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Vet's Corner

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.

Airway Constriction

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 disease.


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 respiratory disease.

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 cause disease.

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 successfully resolved.

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.