVA.

Vaccination is critical for preventing viral infections, especially in young or traveling horses. Identifying the specific virus can be difficult and often requires blood tests. ^[4][5]

Bacterial Infection

Viral infections strain the immune system, potentially allowing small populations of internal bacteria to grow unchecked. When this happens during a viral illness, it’s known as a secondary bacterial infection.

Common bacteria associated with secondary infections in horses include: ^[4]

• Streptococcus zooepidemicus
• Actinobacillus equuli
• Bordetella bronchiseptica
• Pasteurella spp.

Signs of a secondary bacterial infection include worsening nasal discharge — typically thick, yellow, or green — along with ongoing fever, coughing, fatigue, and abnormal lung sounds on auscultation. ^[4]

Diagnosis may involve airway sampling and culture. Treatment generally requires targeted antibiotic therapy and supportive care to resolve the infection and support respiratory function. ^[4]

While viral infections increase the risk of secondary bacterial infections, primary bacterial infections (those occurring without a preceding virus) are also fairly common in horses. ^[4]

Strangles

Strangles is a highly contagious bacterial infection of the upper respiratory tract, caused by Streptococcus equi bacteria. Horses with Strangles often develop fever, lethargy, swollen and abscessed lymph nodes (especially around the jaw and throat), and pus-like nasal discharge.

Strangles can lead to an accumulation of pus within the guttural pouches (spaces between the nose, throat and inner-ear), called guttural pouch empyema or “bastard strangles“. ^[8]

Horses with guttural pouch empyema may show difficulty swallowing, enlarged lymph nodes and coughing. Diagnosis is confirmed through endoscopy (a visual inspection of the nasal passages and throat using a camera).

Treatment typically involves repeated cleaning of the guttural pouches and systemic antibiotics, though chronic cases may require surgery. ^[9]

Tooth Root Abscess

Tooth root abscesses are a common cause of unilateral, foul-smelling purulent nasal discharge in horses.

Infections typically involve teeth near the upper cheek, whose roots are closely associated with the maxillary sinus. When an abscess breaches the sinus, bacteria and pus accumulate, leading to discharge through the nasal passages. ^[4]

Affected horses may also show signs of facial swelling, reluctance to chew, weight loss, and pain upon palpation of the jaw or face.

Diagnostic imaging and dental examination are essential for diagnosis, and treatment usually involves extraction of the affected tooth and sinus drainage. ^[4]

Non-Infectious Conditions

While infectious diseases are a major cause of nasal discharge in horses, several non-infectious conditions can also lead to abnormal nasal secretions. These conditions are often related to physical obstructions, tissue damage, allergic responses, or tumor growths within the respiratory system.

Unlike infectious diseases, non-infectious conditions may not always be accompanied by fever or systemic illness, but they can still cause significant discomfort and health risks if left untreated. Accurate diagnosis often requires imaging studies, endoscopy, and in some cases surgical exploration.

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Head Injury

Trauma to the skull or sinuses, such as from a fall, kick, or collision, can lead to hemorrhagic (bloody) nasal discharge. Fractures of the skull bones or damage to the sinuses can result in bleeding into the nasal cavity. ^[10]

In some cases, the longus capitis muscle at the base of the skull is torn during head trauma, which causes bleeding into the guttural pouches.

Horses whose nasal discharge is associated with trauma should be evaluated with imaging studies to assess the extent of injury and monitor for secondary complications such as infection or nerve damage. ^[10][11]

Equine Asthma

Equine asthma, which often manifests as “heaves,” is a chronic allergic respiratory disease. Horses with equine asthma frequently present with bilateral nasal discharge that is serous to mucoid in consistency, along with a chronic cough and increased respiratory effort, particularly in dusty or moldy environments. ^[12]

Managing equine asthma involves reducing environmental allergens, using dust-free bedding and soaked hay, and administering pharmaceutical bronchodilators or corticosteroids when necessary. ^[12]

Choke

Choke occurs when food becomes lodged in the esophagus, preventing normal swallowing. Horses experiencing choke often have nasal discharge contaminated with saliva, water, and feed material. ^[13]

In cases where the obstruction persists, secondary aspiration pneumonia may develop, leading to additional thick, foul-smelling nasal discharge. Prompt veterinary intervention is needed to resolve choke episodes and prevent further respiratory complications. ^[13]

Exercise-Induced Pulmonary Hemorrhage (EIPH)

EIPH is a condition commonly observed in performance horses, particularly those engaged in intense activities such as racing, eventing, or barrel racing. It is characterized by bleeding from the lungs during or immediately after strenuous exercise, leading to bilateral, blood-tinged nasal discharge in some cases.

However, not all horses with EIPH exhibit visible bleeding at the nostrils (epistaxis), as much of the blood may remain within the lower airways. ^[14]

The exact cause of EIPH is not fully understood, but it is believed to involve high pulmonary blood pressure and stress-induced rupture of delicate blood vessels in the lungs. Diagnosis is typically confirmed via endoscopy following exercise, revealing blood in the trachea or bronchi. ^[14]

While EIPH does not usually present with systemic signs of illness, it can negatively impact performance and may require management strategies such as rest, the use of furosemide (Lasix®), and adjustments in training intensity or surface conditions. ^[14]

Diagnostics

Accurate diagnosis of the cause of your horse’s runny nose is important for treatment. Veterinarians typically use one or more of the following diagnostic techniques when investigating nasal discharge in horses: ^[4]

• Physical Exam: A thorough physical exam includes evaluating the type, color, and location of the discharge.
• Endoscopy: Visual inspection of the upper airway is the gold standard for directly visualizing abnormalities such as guttural pouch disease, ethmoid hematomas, or sinusitis.
• Diagnostic Imaging: Imaging techniques including radiographs (X-rays) and ultrasound can help identify dental disease, sinus masses, or fluid accumulation.
• Culture and Cytology: Sampling techniques like nasopharyngeal swabs, guttural pouch washes, bronchoalveolar lavage, or sinus aspirates allow for cytology and culture to identify infectious agents. Blood work, including complete blood counts and fibrinogen levels, can aid in determining the severity and systemic involvement of infections.

Ultimately, clinical signs, imaging, endoscopy, and laboratory testing together provide the best chance of identifying the cause and choosing an appropriate treatment plan.

Prevention & Environmental Management

Proactive stable management is key to preventing nasal discharge associated with respiratory illness in horses. Recommended strategies include:

• Ventilation: Ensure barns are well-ventilated to reduce dust, ammonia, and airborne pathogens.
• Dust control: Use dust-free bedding and soaked hay to minimize inhaled irritants.
• Vaccination: Maintain up-to-date vaccines against common equine viruses including influenza, herpesvirus, and strangles.
• Biosecurity: Adhering to appropriate quarantine, handling, and sanitization protocols during travel and when introducing new horses helps control the spread of infectious disease.
• Monitoring: Regularly observe horses for early signs of illness. Prompt isolation of affected horses can limit outbreaks.

Finally, a well-balanced, forage-first diet goes a long way to support your horse’s healthy immune responses. If you are unsure whether your horse’s diet is meeting their immune system needs, book a free consultation with one of our expert equine nutritionists today.

Frequently Asked Questions

Here are some frequently asked questions about nasal discharge in horses:

Summary

Nasal discharge in horses can range from a harmless physiological response to an indicator of serious disease. Careful assessment of the discharge's characteristics helps narrow down potential causes.

• Discharge characteristics such as texture, color, and localization can help determine when to call your veterinarian
• Equine influenza, herpesvirus, and strangles are common infectious conditions associated with nasal discharge and other symptoms of illness
• Non-infectious conditions such as dental infections, injuries, and EIPH are also possible causes
• Prevention through environmental control, vaccination, and early quarantine of affected horses help maintain herd health