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11
EQUINE MATTERS
RESP I RATORY NOI SE
Veterinary Surgeon
Liz Brown
XLVets Equine Practice
Wright & Morten
Veterinary Surgeons
Some horses make respiratory noise when exercised. This can range from a
snort right through to a whistle. These noises are caused by turbulent airflow in
the upper airway. Some noises such as snorting or high blowing have no
deleterious effect on the performance of the horse. Others need further
investigation and treatment as they may impair the function of the airway
and can have a serious effect on the performance of your horse.
What’s that noise?
Guide to respiratory noises
Liz Brown BSc BVSc MRCVS,
Wright & Morten Veterinary Surgeons
Airway structure
When your horse breathes in, air entering
through his nostrils passes along the nasal
passages and over the soft palate, a flexible
flap of tissue that forms the floor of the
pharynx (throat) and keeps the mouth closed
off from the airway. (Unlike you, your horse
can't breathe through his mouth.) The air
then crosses the pharynx and enters the
trachea (or 'windpipe'), through the larynx
(or 'voice box').
Guarding the entrance to the larynx is a
valve system. Its main parts are the epiglottis,
a triangular flap of tissue stiffened by
cartilage, and the two arytenoid cartilages,
which form an inverted V at the entrance to
the larynx. At rest, the epiglottis lies on the
soft palate (the floor of the pharynx). But
when the horse swallows, his tongue pushes
back, pushing the soft palate up to block the
nasal passages and force the epiglottis over
the opening of the larynx. At the same time,
the arytenoid cartilages draw together to
help seal the airway. Food passes safely
over the seal and into the oesophagus.
Initial investigation involves a full clinical
examination, including visual assessment
of the face and sinuses (looking for any
asymmetry), feeling for any scars that may
indicate previous surgery and auscultation of
the airway (listening with the stethoscope).
Further examinations will often include using
a rebreathing bag to attempt to accentuate
respiratory noises by increasing breathing
rate and effort. The horse will also be
examined at exercise.
Some horses only make respiratory noise
when performing a specific action; such as
when they are galloping or when they are
flexed at the poll. The nature of the noise is
assessed and it is determined whether it can
be heard during inspiration (breathing in) or
expiration (breathing out). During cantering
and galloping the horse’s breathing pattern is
linked to the stride pattern with the horse
breathing out when the front legs are on the
ground during each stride.
The next stage is to perform an endoscopic
examination of the upper airway at rest.
This involves passage of a camera into the
nostril and up into the larynx to assess the
airway. Ideally, the exam is performed
without sedation in the first instance in order
to allow a true at rest assessment of the
movement of the arytenoid cartilages of
the larynx (voicebox). If abnormalities are
detected a diagnosis may be reached at
this point.
In some cases the airway obstruction may
only be present during fast work or when the
head is in a specific position and in these
cases the examination at rest may be
completely normal. In these cases an
overland scope is required to remotely
examine the airways during exercise. This
involves an endoscope placed in the horse's
airway and secured to the bridle. A pack
which transmits a signal to a monitor is
secured to the horse's tack or on the rider's
back allowing the larynx to be visualised
while the horse undergoes exercise
(figure 4).
Investigating respiratory noise
Figure 1.
Examination of the respiratory tract