How to treat a horse for heaves
By Gabriele A. Landolt,
Diplomate American College of Veterinary Internal Medicine
What is "heaves"?
Heaves is a chronic, noninfectious airway condition of horses that also
is called recurrent airway obstruction, or RAO, and was formerly known
as chronic obstructive pulmonary disease, or COPD. The disease occurs in
horses more than 6 years of age and is the result of an allergic reaction
to inhaled particles. The allergens, such as molds, that cause heaves are
primarily found in hay and straw.
Once inhaled, an allergic reaction causes the small airways in lung tissue
to narrow and become obstructed. A combination of three factors cause the
airway obstruction: inflammation and thickening of the tissue lining the
airways (bronchiolitis), constriction of the smooth muscles that surround
them (bronchospasm), and accumulation of mucous in the airways.
Typically, one of the first clinical signs noted by an owner is an occasional
cough. As the disease progresses, the clinical signs will become more apparent
and include exercise intolerance, an increased respiratory rate, nasal
discharge, wheezing and flaring of the nostrils.
Due to the obstruction of the small airways, a horse with heaves works
harder to pull air into and expel air from the lungs than a healthy horse.
This increased respiratory work forces the horse to use its abdominal muscles
during the late phase of exhalation. Over time, the additional workload
results in the visible enlargement of the abdominal muscles and the formation
of a heave line. With progression of the disease it becomes increasingly
difficult for the affected horse to expel the air from the lungs at the
end of exhalation and the lungs may remain over-inflated, which is called
emphysema. If left untreated, nonreversible damage to the lung tissue may
occur resulting in the permanent loss of lung function.
How can heaves be diagnosed?
In horses with severe heaves, a veterinarian may be able to make a diagnosis
based on the horse's history and clinical signs. However, additional testing
is required in horses that either have mild to moderate disease or that
fail to respond to appropriate therapy.
Veterinarians evaluate the severity of the disease based on the presence
and types of inflammatory cells in the airway secretions. The examination
of fluid samples obtained from the lungs by bronchoalveolar lavage, or
BAL, is often the most useful testing procedure for making a diagnosis
Fluid samples from the windpipe may also be used, but these samples have
to be interpreted with care. The secretions collected for this test represent
a nonhomogenous sample of cells and debris that accumulate in the lower
windpipe. Because these secretions may have originated from anywhere in
the lower airways, these samples are not representative of any one segment
of the airway.
In contrast, a BAL samples cells and secretions directly from the small
airways, the affected part of the respiratory tract. Because of the differences
in sampling location between tracheal aspirates and BAL, their cytological
interpretations are not interchangeable.
Blood work, such as a complete blood count and blood biochemistry analysis,
and chest X-rays are often of little value in confirming the diagnosis
of heaves. Yet, these tests may be beneficial in ruling out other causes
of respiratory disease, such as pneumonia, pleuritis and neoplasms of the
Is there a treatment for heaves?
While there is no cure for heaves, elimination of the allergens from the
affected horse's environment often reduces or even resolves the clinical
signs. The most important sources for these inciting agents are hay - particularly
round bale hay - and bedding, such as straw.
Horses with heaves ideally should be at pasture with fresh grass as the
source of roughage, supplemented with pelleted feed. If horses must be
stalled they should be maintained in a clean, controlled environment and
fed a dust-free diet (for instance, a complete pelleted feed) to minimize
dust exposure. Although a common practice, soaking the hay in water prior
to feeding is often not sufficient to control clinical signs in highly
Decreasing dust exposure does not only encompass eliminating hay and straw
from the horse's stall, but also requires the careful evaluation of the
animal's environment, stable management practices, and stable design and
ventilation. While horses with heaves are not allergic to outdoor dust,
for example road dust, their airways are hyperreactive to nonspecific stimuli.
Therefore, horses with airway inflammation should not be kept near a dry,
dusty road or paddock.
When horses suffering from heaves have respiratory difficulties, medical
treatment is required. However, it is pivotal to recognize that drug administration
without minimizing environmental allergen exposure will not provide prolonged
The mainstay for medical treatment of heaves is the administration of anti-inflammatory
medicines, such as corticosteroids and bronchodilators. Traditionally,
these drugs have been administered either by mouth or by injection. More
recently, however, aerosolized corticosteroids and bronchodilators administered
through special devices have also become available for the treatment of
heaves in horses. Despite the fact that these aerosolized drug preparations
are more expensive than the oral or injectable formulation, the inhaled
drugs are highly effective and carry a lesser risk of adverse effects.
Long term, the course of the disease depends largely on the effort that
is put into improving the air quality of the environment in which the horse
is kept. While there is no permanent cure of the disease, complete or near
complete recovery from the clinical signs may be achieved with appropriate
Dr. Gabriele Landolt is an assistant professor of Equine Medicine at Colorado
State University's James L. Voss Veterinary Teaching Hospital, specializing
in infectious disease, endocrine disease and health problems in neonates.
In addition to providing care and treatment for equine patients, Landolt's
research focuses on infectious respiratory pathogens such as equine influenza.
She can be reached at the hospital by calling 297-4471.