How do horses breathe? What is Equine Asthma and how can we manage it.



How do horses breathe? What is Equine Asthma and how can we manage it.

Like all mammals, horses have evolved a respiratory system to allow for the exchange of oxygen and carbon dioxide between the alveoli, air sacs found deep in the lungs, and the blood capillaries. The graphic above clearly shows this system and how it sits within the equine body. Replenishing oxygen within the body, is a vital process for the developing, maintaining and repairing of the body’s infrastructure of complex cells, tissues and muscles. Horses have outstanding aerobic power and endurance, so have consequently evolved with proportionally large lung capacity.

How do horses breathe? What is Equine Asthma and how can we manage it.

As the above image shows, horses can only breath in and out through their nasal passages, which can cause issues during strenuous exercise. In order to take in enough oxygen, they must synchronise their breathing with every stride. Their delicate alveoli are measured at 1/50,000 of an inch and studies have show that five times as much pressure is exerted on them during strenuous exercise.

What is Equine Asthma?

Many horse owners will have heard of horses suffering from breathing conditions such as having ‘heaves’, being ‘broken winded’ or even suffering Chronic Obstructive Pulmonary disease (COPD). However, it is now recognised that horses suffer from three related respiratory conditions: inflammatory airway disease (IAD), recurrent airway obstruction (RAO), and summer pasture recurrent airway obstruction (SPRAO). The conditions are now commonly termed together as “Equine Asthma”.

Equine asthma, a chronic allergen-mediated inflammatory disease of the lower airways, is found to be highly prevalent in adult horses. Mild-moderate asthma is often found in young, athletic horses and while severe, progressive asthma is found in older horses. The condition has three possible components: airway inflammation, airway hyperresponsiveness and airway remodelling. These components affect and influence the treatment and management of the horse’s condition.

Mild-moderate asthma is likely to effect up to 80% of the athletic horses at some point in their life causing impaired performance. Providing the correct treatment for this can mean that the condition is temporary and prevent the progression to severe asthma.
Severe Asthma is episodic and progressive and must be managed appropriately.

Causes of mild asthma:

An allergen-mediated component is suspected as the cause of asthma in many horses. Alternatively, it could be caused by infection with respiratory viral (EHV-2, equine rhinitis virus A variant) or bacterial (Streptococcus spp) pathogens, or recurrent pulmonary stress associated with strenuous training. It can also be triggered by environmental allergens such as fungal spores found in hay and straw.

Common symptoms include:

  • Coughing (may only be when exercised or after feeding)
  • Noisy breathing (wheezing)
  • Fast breathing rate (look at the flank and see how many times in a minute your horse breaths, should be between 8-20)
  • Using abdominal muscles to assist breathing (flank markedly moves in and out with breathing)
  • Nostrils flaring.

Diagnosis and Treatments:

Primarily these cases should be referred to your veterinary surgeon who will be looking to identify the presence of lower airway inflammation. Severe episodes should be treated as an emergency.

Initially your vets will assess any clinical signs and history as discussed with the owner and from their records. They may well be able to make a presumptive diagnosis in more severe cases. However, to obtain a definitive diagnosis the one or more of the following tests are essential.

  • Bronchoalveolar lavage
  • Endoscopy and Tracheal Wash
  • Response to therapeutic trial.

Once diagnosed, your veterinary surgeon will devise a treatment strategy to alleviate the presenting symptoms based around either short or long term medications such as:

Bronchodilators – these open up the airways which become narrower with the disease. This allows more air to get in and out of the lungs. The drug mostly used is called clenbuterol.

Steroids – may be considered in more severe cases. These reduce pulmonary inflammation and help prevent the horse’s immune system from over-reacting to allergens, therefore helping them to breathe more easily.

Aerosolized medications – these inhalers are designed specifically for horses but function similarly to human inhalers, allowing efficient, direct delivery of the medication to the lower airways and the lungs.

Alternative Therapies – There are a number of therapies that may benefit an Equine Asthma sufferer such as Saline therapy, anti-histamines

Natural supplements – These can be fed and administered without veterinary prescription and may add to relief of the clinical symptoms: Balsamic Air, Mullein, Ventair, Boswelia, Spirulina, Flax oil.

On-going environmental management of Equine Asthma is of paramount importance and represent the cornerstone of treatment. Discussing this with your vet and making any necessary management changes will certainly be beneficial to your horse.

References

Vetline Equine, Understanding Equine Lungs through Evolution, available at: https://vetlineequine.com/understanding-equine-lungs-through-evolution/

Oregon Horse Council, Facts about the equine respiratory system, available at: https://www.oregonhorsecouncil.com/facts-about-the-equine-respiratory-system/

Vetline Equine, Understanding Equine Lungs through Evolution, available at: https://vetlineequine.com/understanding-equine-lungs-through-evolution/

Kara M. Lascola, DVM, MS, DACVIM, Auburn University College of Veterinary Medicine, available at: https://www.msdvetmanual.com/respiratory-system/respiratory-diseases-of-horses/asthma-in-horses

Horse Health Programme, Available at: https://www.horsehealthprogramme.co.uk/coughing-and-equine-asthma/#:~:text=Equine%20asthma%20a%20non%2Dinfectious,as%20heaves%20or%20broken%20wind.