Coughing in horses: Is it always a sign of respiratory disease?

Coughing in horses: Is it always a sign of respiratory disease?

Coughing is a common complaint from owners and most horse owners are familiar with their horses giving a few coughs at the start of exercise, but it is not always a sign of respiratory disease in horses.

Why do horses cough and when is it an indication of something more serious or underlying?

Coughing is an indication of mechanical or irritant stimulation of specialised receptors along the entire respiratory tract of the horse. A cough is initiated when these receptors are stimulated and the potential causes for stimulation are diverse. Each one of these receptors has the ability to react to a particular stimulant – whether that stimulant be cold air, dust, mould or mucous. The sensitivity of these receptors varies between horses, in other words, some horses may tolerate a dusty environment whereas others may start coughing with even the slightest provocation.

Coughing in my horse: when should I panic?

Even though a coughing horse seems to always get your attention, it is important to remember that the sound and intensity of the cough does not necessarily tell you how significant it is. Most coughing attempts are simply an effort to clear irritants from the respiratory tract. Should a cough be more serious, it is of extreme importance to realise that not all respiratory diseases are infectious and that the most common causes of coughing in horses are most likely not associated with an infectious agent.

Clinical approach to a coughing horse

Should coughing be accompanied by other clinical signs such as lethargy, fever, nasal discharge, inappetance or weight loss, it may be an indication of a respiratory infection and warrants investigation by a veterinarian. A veterinary examination will include a complete physical examination, vital parameters will be evaluated, including listening to the horse’s chest. The duration and timing of the coughing, any recent travelling or management changes, as well as the age, use and breed of the horse may be helpful in directing which diagnostic steps to proceed with. Some of these tests may include blood tests, endoscopy of the upper and lower respiratory tract and thoracic ultrasonography. Based on these findings, further diagnostics such as a transtracheal aspirate, commonly known as a lung wash can also be performed. All of these will supply the veterinarian with more information to enable an accurate diagnosis and treatment plan.

Diagnostic procedures such as ultrasonography and performing a lung wash is vital in most cases of coughing associated with an elevated temperature. Thoracic ultrasonography is useful in evaluating the lung periphery and in cases such as bacterial pneumonia, it can be used to diagnose the disease as well as to monitor response to treatment. The importance of a lung wash should not be underestimated as information obtained from the number and type of cells present within the lung wash is essential in the establishment of infectious versus non infectious diseases. In the cases with bacterial infections, the causative bacteria can be identified and cultured. Antibiotic sensitivity can also be determined.

Some examples of respiratory conditions and coughing associated with a fever includes:

  1. Bacterial, viral, fungal or interstitial pneumonia
  2. Equine Influenza virus
  3. Equine Herpes virus
  4. Neoplasia

Picture 1: Cytological examination of a lung wash obtained from a coughing horse. Evaluation of these samples, i.e. looking at the type of cells present within the lung wash can help differentiate infectious from non-infectious conditions. Obtaining samples from the lungs is relatively easy and non-invasive.

 

Picture 2: Ultrasonography of the lungs can provide the veterinarian with much more information regarding the severity of disease. Not all coughing horses with an elevated temperature will have ultrasonographic changes. This picture illustrates the accumulation of fluid within the chest of a horse presented for an elevated temperature. This horse was not coughing and the diagnosis of respiratory disease was made with ultrasonography.

Coughing without an elevated temperature:

Besides viral and bacterial causes, two other common inflammatory conditions can result in coughing.

Recurrent airway obstruction (RAO) or ‘heaves’ is a common cause of coughing in older horses. It is caused by an allergic reaction in the horse’s lungs to dust in the hay, bedding or environment. The allergic reaction results in increased inflammation in the lower airways, with increased mucous production and reduced airway diameter predisposing the horse to coughing. Other clinical signs may include exercise intolerance, increased respiratory rate and effort, with flared nostrils. This condition is non-transmittable between horses and a lung wash is essential in making an accurate diagnosis. (See video via video link below and attached pictures 3, 4 and 5).

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Video: A coughing horse with severe respiratory distress. Most likely diagnosis based on first impressions involved an infectious component. However, following appropriate diagnostic steps, an accurate diagnosis was made and the horse was started on the necessary treatment. This was a non-infectious condition treated with corticosteroids and bronchodilators.

Picture 3 and 4: Same coughing horse with severe respiratory disease.

Picture 5: The same horse a few weeks after corrective treatment.

Inflammatory airway disease (IAD) is a condition most often associated with intermittent coughing, exercise intolerance and increased mucous production. Unlike RAO, these horses usually do not experience airway obstruction, nor do they display excessive efforts to breathe. Mucous also tends to accumulate in the trachea. This is a common form of respiratory disease in young racehorses. An increased number of inflammatory cells are present within the lung washes.

Both these inflammatory conditions are associated with increased mucous production however, the mechanism of disease does not require these horses to be treated with antibiotics. Target specific treatments such as corticosteroids and bronchodilators and most importantly, changing the environment by reducing exposure to dust particles are far more effective ways of treating these conditions.

Other causes of coughing not associated with an elevated temperature:

Post exercise

Exercise induced pulmonary haemorrhage (EIPH)- This condition is most commonly seen in racehorses, following strenuous exercise. Horses in disciplines such as eventing and polo may also suffer from EIPH.

Picture 6: Lung Wash obtained from a horse with exercise induced pulmonary haemorrhage. Only a small number of horses will show signs of epistaxis (bleeding from the nostrils) and additional procedures such as endoscopy of the lower airways or a lung wash is needed to confirm diagnosis.

Post feeding: 

Conditions such as dorsal displacement of the soft palate, soft palate paresis and dysphagia (inability to swallow normally) may lead to coughing post exercise.

Lungworm:

This is another condition leading to coughing not associated with an elevated temperature. This is mostly seen in horses pastured with donkeys.

If no abnormalities are detected upon clinical examination, does it mean that there is no need for concern?

In short, the answer is NO. Many of the conditions associated with coughing without an elevated temperature may not present with any other clinical signs or abnormal lung sounds. This is why further investigation such as endoscopy is advised. Additional diagnostic tests may then follow for an accurate diagnosis to be made.

In conclusion

Not all coughing episodes are associated with an infectious component, but if left untreated, may lead to secondary infections within the respiratory tract. Any degree of inflammation, whether it is associated with acute or chronic conditions, may lead to hypersensitivity and coughing. A thorough investigation is needed due to the number of conditions associated with coughing. Allowing your veterinarian to perform the necessary procedures and make an accurate diagnosis is essential, as it will eliminate the unnecessary use of antibiotics in cases of airway inflammation. Environmental changes are an essential part of the treatment strategy and are as important as actual medical treatment to improve the coughing horse’s quality of life.

 

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