Equine Respiratory Disease
Respiratory disease prevents horses from being able to perform at their
best. Many horses are frequently not visibly ill, but with respiratory
disease their ability to work can certainly be impaired. If appropriate
action is not taken in the course of the disease, then chronic
conditions can develop that may last for months or even years.
Conditions referred to as heaves, equine emphysema, broken wind, chronic
obstructive pulmonary disease, small airway disease, allergic
bronchiolitis or bronchitis all come about because of previous
respiratory disease in horses left unchecked or inappropriately
treated. All of the named conditions above are different degrees of the
what is essentially the same thing.
In addition in racehorses, many lung bleeders are developed from
previous respiratory disease problems or in horses with ongoing
chronic allergic lung conditions and certainly these horses exhibit
decreased performance levels.
What happens in respiratory disease ?
In the normal horse, not unlike man, breathing supplies oxygen to the
lungs where it enters the blood stream for transfer to the muscles.
Muscles use the oxygen in a process called oxidation which converts
food to energy which is needed to survive and to perform as an athlete.
The lungs are supplied with oxygen through a network of "tubes"
starting at the nostrils, through the pharynx, into the trachea or
windpipe, which divides into bronchi which in turn divide into tiny
little tubules called bronchioles. At the end of the thousands of
bronchioles are the balloon like sacs called alveoli where oxygen is
passed into the bloodstream for transport to all parts of the body.
During exercise, the energy and hence the oxygen requirement greatly
increases and with respiratory disease, the bronchioles become narrowed
or blocked thus reducing oxygen transport.
Three factors of respiratory disease cause this:
a) Mucus in the airways
b) Constriction or narrowing of the airways
c) Inflammation of the airways
In the normal situation, the airways are lined with mucus which traps
particles of dust and pathogens like bacteria and viruses. These
trapped particles are transported out of the lung to the throat and
expelled or swallowed. This process continually cleans the airway and
keeps it open for business.
In respiratory disease mucus increases and becomes thick, sticky and
often mixed with bacterial exudate which is difficult for the body to
move. Buildups occur which physically block the smaller tubules of the
lung, impairing oxygen transport and obviously decreasing performance.
Coughing is an attempt by horses to clear the airways and with mucus
present, productive coughing occurs.
The tubules of the airway contain muscles which can contract and stop
particles from passing deep into the lung. In respiratory disease,
these muscles can become too sensitive and go into what is termed
broncho spasms which narrows tubules too much and decreases the amount
of air and oxygen passing through. As air rushes through these narrowed
bronchioles, it causes a wheezing noise in severely effected horses,
hence the heaves sounds heard in more advanced cases of small airway
With respiratory disease, the airways themselves become inflamed, red
and sore with invasions of bacteria, viruses or allergens. As this
increases, the bronchioles are narrowed, again restricting airflow.
Inflammation without mucus causes a dry non-productive type of cough
because of the constant irritation of the airways.
Signs Of Respiratory Disease
In many respiratory conditions, all three of the above named factors
can occur simultaneously and obviously, this leads to a vicious
cycle of events.
With inflammation, constriction and mucus present in the small tubules
at the same time, many bronchioles become completely blocked and unable
to perform in supplying oxygen to the body.
Signs include the following:
1) Temperature = Frequently increased with acute viral and/or bacterial
conditions. As the disease progresses, temperatures are often normal.
2) Breathing = Fit horses breath slowly at 8-16 times/minute. Horses
with disease often breath faster, shorter or more labored.
3) Coughing = Fit horses rarely cough so coughing can be a sign of
trouble. Dry non-productive coughs usually occur with
more of a chronic condition while productive wet type
coughs are heard more frequently with acute viral or bacterial conditions.
4) Nasal Discharge = Discolored mucus, runny or dirty noses are often
seen both with acute and chronic conditions.
5) Mucus = Strands of mucus on the stall walls or floor are seen with
6) Wheezing = Often heard in chronic allergic type cases or in horses
stabled in dusty barns
7) Heave Line = Seen only in chronic cases with allergic bronchiolitis
or small airway disease or chronic obstructive pulmonary disease.
Causes Of Respiratory Disease
a) Viruses = The most common and often insidious cause of respiratory
disease today. Regular vaccination programs do help but
there are many changing strains of viruses in recent years.
b) Bacteria = Bacteria can cause an acute primary problem in horses
which can often be life threatening, but more likely is
a secondary bacterial condition following a viral attack.
c) Dust/Allergy = One of the main causes of any allergic lung condition
with horses. Hay, straw, feed, grooming or stable dust
from the floor or roof can overload the airway with
debris and with repeated exposure, can readily cause
allergic bronchitis in horses which is the forerunner
to more advanced stages ultimately leading to heaves
some time down the road.
d) Fugal Spores/Allergy = Fungal spores found in hay, straw or feed can
also readily lead to allergic respiratory
disease in horses. Large doses inhaled cause
acute equine emphysema type of attacks.
e) Parasites = Lung worm infection is not common to the Maritimes but
can occur especially in horses grazing with donkeys.
Treatment - Drugs
Treatment of respiratory disease can be divided into two distinct
segments especially with chronic allergic type of conditions.
Drug therapy is often necessary in acute stages of a problem and also
with a chronic condition to apply symptomatic treatments.
a) Antibiotics = Often necessary with bacterial problems or can be
used as a prophylactic against a secondary bacterial
problem when a severe viral condition exists.
b) Broncho dilators = Drugs like Ventipulmin to reopen the airways and
reduce the occurrence of broncho spasms are needed
in both acute and chronic situations.
c) Mucolytics = Drugs like Sputolysin which help liquify and break up
mucus so it can be expelled easier by the horse.
d) Anti-inflammatory/Steroids = Drugs like Prednisone used to help
relieve inflammation and broncho constriction.
e) Diuretics = Drugs like Lasix for relief of pulmonary edema
f) Immunostimulators = Levasole + Equimune are some of the drugs which
fall into this category and supposedly assist
the body's immune system especially with chronic cases.
g) Miscellaneous = Includes drugs like Cromolyn which inhibits mast
cells in the lungs from producing mucus and other
secretions. Used primarily as a prophylactic agent.
Treatment - Environmental Management
The importance of environmental management not only in the prescence
of respiratory disease, but also in the daily management of horses
can not be over emphasized.
Many respiratory conditions are caused by poor stabling environments.
Many chronic lung conditions are caused by poor environments.
Many non-responsive conditions or relapses are provoked and prolonged
by poor environments.
Management and successful control of environment involves maintaining
the horse's level of exposure to causative agents below that which
Every drug listed above can be used to correct or symptomatically treat
various lung conditions, but without continued support from the horse's
environment, the disease condition will prevail.
a) Ventilation = Well ventilated stables help minimize the horse's
exposure to a wide range of environmental contaminants.
Ventilation will help to overcome condensation, prevent molding of bedding material
and minimize the levels of all airborne contaminants to which the horse may be exposed.
b) Stabling = Keeping stables properly cleaned including ceilings and
rafters minimizes dust particles and fungi development.
Hay and straw stored in clean well ventilated areas also
helps and simple things like watering the floor when
sweeping will do wonders for stable dust levels.
ca) Bedding = Even the cleanest of straws contain many dust and fungal
spores so straw should not be used when allergies are a
problem and alternatives like shavings, sawdust, peat moss
and shredded paper can be considered.
*Never bed the stall with the horse inside. Allow any dust
to settle before stabling your horse.
d) Ammonia Control = **Ammonia from a horse's urine is one of the most
noxious and irritating substances to the lungs in a horse's
environment. Prolonged exposure for many hours during the
day and night can cause irritation to the sensitive
airways and can prolong or cause relapses of disease situations.
Clean stalls at least once EVERY day and lime or some of
the new less caustic drying agents should be used on the urine areas.
Recent research indicates ammonia is a leading cause of long term damage to a horse's lungs.
e) Feed = Hay is the single most common source of fungal spores for
horses. Improperly stored feeds are another source for fungi
as well as dust inhalation from poor quality feeds.
In allergic respiratory disease, hay fed should be thoroughly
soaked with water before introduction to the horse or
alternatively, hay cubes or pellets or silage/hayage can be used.
All horses should be fed close to floor level allowing the
horses neck to slope downwards. This helps mucus drain and
lessens the inhalation of dust particles and fungal spores.
f) Grooming = Properly and regularly groomed horses lessen the amount
of dust and dirt carried by the horse himself. As well
stable blankets, sheets,etc. should be regularly cleaned.
g) Outdoors = Keeping horses outside will reduce the challenge of a
dusty environment and if this is practical for your
situation, then all they need is a good shelter from the weather.
While the prevention of the onset of many respiratory diseases is
almost impossible, stable management and the use of proper therapeutic
drugs can ensure that respiratory conditions are short lived and
Attention to air quality will decrease the incidence of respiratory
problems in all horses. Where respiratory disease already exists,
attention to air quality will decrease the duration and severity of
such episodes and will help prevent development of chronic situations.
All of this will lead to a much healthier life for your horse and will
maximize the athletic performance capabilities of your horse.