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RAO D I AGNOS I S
Recurrent airway
obstruction
(RAO)
Jane King BVetMed MRCVS,
Westmorland Veterinary Group
What causes RAO?
Heaves or RAO is caused by an allergic
reaction to dust, moulds, fungal spores and
bacteria in the lung of the horse. The airways
or bronchii and bronchioles in the lung are
lined by cells which produce mucus in
response to exposure to these allergens.
These lining cells are surrounded by a collar
of smooth muscle. Affected horses have an
inflammation of these airways characterised
by constriction of this smooth muscle causing
a narrowing of the airways along with
overproduction of mucus and secretions.
In long term (chronic) cases the lining of the
airways becomes thickened and inflamed
further obstructing air flow through the lung.
What are the signs
of RAO?
The narrowed airways in horses with heaves
mean it is harder work for the horses to
breathe normally, these horses breathe harder
and faster than normal. They may have a
‘heaves line’ running along their belly from
all this increased respiratory effort. The extra
mucus production and narrowed airways
often cause the horse to have a cough.
Because this mucus is thick and sticky it often
accumulates in the base of the trachea or
windpipe, when the horse starts to exercise
this may be coughed up. Sometimes these
deposits of thick yellow phlegm may be
coughed up over the stable door.
Occasionally the horse may have a slight
nasal discharge. Unlike infectious causes of
a cough the horse is usually well and with
a good appetite. Milder cases may present
with poor performance as the signs may
only become apparent during hard work.
Veterinary Surgeon
Jane King
XLVets Equine Practice
Westmorland
Veterinary Group
Recurrent airway obstruction (RAO) is a condition that has been known
to affect horses for as long as horses have been domesticated. Over the
centuries, RAO has been given a number of names including broken
wind, heaves and more recently chronic obstructive pulmonary disease
or COPD. It is a common condition and can seriously compromise an
affected animal’s health and ability to work. Any type of horse or pony
can suffer from RAO.
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EQUINE MATTERS