Coughing horse

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Coughing Horse

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Introduction

The coughing horse can be very frustrating for
the owner and a vet to treat. Coughs in horses are mostly
due to allergic reactions to stable dust and pollen. There
are however many cases of viral infection which also result
in long term irritation and produce coughs that do not
respond easily to veterinary treatment. Use of antibiotics
usually has little effect because the viruses and
micro-organisms that cause the problem are not very
sensitive to these drugs.



Coughing
horses

What is
it?

Cough can be associated
with a number of different conditions, some minor, others
more serious.

Simply coughing is the sudden, noisy expulsion of air from
the lungs allowing mucus and other material to be cleared
from the airways. In horses it is an involuntary reflex,
initiated by sensory cells located in the lining of the
trachea and bronchi. These sensory cells are stimulated by
irritation, hence they are often referred to as irritant
receptors. Once stimulated, these receptors send messages
along nerve pathways to the cough centre in the brain which
controls the muscles of the larynx and diaphragm as well as
the intercostal and abdominal muscles.

Because the horse is an athletic animal, its lungs are
extremely large. The volume of air inhaled with each breath
is in the order of 6 to 8 litres for an adult horse. The
trachea is also a large structure, extending the length of
the neck from the larynx to past the first pair of ribs
where it divides into the left and right bronchi. Lining
the trachea and bronchi (and the smaller lower airways) is
a membrane made up of millions of microscopic mucus
producing cells with hair-like projections called cilia.
This muco-cilliary arrangement means the lining of the
airway is always kept moist by a thin layer of mucus which
is continuously being pushed forwards by the wave-like
motion of the cilia.

Causes

There are numerous causes of irritation and hence reasons
why a horse starts coughing:

• Foreign Objects

Occasionally a foreign body such as a stalky piece of hay
or straw, finds its way into the larynx or trachea. The
horse is usually distressed but the forcefulness of the
cough is usually enough to dislodge the object.

• Viral Infections

This is probably the major cause of coughing in horses.
There are several respiratory viruses that can affect
horses but in New Zealand the most common are the two
members of the Herpes family, known simply as Equine Herpes
1 (EHV1) and Equine Herpes 4 (EHV4). It is important to
note that coughing is not always a feature of EHV
infections, some horses show few outward signs other than a
slight nasal discharge and a loss of appetite.

Other respiratory viruses that can cause coughing include
Rhinovirus and Equine Influenza.

• Bacterial Infections

These often follow a viral infection, in fact the two often
overlap. Bacterial infections are usually associated with a
thick nasal discharge and a productive cough. The infection
may be isolated to the airways, or in more serious cases
the infection may develop into pneumonia with involvement
of the lung tissue. Two serious bacterial respiratory
infections that affect young horses in particular are
Strangles and Rhodococcus Bronchopneumonia.

Bacterial infections can involve the guttural pouches
causing a persistent cough that does not respond to
antibiotic medication.

• Allergies

These are a common cause of coughing in horses. They are
initiated by the inhalation of fungal spores or dust
particles and result in a chronic inflammatory reaction in
the lower airways. The cough is usually chronic due to the
constriction of the small airways.

• Parasites

Lungworm can cause coughing in horses that are kept with
donkeys. The small lungworms live in the lower airways and
are a source of irritation. Lungworms only grow to maturity
and produce eggs when the donkey is their final host, hence
horses with lungworm cannot infect other horses.

Roundworm infections can cause coughing in foals and
weanlings due to the larvae migrating through the lung
tissue as part of their life-cycle.


• Exercise Induced Pulmonary Haemorrhage


Also commonly referred to as “bleeding from the lungs”,
this is a cause of coughing mainly in galloping horses. It
has always been known that chronic lower airway infections
play a significant part in the onset of the problem but new
research now suggests that the transmission of shock waves
from the forelegs through the chest wall and off the
rib-cage onto the lungs during galloping, also plays an
important part. Any horse that starts coughing soon after
intense exercise should be scoped to determine whether they
have blood in their trachea.

• Upper Respiratory Tract
Problems


There are several clinical entities involving abnormal
function of the upper respiratory tract that can cause
coughing. The most common of these are Epiglottic
Entrapment and Laryngeal Hemiplegia, both involving the
larynx. Horses with these problems usually show other signs
besides a cough, in particular abnormal breathing noises
during exercise.



Horses in
the snow

Diagnosis

To enable effective treatment to be carried out, it is
important that the cause of the cough be identified
accurately. This involves a detailed veterinary examination
beginning with an assessment of the horse’s general health.
The presence of other affected horses in the same stable or
paddock maybe significant. Another important fact to
consider at this stage is whether the cough is related to
feeding or to exercise.

Listening to the chest with a stethoscope while the horse
is standing quietly, may reveal abnormal breathing sounds
but these can be difficult to detect using this method.
Examination of the throat, trachea and bronchi is possible
using a flexible fibre-optic endoscope. This is a valuable
aid to diagnosis especially when carried out immediately
after exercise as it allows direct assessment of all these
structures

Another diagnostic test that can be carried out is a
tracheal wash. A fine tube is passed through the endoscope
into the bronchi and between 50 to 100mls of sterile saline
is injected through the tube and allowed to mix with any
fluid and cellular debris in the airways. The mixture is
then drawn back into the tubing and sent away for
laboratory analysis. The presence of bacteria, fungal
spores, red blood cells, or inflammatory cells can be
assessed.

Routine blood tests can be useful to indicate the presence
of infections (white cell count) and inflammation
(fibrinogen) although these indicators are not specific for
the respiratory system.

Treatment

Once a diagnosis has been reached, the appropriate
treatment programme can be started. Treatment can involve
any of three options;

Management,

Medical,

Surgical.



Good management practices that can be carried out routinely
to help avoid coughing related problems include;

Avoid stabling in poorly ventilated stables. Muck out
stables regularly. Ammonia from urine soaked bedding is a
respiratory irritant.

Avoid feeding dusty or mouldy hay. Hay is best soaked for
15 minutes before feeding.

Feed low to the ground to assist natural drainage of the
airways by muco-cilliary clearance.

Vaccinate all horses against EHV1 & EHV4 infections.
Vaccines do not always prevent infections but they
certainly reduce their severity.

Worm regularly, especially young horses and horses grazing
with donkeys.

Keep horses warm after exercise and in cold or wet
conditions.

Care needs to be taken during long float trips as this is
when horses are most susceptible to respiratory infections.
The combined affects of close confinement with other
horses, increased body temperature, poor ventilation and
the head being raised for prolonged periods, are all
significant contributing factors.

There are several products available that can be useful in
helping to treat and in some cases prevent coughs and
colds.

Treatment
and Prevention


Avoid Undue Stress.

Treat the Symptoms.

Maximise Immune Competence.

Minimise the Chance of Re-infection.