Did you know your horse could be an asthmatic? Rather than being a recently discovered
syndrome in horses, equine asthma is merely a reclassification of conditions previously
called Inflammatory Airway Disease (IAD) in young horses now called mild equine asthma
and Chronic Obstructive Pulmonary Disease (COPD) or Recurrent Airway Obstruction (RAO)
which has been renamed as severe equine asthma. Both conditions show the same clinical
signs, chronic coughing, mucous production and poor performance, but as the name
suggests, vary by severity. However, it should not be seen as a disease continuum where the
mild condition becomes severe over time as many mild cases recover.
Clinical signs develop from exposure to aerosolized particles in the horses environment.
These particles include fungi, mold, toxins from bacteria, vegetative matter, dust and gases
like ammonia. Inflammation and mucous in the airways impedes airflow and the ability for
oxygen to diffuse across the lining of the lung tissues, the alveoli, to enter the bloodstream.
This leads to poor performance and reduced exercise tolerance. IAD type asthma is
extremely common in racehorses but can be challenging at times to pinpoint as a cause of
poor performance because of its multifactorial nature and it being also difficult to define
objectively. Affected horses usually cough early in exercise, have a decent amount of
tracheal mucous and elevations of neutrophils, eosinophils and mast cells (types of white
blood cell) in lung wash samples. Nasal discharge is not a definite feature of mild asthma.
One main distinctive characteristic of the more severe type of asthma is that affected horses
often experience laboured breathing even at rest.
Treatment of both conditions consists of anti-inflammatory doses of corticosteroids such as
dexamethasone and bronchodilators such as clenbuterol to increase the diameter of small
airways in the lungs. These drugs may be given orally or by injection but can be delivered via
aerosolization in a nebuliser. However, metabolites of drugs given by inhaler will still appear
in the blood and urine so cannot be given close to drug tested competitions. It is important
to realise that bacteria are not a central component of this condition, rather it is a matter of
controlling inflammation. Therefore antibiotics are not required in the vast majority of cases
where the horse is clinically well. Supplementation with omega 3 fatty acids may also
improve clinical signs.
Other aids to managing equine asthma include changing to low dust bedding and feedstuff
and also improving barn ventilation or increasing time spent in the paddock. Immersing hay
in water also reduces exposure to respirable dust by approximately 60%. Allowing horses to
eat their hay from the floor reduces exposure to dust four fold compared to feeding the
same hay from a hay net. Offering a complete pelleted feed is also a good option. Changing
bedding from straw to low-dust cardboard material can cut respirable dust levels in half and
reduce mold concentration to negligible levels. Barn activity such as feeding and mucking
out usually increase dust particles in the air so it may help to keep doors open when there is
a lot of foot traffic around asthma prone horses. And of course the ubiquitous leaf blower
should be avoided when horses are present in the stables.
If you think your horse may be suffering from equine asthma or you have any further questions, please feel free to get in touch with one of our Vets.
Dr Finbar Manning 0438 166 578
Dr Eoin Kelly 0418 978 558
Dr Pieter den Boon 0429 326 700