Horse with a runny nose: when should you call the vet?

What is normal nasal discharge?

A healthy horse sometimes has a small amount of clear, watery fluid from the nose — especially after exercise or in cold, dry air. That is completely normal and nothing to worry about. It's only when the discharge changes in colour, consistency or volume, or when other symptoms appear, that it's time to pay closer attention. One nostril that is runny while the other stays dry is already a reason to look more carefully, as it can sometimes point to a localised problem such as a dental issue or a sinus infection.

Yellow, green or bloody: pay attention to colour

The colour of the discharge tells you a great deal. Clear discharge during or after exercise is almost always harmless. Yellow or green mucus indicates a bacterial infection, such as strangles (Streptococcus equi) or a secondary infection following a viral illness. Bloody or reddish-brown fluid can point to exercise-induced pulmonary haemorrhage (EIPH), damaged mucous membranes or a growth in the nasal cavity. Thick, greyish-white discharge from both nostrils at the same time is more commonly associated with a viral upper respiratory infection, such as equine influenza or rhinovirus.

When should you call the vet straight away?

Not sure whether it's urgent? The following signs call for a quick phone check or an immediate visit:

• Yellow or green mucus that persists for more than 2–3 days
• Nasal discharge from only one nostril
• Bloody or reddish-brown fluid
• Fever above 38.5 °C combined with nasal discharge
• Swollen lymph nodes under the jaw (possible strangles)
• Shortness of breath, coughing or reduced appetite
• Foul smell from the nose, which may indicate a dental problem or necrotic tissue

Strangles: contagious and notifiable

Strangles is one of the most contagious equine diseases and is notifiable to the relevant authorities if suspected. It typically begins with fever, followed by thick yellow-green mucus from the nose and severely swollen lymph nodes. Horses can also go through the illness without obvious symptoms and unknowingly become sources of infection. Isolate your horse as soon as you suspect strangles and contact your vet immediately for a throat swab or blood test.

What you can track yourself

The more concrete the information you give your vet, the more targeted their response can be. Keep track of:

• When the runny nose started and whether it came on gradually or suddenly
• The colour and consistency of the mucus, ideally with a photo
• Temperature: measure at least twice a day if an infection is suspected
• Whether other horses in the stable are also showing symptoms
• Recent contact with new horses or attendance at events

EquiSight helps you recognise patterns

In the EquiSight horse profile you can record symptoms, temperature readings and photos with date and time. This gives you an instant overview of whether the nasal discharge is getting worse or improving. EquiCoach recognises patterns in your notes and flags when multiple entries together may point to a specific condition — handy when you're unsure whether to call the vet. You can schedule a consultation or set a vaccination reminder directly from the same overview using the calendar.