Lower Respiratory Disease In Horses

Lower respiratory disease is one of the most common complaints that we see in our patient’s day to day.

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They can affect horses of any age and breed, and as such, it is important to be able to identify signs of a possible problem early on.

What Symptoms Should I Look For?

Common symptoms include:

  • Nasal discharge
  • Coughing
  • Flared nostrils
  • Increased respiratory rate and effort
  • Exercise intolerance
  • Lethargy
  • Abnormal respiratory noise
  • Swollen lymph nodes
  • Inappetence

Diagnosing Equine Lower Respiratory Disease

Many lower respiratory diseases have very similar presenting signs. As such, a thorough history and clinical exam are essential. Although this can often be enough for a diagnosis, sometimes further tests will be required.

Blood Samples

Blood samples can help us to diagnose infectious diseases such as strangles, flu or herpes. Often two samples taken two weeks apart are needed to rule these in or out.

Nasopharyngeal Swabs

Can be useful for identifying infectious causes.


Fig. 1

Allows us to visualise the airways and identify signs of inflammation or infection. Samples of the cells can be taken from the guttural pouches, trachea and alveoli, which can help us reach a definitive diagnosis more easily.

Fig. 1 shows an endoscopic image of normal lower trachea leading into the bronchi. Image courtesy of: michaelporterdvm.blogspot.com

Common Causes & Treatments Of Lower Respiratory Diseases

Equine Asthma (historically known as COPD)

The most common respiratory disease that we see, more often affecting the older horse. Equine asthma is caused by an inflammatory reaction to allergens in the environment resulting in constriction of the affected animals’ airways, often resulting in a characteristic ‘wheeze’ heard on exhalation.

The allergens that cause it can be almost anything, but most frequently are pollens, fungal spores in forage and dust. We often see a seasonal pattern to symptoms depending on the allergen responsible.

Treatment involves medical therapy with steroids for their anti-inflammatory properties and/or Ventipulmin to dilate the constricted airways. These can be given orally or by an inhaler. Removing the horse from suspected allergens is just as important as drug therapy. For example, using dust extracted bedding and soaking hay in cases where dust may be implicated.


Fig. 2

Caused by bacteria, strangles is extremely infectious and, as such, passes easily from horse to horse. Lethargy, pyrexia (high temperature) and swollen lymph nodes between and behind the jaw are the classic symptoms seen, however, symptoms can vary greatly from causing none at all to multi-organ failure in the most serious cases.

Most cases will resolve on their own so treatment is usually focused on nursing care of the affected individuals, anti-inflammatories and most importantly isolation from unaffected horses to prevent further spread. Vaccines do exist for strangles, however adverse reactions and questionable efficacy means its use is not widespread.

Fig. 2 Swelling under jaw characteristic of strangles

Viral Diseases

There are many viral causes of respiratory disease in the horse, the most common of which are equine influenza and equine herpes virus (EHV) 1 and 4. Lethargy, coughing and pyrexia are common symptoms seen, with EHV 1 also able to cause abortion and neurological signs as well. Young horses are most at risk, particularly those kept in poorly ventilated stables in large groups.

Treatment again resolves around nursing care, anti-inflammatory treatment and isolation to prevent further spread of the disease. There have been widespread outbreaks of flu recently and it is recommended that you get your horse vaccinated. Being vaccinated does not completely remove the risk of getting flu, however does reduce the chance and decreases the severity of clinical signs seen in affected animals.

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