Small Airway Disease (SAD) &Chronic Obstructive Pulmonary Disease (COPD)

Small Airway Disease (SAD) &
Chronic Obstructive Pulmonary Disease (COPD)
by Philip J. Johnson, Professor 6 years. These horses are often accommodated This muscle thickening, referred to as a “heave
Equine Internal Medicine
in barns at race or race training facilities. This
line,” occurs as a result of increased abdominal
Veterinary Medical Teaching Hospital
variant of bronchiolitis/COPD is also known as
breathing efforts. However, the absence of a
College of Veterinary Medicine,
infl ammatory airway disease or small airway
heave line should not be used to rule out a
University of Missouri, Columbia, MO 65211
disease (S.A.D.). SAD is believed to be more
diagnosis of COPD.
Email: johnsonpj@missouri.edu
directly related to the effects of immune

Although there are numerous other causes
reaction against various respiratory viruses in
of weight loss and exercise intolerance, COPD is
What is Chronic obstructive pulmonary
the small airways.
generally the most common cause of coughing,
disease (COPD)?
What are the clinical manifestations of COPD?
nasal discharge, and respiratory embarrassment

Chronic obstructive pulmonary disease,

The most common clinical manifestations
in adult horses. COPD is so common that, in
possibly the most common medical condition
of COPD are directly referable to increased
many instances, the signifi cance of signs of
of mature horses, is also known by a number
resistance to air movement through the airway
mild disease (such as intermittent coughing
of other names, each term referring to a
passages as a result of bronchiolitis. In the
or slight nasal discharge) is not properly
different clinical manifestation:
beginning, mildly affected horses exhibit slightly
appreciated. All too often, intermittent coughing
• Heaves
increased respiratory effort and respiratory rate
in barn-accommodated horses is attributed to
• Recurrent
airway
disease
following exercise. As the condition progresses,
an “innocuous” barn cough. In those cases,
• Infl ammatory airway disease
increased respiratory effort will be apparent
recognition and early treatment for COPD would
• Chronic
bronchitis/bronchiolitis
in the standing horse at rest. Horse owners
be more effective than, as often happens,
• Small
airway
disease
often miss these early changes in the exercise
waiting until severe lung damage has occurred
•
Bronchiolar hyperreactive disease
capacity and respiratory character of mildly
(irreversible lung scarring).
• Equine
asthma
affected horses. In time, further clinical signs
What causes COPD?
• Emphysema
include intermittent coughing and a bilateral

COPD is the situation in which the
• Broken
wind
nasal discharge. Severely affected horses may
movement of air to and from the lung is
• Hay
sickness
lose weight. All of these clinical signs are more
obstructed by the effects of bronchiolitis.
•
Summer pasture associated obstructive
prominent at a time when horses are exposed to
Bronchiolitis is infl ammation of the tiny airway
pulmonary disease
aeroantigens in the atmosphere, typically during
passages deep in the lung. Bronchiolitis causes
• Chronic
airway
disease
periods of indoor accommodation. COPD does
obstruction by virtue of four different effects.

COPD is a condition in which infl ammation
not cause a fever – an important point when
•
Bronchoconstriction: The presence of
in the small airways of the lung leads to
differentiating this condition from the infectious
infl ammation in the bronchiole leads to
impaired ventilation of the lung. The airway
respiratory diseases. However, in hot weather,
contraction of the muscle in its wall.
begins at the nostrils and passes down the
the rectal temperature of COPD-affected horses
•
Thickening of the wall of the bronchiole.
windpipe (trachea) into the lungs. The smallest
may indeed be increased because the reduction
•
Production of exudate: The presence of
branches of the windpipe that are very close
in airfl ow through the airways interferes with
infl ammation in the wall of the bronchiole
to the actual blood – gas interface (pulmonary
thermo-regulation and causes reduction in the
leads to increased secretion of thick
alveoli) are known as terminal bronchioles.
ability of the horse to eliminate heat (leading to
airway-blocking exudate that contains

Most commonly, COPD occurs as a
hyperthermia).
infl ammatory cells and mucus (“mucopus”).
consequence of immune-induced infl ammation

The symptoms often become less
•
Fibrosis: In time, the presence of infl am-
in the terminal bronchioles (“bronchiolitis”) of
prominent or inapparent when the horses are
mation in the wall of the bronchiole causes
the horse’s lung. There are several potential
accommodated at pasture. In rare cases, COPD-
structural changes that are relatively
causes for immune-mediated bronchiolitis.
affected horses will be found in a sudden state
permanent and act to permanently
When are signs of COPD recognized?
of severe respiratory distress. Such horses may
interfere with the ability of drugs to cause

In horses, there are two distinct variants of
not have appeared abnormal to the horse owner
lumenal dilatation.
bronchiolitis. COPD is very common in horses
although, on recollection, these horses are

The exudates, like the normal secretions of
aged over 6 to 7 years. In these horses, clinical
commonly reported to have had an occasional
the respiratory tract, are moved up toward the
signs of COPD are directly attributable to
cough. Signs of acute-onset severe respiratory
mouth and swallowed. In COPD, the excessive
exposure to allergenic dust in the environment
distress include increased respiratory rate,
quantity of exudate (mucopus) often appears at
(aeroantigens). Clinical signs of COPD arise
increased respiratory effort (with abdominal
the nostrils and is recognized as a dirty nose or
whenever horses inhale these aeroantigens.
breathing), fl aring of the nostrils, and cyanotic
a nasal discharge (usually from both nostrils).
If the horse is not exposed to aeroantigens,
(blue colored) mucous membranes.
The quantity of mucopus that appears at the
signs of COPD may be completely absent. The

In one exceptional type of COPD, the
nostrils is often increased when the horse
most common aeroantigens include molds
affected horse exhibits respiratory symptoms
grazes grass or eats hay off the ground because
that grow on hay and straw. When horses
when accommodated outside at certain times
the effect of gravity help it to drain down the
begin to develop COPD, the clinical signs
of the year. It is believed that these horses
airways to the nostrils. Coughing occurs because
are usually seasonal in occurrence during
are “allergic” to inhaled pollen (like hay fever
clumps of mucopus act to physically activate
the fi rst few years and may be correlated
in children). This COPD variant is known
cough receptors in the wind pipe as a result of
with the environment in which the horse is
as “summer pasture-associated obstructive
mechanical irritation.
accommodated. As a rule, these mature COPD-
pulmonary disease” or SPAOPD, for short.

At the root cause of COPD, bronchiolitis
affected horses are more likely to develop
For these horses, the clinical expression of
is provoked by an immune-mediated reaction
symptoms when accommodated indoors and
disease occurs in the summer and fall when
against inhaled aeroantigens. Horses are
fed hay, especially when bedded on straw.
they are accommodated at pasture. SPAOPD
exposed to inhaled aeroantigens whenever they
These same horses may become completely
is apparently much more common in the Gulf
eat hay (some hay is worse that other hay, but
asymptomatic when accommodated outside
coast states.
all hay represents a risk), are bedded on straw,
at pasture.

In horses that have been affected with
and are accommodated in barns (especially

The second variant of bronchiolitis occurs
COPD for several years, there sometimes
old barns and in barns in which hay and straw
in younger horses, typically aged between 3 to
develops a line of muscle thickening in the fl ank.
are stored). Horses affected with SPAOPD
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are exposed when they are accommodated
Management adjustments intended to
only the best quality hay which is neither
at pasture in summer. COPD-affected horses
reduce the risk of exposure to inhaled
dusty nor moldy (actually, all hay is
may also exhibit aggravation of signs when
aeroantigens:
moldy to some extent)
exposed to non-allergenic air contamination
•
Hay which has been cut and baled in a wet
(dusty arena, wood shavings, and petrochemical
•
Optimize the weight of affected horses
spring/summer will be particularly bad
pollution) – this exacerbation of signs is related
(which are sometimes too fat)
(in terms of mold content) the next
to the fact that the affected horse’s airway has
•
Fresh (outdoor) air is usually very important
winter/spring
already been sensitized by the presence of
(exception = summer pasture -
•
Barn-dried hay is preferable
infl ammation due to exposure to aeroantigens,
associated COPD)
•
Hay should be soaked under water prior to
however.
•
Avoid all dusty environments
feeding by completely immersing the

Others have suggested that COPD
•
Do not accommodate inside barn unless
hay (eg: in a plastic hay net) for 2 hours
represents a natural continuance of the effects
absolutely necessary
immediately prior to feeding and fed in a
of viral respiratory tract infl ammation as younger
•
Do not feed with any hay unless absolutely
hay net, dripping wet
horses. COPD has also been recognized as a
necessary
•
Exercise in cold weather often aggravates
complication of smoke inhalation (in horses that
•
Allow access to appropriate grazing
the problem and should be avoided
survive barn fi res) and lung worm infections.
•
Avoid excessively dusty paddocks – once
•
Minimize ammonia build-up from wet
It is possible that any provocative factor that
initiated, all dust is aggravating to
bedding/urine pooling and ineffi cient
leads to airway infl ammation could, given the
horses affected with COPD
stall drainage
appropriate circumstances (concomitant mold
•
When necessary, pasture grazing should
•
Although an expense would be involved (but
exposure) lead to a state of immunological
be supplemented with oats, silage,
not as great as might be anticipated),
hypersensitivity in susceptible horses.
haylage, pelleted feed, alfalfa cubes,
special adaptation of a single stall or
etc. HorseHage™ can be used as an
loose box can be undertaken. The stall
How is the diagnosis of COPD established?
alternative roughage source in the diet
would be sealed-off from the common

During physical examination of COPD-
(available from Marksway-Hillandale
air-space of the barn environment and
affected horses, the veterinarian will place
Farm, Pomfret Center, CT). Beet pulp
ventilated through a high effi ciency fi lter
importance on the breath sounds detected
is another useful roughage for these
in association with an air-conditioner.
through the stethoscope (thoracic auscultation).
horses. Other recommended COMPLETE
•
Do not accommodate in close proximity to
Thoracic auscultation should be properly
undertaken in a quiet environment and both
PELLETED RATIONS include Purina
busy or dusty roads
sides of the chest will be examined. Some
Horse Senior and Purina Horse Chow.
•
If hay has to be fed, it should be fed on the
veterinarians also listen to the breath sounds
•
Hay or straw should not be stored in close
ground, not at head level in a hay net.
in the windpipe. Making the horse breath a
proximity to grazing areas – certainly not
in the same air space.
Bottom line
little harder may increase the ease with which
•
Do not feed any other horses in the same

This condition is eminently treatable.
breath sounds can be detected and evaluated.
pasture with hay – COPD horses may be
MOST affected horses benefi t greatly from
This increased work of breathing can be
affected by close proximity to hay and
simple changes to the atmospheric management
accomplished by either having the horse trotted
and do not require to be treated using
for a few minutes or by making the horse
straw.
expensive drugs. MOST affected horses revert
quietly breathe into a bag (re-circulating carbon
•
Do not allow access into the barn
to normal breathing if the underlying causative
dioxide increases the breathing effort). The size
•
Protection from particularly cold weather
aeroantigens can be eliminated. A minority of
of the lung fi eld is often examined by tapping
may be afforded by an open “lean-to”
affected horses have sustained permanent and
on the chest (thoracic percussion) – in COPD,
arrangement or by use of a New Zealand
irreversible changes (scarring, etc) that prevent
the size of the lung fi eld is often increased. It
rug
and impede successful treatment.
is often very easy to elicit a cough from COPD-
•
If indoor accommodation MUST be used, all
affected horses by lightly squeezing the wind-
horses in the communal barn should be
pipe just behind the larynx.
managed under the same precautions
In virtually all horses affected with COPD,
•
Minimize exposure to busy road traffi c
the response to avoidance of aeroantigens
(vehicular exhaust is an aggravating
(without the use of any drugs) is excellent within
factor)
a few days and this response serves to further
•
Straw bedding should be avoided
corroborate the diagnosis of COPD.
•
Preferred bedding materials include peat
What is the treatment for COPD?
moss, paper, clay, wetted-down wood

The treatment for COPD falls into two broad
shavings/saw dust, sand.
categories:
•
Hay or straw MUST NOT BE STORED
•
Changes in management intended to
IN THE SAME AIR SPACE as indoor-
eliminate exposure to inhaled aeroantigens
accommodated horses
(see list at right)
•
Extraction fans are rarely very useful (and
•
Drug strategies intended to promote airway
may even be exacerbative). They should
function
not be used as an “excuse” for proper
The MOST IMPORTANT aspect of treat-
ventilation
ment for COPD is clearly the avoidance of
•
Avoid damp, dusty, poorly ventilated barns
aeroantigens. For most COPD-affected horses,
•
Indoor environment should be routinely kept
a complete recovery from the problem can be
as dust-free as possible
achieved simply by effectively eliminating inhaled
•
Do not undertake cleaning operations when
aeroantigens from the horse’s environment. As
COPD-affected horses are in the same
a rule, without resort to some improvement in
environment (risk of churning up dust)
the management, the drug strategies are rather
•
If hay must be used (ideally it will not), use
SUMMER, 2007




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