Horses are obligate nasal breathers – this means they must breathe through their nose as their normal anatomy prevents them from breathing through their mouth. A nasal discharge can be a good indicator of an ongoing problem within the respiratory, or occasionally the gastrointestinal system, and is a common complaint, though not specific to any age or breed of horse or pony.
If your horse has a runny nose what could this mean? When investigating a nasal discharge, along with taking a thorough history and doing a full clinical examination, we think about three main issues; whether the discharge is unilateral or bilateral (is it coming from one or both nostrils), the nature of the discharge (colour, consistency and smell) and thirdly additionally whether the discharge is present at rest or after exercise. The answers to these questions can quickly point us in the direction of where the problem may lie.
Firstly, a basic understanding of the anatomy of the horses’ respiratory system allows us to understand how nasal discharges can arise. From the entrance to the nostrils, the horses’ nasal cavity is divided into two sides by a midline nasal septum. Where the nasal septum ends, the two chambers combine to form a common area called the nasopharynx, separated from the oral cavity by the soft palate. The larynx is the opening to the trachea or ‘windpipe’ which then continues down to the lungs. This is situated at the back of the nasopharynx along with the opening to the oesophagus. Surrounding the nasal cavity, within the horses’ skull, are a complex network of chambers called sinuses, which drain into the nasal cavities through small openings. Some of the sinuses also contain the tooth roots of some of the cheek teeth. As so many structures use the nostrils as an exit point, it is easy to see why runny noses occur so frequently!
Is the discharge unilateral or bilateral?
It seems simple but the location of the lesion can be greatly narrowed down by this. A horse with a persistently unilateral (one sided) discharge will usually have a problem in the nasal cavities or the nasal sinuses of that side. A horse with a bilateral nasal discharge will likely have a lesion further back, beyond the boundary of the nasal septum, in an area shared by both nasal passages, such as the back of the throat or the lungs.
What is the nature of the discharge?
A nasal discharge can vary from a slight, clear drip, to a profuse, foul smelling heavy discharge, perhaps containing blood or food material. It is normal in a lot of horses to have a slight clear discharge after exercise. However, infection and inflammation may be the cause of a thicker, more discoloured and foul-smelling discharge. These discharges may be light and not too noticeable at rest, but as the horse is exercised, the discharge often becomes more profuse and may even cause the horse to cough.
Infection of the sinuses can be primary or secondary to other issues, usually a tooth root infection. Clinical signs may also include the horse becoming head shy and appearing ‘off colour’. The guttural pouches may harbour fungal or bacterial infections, such as seen with 'Strangles'. 'Strangles' is caused by the bacterium Streptococcus Equi Equi, which often causes abscesses in the lymph nodes that burst into the nasopharynx. This will then drain out down through the nose, giving the classic snotty nose signs 'Strangles' is infamous for. Occasionally cancerous growths can occur within the nasal passages. Although uncommon, when diagnosed these have a poor prognosis. The growth of the tumour causes discomfort along with death of surrounding tissue, resulting in a chronic often blood tinged, purulent discharge.
Food can be seen coming down the nose when there is an obstruction further down the gastrointestinal tract. A commonly seen cause of this in practice is oesophageal obstruction or 'choke' when food becomes lodged within the oesophagus, preventing more food or saliva from passing into the stomach. This is often caused by horses gorging on dry feed. Occasionally the pharynx and larynx may have neurological issues when they do not swallow effectively resulting in the reflux of food. This may happen after problems in the guttural pouches or with liver disease. A complication of all of these instances where food is refluxed (or unable to pass into and down the oesophagus effectively), is that the patient is at risk of aspiration pneumonia. This can be a serious, and if severe enough can be fatal condition where food material is aspirated into the lungs and causes infection.
The respiratory system and associated structures of a horse are very vascular and for this reason blood can occasionally be seen alone or within a nasal discharge due to several reasons. Exercised Induced Pulmonary Haemorrhage, or EIPH, is a common problem encountered in racehorses and higher level Eventors, where bleeding occurs in the lungs after high intensity exercise. Any trauma, such as after nasogastric intubation, can result in bleeding.
Once we have gathered the relevant information, there are a variety of techniques we use to further diagnose what is going on. Diagnostics in the laboratory such as blood work, taking a swab of the discharge for bacterial culture and sensitivity are helpful. Additionally, imaging modalities such as radiography, endoscopy, ultrasound and computerised tomography(CT) scan are frequently used to get a full picture of what the cause of the nasal discharge may be and help us formulate the best treatment plan with you the client.
If your horse is suffering from a nasal discharge, please contact the Hospital on 01555 660000 to discuss this matter fully.