Recurrent Airway Obstruction
Encyclopedia
Recurrent airway obstruction, also known as broken wind, heaves, or sometimes by the term usually used for humans ("chronic obstructive pulmonary disease
" or "disorder"), is a respiratory disease
in horse
s. This is a chronic
condition of horses involving an allergic bronchitis
characterised by wheezing, coughing and laboured breathing.
s, typically dust and mold
spore
s (e.g. Aspergillus
spp.). It is therefore most common in horses fed on hay and bedded on straw. Endotoxin
s from organisms in the bedding and feedstuffs may also play a role.
The condition is most common in the Northern Hemisphere - it is rare in the South.
This is probably because northern horses are more likely to be overwintered in stables or barn, and therefore become sensitised more readily.
In contrast to human asthma
(which it otherwise resembles), RAO is associated primarily with neutrophil mediated inflammation
, and IgE
and mast cells are much less important in the pathophysiology
.
NOTE: A similar condition, Summer Pasture Associated RAO also exists. In this case, the allergens are derived from fodder and pasture. This is more common is summer, and management is reversed: horses should be stabled in well ventilated areas.
, especially in response to strenuous exercise. In some cases (secondarily), the horse may present with acute severe dyspnea, such that it really struggles to inspire sufficient air. This is a veterinary emergency.
In addition, a soft, moist cough may be seen, most commonly in association with exercise or eating. This cough may be productive, with expectoration of thick, viscous sputum.
There may also be an audible wheeze
.
In chronic
cases, a "heave line" may be visible on the ventral abdomen. This is caused by hypertrophy
of the extrinsic respiratory muscles.
If any of these symptoms are observed, veterinary advice should be sought. The veterinarian will usually auscultate (listen to the horse's chest with a stethoscope) to attempt to detect adventitious lung sounds. If these are very quiet, a rebreathing bag may be used - a plastic bag over the nose to intensify the horse's respiratory effort and hence the sounds. This procedure can be dangerous and should not be attempted by non-professionals.
Blood gas analysis may also be carried out, although it is rarely required.
In some cases, a bronchoalveolar lavage
may be carried out - an endoscope is used to look down the trachea
, and mucus and cells are washed out of the lower airways for analysis. Typically, a BAL recovers an abnormally high percentage of neutrophils from an RAO horse - up to 50 or 70% in severe cases.
If this is not practical, certain alterations to stable routine may be effective. The aim is to minimise dust and maximise air quality in the stable. This may be achieved by soaking hay or feeding a dust-free alternative (such as haylage). The length of time to soak hay for the maximum benefit is debated; however, approximately 30 minutes appears to be the current consensus.
Feeding from the ground is often thought to be more beneficial than in a hay net, as this allows any mucus to drain out of the lungs. Those horses that must continue to be stabled are normally bedded on paper, or a combination of rubber matting and paper. Straw and wood shavings contain dust and may irritate the condition further, although some modern "low dust" shavings are thought to be better than straw.
Despite management changes, pharmacological intervention is often required, and almost invariably in severe cases. This breaks down into a number of categories:
1) Bronchodilators:
Often, bronchodilators are the mainstay of therapy. One of the most common is clenbuterol
, either as an oral medication administered twice daily in feed, or via the intravenous route.
Alternatively, aerosol
ised drugs, such as salbutamol
or clenbuterol, may be used. Clenbuterol also has anti-inflammatory actions, and is therefore often preferred.
Other bronchodilators that may be used include aminophylline
, although this may lead to excitation, and is only effective in 50% of cases, or ipratropium
(which is relatively short acting at 4–6 hours duration).
In an emergency, intravenous clenbuterol or atropine
may be used, but care must be exercised with atropine, as it may predispose to adverse systemic side effects such as mydriasis
, excitement, GI stasis and colic
.
2) Corticosteroids:
Oral steroids such as prednisolone
are commonly used; however, side effects are common, and the horse may be predisposed to laminitis
. Therefore, the use of aerosol
ised steroids via an equine inhaler are becoming more common. This route of administration reduces the dose required, and the risk of side effects. Originally, beclomethasone was used, but newer compounds are available now, such as fluticasone propionate
.
3) Mast cell
stabilisers:
Cromoglycate has been used, but this is may or may not be fully effective, as in RAO mast cells have only a peripheral role in the pathophysiology
.
Care should be taken with these drugs in competition horses, as many of them are forbidden substances under racing and FEI
rules.
4) Hay Steamers: A relatively new method of dealing with RAO with horses is to thoroughly Steam the Hay in a commercially available steamer. Feedback from users is very encouraging on the relief factor obtained from RAO. Consistency in feeding horses is important and the hay is just another feed component. A great number of horses suffer from respiratory conditions that is a direct result of the hay they are feeding on. Stored hay contains dust and fungal spores that can cause irritation and inflammation, that can lead to COPD, airway and digestive conditions.
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...
" or "disorder"), is a respiratory disease
Respiratory disease
Respiratory disease is a medical term that encompasses pathological conditions affecting the organs and tissues that make gas exchange possible in higher organisms, and includes conditions of the upper respiratory tract, trachea, bronchi, bronchioles, alveoli, pleura and pleural cavity, and the...
in horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s. This is a chronic
Chronic (medicine)
A chronic disease is a disease or other human health condition that is persistent or long-lasting in nature. The term chronic is usually applied when the course of the disease lasts for more than three months. Common chronic diseases include asthma, cancer, diabetes and HIV/AIDS.In medicine, the...
condition of horses involving an allergic bronchitis
Bronchitis
Acute bronchitis is an inflammation of the large bronchi in the lungs that is usually caused by viruses or bacteria and may last several days or weeks. Characteristic symptoms include cough, sputum production, and shortness of breath and wheezing related to the obstruction of the inflamed airways...
characterised by wheezing, coughing and laboured breathing.
Causes
An allergic reaction to certain otherwise innocuous substances - allergenAllergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....
s, typically dust and mold
Mold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...
spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s (e.g. Aspergillus
Aspergillus
Aspergillus is a genus consisting of several hundred mold species found in various climates worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli...
spp.). It is therefore most common in horses fed on hay and bedded on straw. Endotoxin
Endotoxin
Endotoxins are toxins associated with some Gram-negative bacteria. An "endotoxin" is a toxin that is a structural molecule of the bacteria that is recognized by the immune system.-Gram negative:...
s from organisms in the bedding and feedstuffs may also play a role.
The condition is most common in the Northern Hemisphere - it is rare in the South.
This is probably because northern horses are more likely to be overwintered in stables or barn, and therefore become sensitised more readily.
In contrast to human asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
(which it otherwise resembles), RAO is associated primarily with neutrophil mediated inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
, and IgE
IGE
IGE was one of the largest services company buying and selling virtual currencies and accounts for MMORPG. During its peak time, it had offices in Los Angeles, China , and headquarters & customer service centre in Hong Kong. IGE was one of the main monopoly in virtual economy services, also known...
and mast cells are much less important in the pathophysiology
Pathophysiology
Pathophysiology is the study of the changes of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from an abnormal syndrome...
.
NOTE: A similar condition, Summer Pasture Associated RAO also exists. In this case, the allergens are derived from fodder and pasture. This is more common is summer, and management is reversed: horses should be stabled in well ventilated areas.
Symptoms
Symptoms include, primarily, increased respiratory effort and dyspneaDyspnea
Dyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...
, especially in response to strenuous exercise. In some cases (secondarily), the horse may present with acute severe dyspnea, such that it really struggles to inspire sufficient air. This is a veterinary emergency.
In addition, a soft, moist cough may be seen, most commonly in association with exercise or eating. This cough may be productive, with expectoration of thick, viscous sputum.
There may also be an audible wheeze
Wheeze
A wheeze is a continuous, coarse, whistling sound produced in the respiratory airways during breathing. For wheezes to occur, some part of the respiratory tree must be narrowed or obstructed, or airflow velocity within the respiratory tree must be heightened...
.
In chronic
Chronic (medicine)
A chronic disease is a disease or other human health condition that is persistent or long-lasting in nature. The term chronic is usually applied when the course of the disease lasts for more than three months. Common chronic diseases include asthma, cancer, diabetes and HIV/AIDS.In medicine, the...
cases, a "heave line" may be visible on the ventral abdomen. This is caused by hypertrophy
Hypertrophy
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It should be distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number...
of the extrinsic respiratory muscles.
If any of these symptoms are observed, veterinary advice should be sought. The veterinarian will usually auscultate (listen to the horse's chest with a stethoscope) to attempt to detect adventitious lung sounds. If these are very quiet, a rebreathing bag may be used - a plastic bag over the nose to intensify the horse's respiratory effort and hence the sounds. This procedure can be dangerous and should not be attempted by non-professionals.
Blood gas analysis may also be carried out, although it is rarely required.
In some cases, a bronchoalveolar lavage
Bronchoalveolar lavage
Bronchoalveolar lavage is a medical procedure in which a bronchoscope is passed through the mouth or nose into the lungs and fluid is squirted into a small part of the lung and then recollected for examination. BAL is typically performed to diagnose lung disease...
may be carried out - an endoscope is used to look down the trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
, and mucus and cells are washed out of the lower airways for analysis. Typically, a BAL recovers an abnormally high percentage of neutrophils from an RAO horse - up to 50 or 70% in severe cases.
First Aid
If a horse is severely dyspnoeic (i.e. really struggling to breathe), the most important measure to take is to REMOVE IT FROM THE STABLE OR BARN into FRESH AIR. This can be a life-saving measure in an acute attack. Seek veterinary advice immediately.Treatment
As RAO is primarily a management condition, primary treatment is managemental. Where possible, the horse should be turned out to pasture. When removed from the allergens in the stable, the symptoms will usually subside, although they will recur if the horse is stabled again at a later date.If this is not practical, certain alterations to stable routine may be effective. The aim is to minimise dust and maximise air quality in the stable. This may be achieved by soaking hay or feeding a dust-free alternative (such as haylage). The length of time to soak hay for the maximum benefit is debated; however, approximately 30 minutes appears to be the current consensus.
Feeding from the ground is often thought to be more beneficial than in a hay net, as this allows any mucus to drain out of the lungs. Those horses that must continue to be stabled are normally bedded on paper, or a combination of rubber matting and paper. Straw and wood shavings contain dust and may irritate the condition further, although some modern "low dust" shavings are thought to be better than straw.
Despite management changes, pharmacological intervention is often required, and almost invariably in severe cases. This breaks down into a number of categories:
1) Bronchodilators:
Often, bronchodilators are the mainstay of therapy. One of the most common is clenbuterol
Clenbuterol
Clenbuterol is a sympathomimetic amine used by sufferers of breathing disorders as a decongestant and bronchodilator. People with chronic breathing disorders such as asthma use this as a bronchodilator to make breathing easier...
, either as an oral medication administered twice daily in feed, or via the intravenous route.
Alternatively, aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
ised drugs, such as salbutamol
Salbutamol
Salbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names....
or clenbuterol, may be used. Clenbuterol also has anti-inflammatory actions, and is therefore often preferred.
Other bronchodilators that may be used include aminophylline
Aminophylline
Aminophylline is a bronchodilator. It is a compound of the bronchodilator theophylline with ethylenediamine in 2:1 ratio. The ethylenediamine improves solubility, and the aminophylline is usually found as a dihydrate-Properties:...
, although this may lead to excitation, and is only effective in 50% of cases, or ipratropium
Ipratropium
Ipratropium bromide is an anticholinergic drug used for the treatment of chronic obstructive pulmonary disease and acute asthma. It blocks the muscarinic acetylcholine receptors in the smooth muscles of the bronchi in the lungs, opening the bronchi...
(which is relatively short acting at 4–6 hours duration).
In an emergency, intravenous clenbuterol or atropine
Atropine
Atropine is a naturally occurring tropane alkaloid extracted from deadly nightshade , Jimson weed , mandrake and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a drug with a wide variety of effects...
may be used, but care must be exercised with atropine, as it may predispose to adverse systemic side effects such as mydriasis
Mydriasis
Mydriasis is a dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day...
, excitement, GI stasis and colic
Horse colic
Colic in horses is defined as abdominal pain, but it is a clinical sign rather than a diagnosis. The term colic can encompass all forms of gastrointestinal conditions which cause pain as well as other causes of abdominal pain not involving the gastrointestinal tract. The most common forms of colic...
.
2) Corticosteroids:
Oral steroids such as prednisolone
Prednisolone
Prednisolone is the active metabolite of prednisone, which is also used as a drug.-Uses:Prednisolone is a corticosteroid drug with predominant glucocorticoid and low mineralocorticoid activity, making it useful for the treatment of a wide range of inflammatory and auto-immune conditions such as...
are commonly used; however, side effects are common, and the horse may be predisposed to laminitis
Laminitis
Laminitis is a disease that affects the feet of ungulates. It is best known in horses and cattle. Symptoms include lameness, and increased temperature in the hooves...
. Therefore, the use of aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
ised steroids via an equine inhaler are becoming more common. This route of administration reduces the dose required, and the risk of side effects. Originally, beclomethasone was used, but newer compounds are available now, such as fluticasone propionate
Fluticasone propionate
Fluticasone propionate is a synthetic corticosteroid derived from fluticasone used to treat asthma and allergic rhinitis . It is also used to treat eosinophilic esophagitis....
.
3) Mast cell
Mast cell
A mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin...
stabilisers:
Cromoglycate has been used, but this is may or may not be fully effective, as in RAO mast cells have only a peripheral role in the pathophysiology
Pathophysiology
Pathophysiology is the study of the changes of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from an abnormal syndrome...
.
Care should be taken with these drugs in competition horses, as many of them are forbidden substances under racing and FEI
International Federation for Equestrian Sports
The Fédération Équestre Internationale or in English, the International Federation for Equestrian Sports, is the international governing body of equestrian sports. It recognizes ten international disciplines...
rules.
4) Hay Steamers: A relatively new method of dealing with RAO with horses is to thoroughly Steam the Hay in a commercially available steamer. Feedback from users is very encouraging on the relief factor obtained from RAO. Consistency in feeding horses is important and the hay is just another feed component. A great number of horses suffer from respiratory conditions that is a direct result of the hay they are feeding on. Stored hay contains dust and fungal spores that can cause irritation and inflammation, that can lead to COPD, airway and digestive conditions.