Recurrent Airway Obstruction (RAO) is a chronic respiratory condition in horses characterized by airway inflammation, bronchoconstriction, and mucus accumulation. It is often triggered by exposure to environmental allergens such as dust, mold, and pollen. Horses with RAO exhibit symptoms including coughing, nasal discharge, and labored breathing, particularly during exercise or in dusty environments. The condition is comparable to asthma in humans and can significantly impact a horse's respiratory function and performance. This page compiles peer-reviewed research studies and scholarly articles that explore the pathophysiology, diagnosis, management, and treatment of Recurrent Airway Obstruction in equine populations.
Gray PR, Derksen FJ, Robinson NE, Carpenter-Deyo LJ, Johnson HG, Roth RA.Airway obstruction and hyperreactivity are characteristics of human asthma and of "heaves," a naturally occurring respiratory disorder of horses and ponies. To document the role of cyclooxygenase products of arachidonic acid metabolism in the pathogenesis of heaves, we measured plasma and bronchoalveolar lavage (BAL) fluid concentrations of metabolites of thromboxane (TX)A2 and prostaglandins (PG) I2 and D2 in five affected ponies and their age- and gender-matched controls prior to and during acute airway obstruction precipitated by housing the ponies in a barn and exposing them to hay dust. P...
Broadstone RV, Scott JS, Derksen FJ, Robinson NE.The effects of atropine on lung function and airway reactivity in two groups of ponies were measured. Principal ponies had a history of recurrent airway obstruction when housed in a barn and fed hay; control ponies had no history of airway obstruction. Principal and control ponies were paired, and measurements were made when principal ponies were in clinical remission (period A) and during an acute attack of airway obstruction (period B). Atropine did not alter pulmonary resistance (RL), dynamic compliance (Cdyn), or airway responsiveness in either group of ponies at period A or in the control...
Scott JS, Garon H, Broadstone RV, Derksen FJ, Robinson NE.We examined the response of five ponies with recurrent airway obstruction (principals) and five age- and gender-matched controls to the aerosol alpha-adrenergic agonist phenylephrine after blockade with propranolol and atropine. Measurements were made with principal ponies in clinical remission (period A) and during acute airway obstruction (period B). The blockade had no effect on base-line pulmonary mechanics in control ponies during periods A and B or in the principal ponies during period A. However, in the principal ponies during period B, blockade increased dynamic compliance (Cdyn) and d...
Derksen FJ, Robinson NE, Scott JS, Stick JA.Ponies with recurrent airway obstruction (principal ponies) and their controls were given aerosolized Micropolyspora faeni antigen via endotracheal tube during a period when the principal ponies were in disease remission. In both groups of ponies, we performed bronchoalveolar lavage (BAL) and measured pulmonary function at base line, and 5 hours after aerosol administration of 30 ml of 0.9% NaCl solution or 30 ml of 1% w/v particulate M faeni antigen in 0.9% NaCl solution. In both groups of ponies, aerosolized M faeni antigen increased WBC count, neutrophil numbers, and albumin concentration i...
Scott JS, Broadstone RV, Derksen FJ, Robinson NE.Ponies with recurrent airway obstruction have hyperresponsive airways during acute disease exacerbations but not during clinical remission. We examined the effect of beta-adrenergic blockade with propranolol on airway responsiveness to aerosol histamine in six ponies with recurrent airway obstruction and six age- and gender-matched controls. Measurements were made with principal ponies in clinical remission (period A) and during an acute period of airway obstruction (period B). beta-Adrenergic blockade did not change airway responsiveness, dynamic compliance (Cdyn), or pulmonary resistance (RL...
Breuer D.In spite of regular vaccinations against equine influenza we are still observing a high rate of patients with respiratory problems in the equine practice. In our practice in Munich Riem, into which a horse clinic has been integrated, 4000 horses have been treated in 1985 alone. 874 of these showed some form of respiratory disease (= 22%). All of the 4000 horses have only been treated curatively, i.e. preventive forms of treatment such as vaccinations, deworming and examinations for insurance companies and prior to selling have not been taken into account. From 1983 until today in our clinic 25...
Armstrong PJ, Derksen FJ, Slocombe RF, Robinson NE.We measured lung function and airway reactivity in response to methacholine and citric acid administered by aerosol in 2 groups of ponies (principal and control). Principal ponies had a history of heaves, a disease characterized by recurrent airway obstruction. Control ponies had no history of respiratory disease. Both principal and control ponies were paired (principal and control), and measurements were made when principal ponies were in clinical remission (Period A), following barn exposure when principal ponies had acute airway obstruction (Period B), and 1 and 2 wk after they were returne...
Derksen FJ, Scott JS, Miller DC, Slocombe RF, Robinson NE.We performed bronchoalveolar lavage (BAL) in 2 groups of ponies. Principal ponies had a history of heaves, a disease characterized by recurrent airway obstruction and airway hyperreactivity when ponies are housed in a barn and fed hay; control ponies had no history of airway obstruction. Ponies were paired (principal and control), and BAL was performed after 2 months of being pastured when principal ponies were in clinical remission (Period A), after barn housing when principal ponies had acute airway obstruction (Period B), and after a 1- and a 2-wk recovery phase of pasture grazing (Periods ...
Derksen FJ, Scott D, Robinson NE, Slocombe RF, Armstrong PJ.Pulmonary function and airway reactivity to IV histamine were measured in a group of ponies with a history of recurrent airway obstruction (heaves) and their age-, weight-, and gender-matched controls. Ponies were studied during a period of clinical remission (period A), after exposure to a barn environment (period B), and twice during a 2-week recovery phase (periods C and D). At periods A, C, and D, PaO2, dynamic compliance (Cdyn), pulmonary resistance, tidal volume, respiratory frequency, and the log dose of histamine required to reduce Cdyn to 65% of base-line value (log ED65Cdyn) of princ...
Derksen FJ, Robinson NE, Armstrong PJ, Stick JA, Slocombe RF.We measured lung function and airway reactivity to histamine administered by aerosol in two groups of ponies. Principal ponies had a history of heaves, a disease characterized by recurrent airway obstruction when ponies are housed in a barn and fed hay; control ponies had no history of airway obstruction. Ponies were paired (principal and control) and measurements were made when principal ponies were at pasture and in clinical remission (period A), following barn housing when principal ponies had acute airway obstruction (period B), and after a further 1 and 2 wk at pasture (periods C and D). ...
Volland-Francqueville M, Sabbah A.When medical history and clinical examination for a recurrent or chronic cough reveal the presence of perennial allergy, the practitioner would be advised to look for mites present in the horse's environment. He can propose this service to his clients.
Wilson DV, Berney CE, Peroni DL, Mullineaux DR, Robinson NE.Acupuncture may be recommended for horses with 'heaves' because it is being increasingly applied to treat human asthma. Therefore, its efficacy was investigated in horses with this asthma-like disease. Objective: To evaluate the efficacy of a single acupuncture treatment for the relief of airway obstruction in heaves-affected horses. Methods: The efficacy of a single acupuncture treatment was tested in 10 heaves-affected horses, and the effect of removal from the dusty stall environment in 5 heaves-affected horses. Before treatment, horses were stabled to induce airway obstruction and, apart f...
Goncarovs KO, Miskovic Feutz M, Perez-Moreno C, Couetil LL.One proposed nonmedical therapy for recurrent airway obstruction (RAO) in horses is a handheld acoustic device that propels sound waves from the nose down the tracheobronchial tree where it is intended to dislodge mucous and relax bronchospasm, permitting clearance of mucoid secretions. Objective: To evaluate the effectiveness and safety of this device when used as per the manufacturer's recommendations as a treatment for RAO. Methods: Nine adult horses previously diagnosed with RAO. Methods: Prospective, cross-over clinical trial. Horses were exposed to a dusty environment until airway obstru...
Herholz C, Straub R, Lüthi S, Imhof A, Busato A.Although pulmonary function tests have been used to evaluate horses with clinically normal lungs and those with recurrent airway obstruction (RAO), comprehensive studies of equine respiratory function, considering factors such as sex, age and usage are not available. Studies on the influence of these factors on pulmonary function in healthy horses are required for interpretation of measurements made in those with respiratory disease. The study was performed with 63 warmblood horses and the status of their pulmonary health was evaluated by clinical examination. The functional aspect of pulmonar...
Gehlen H, Bubeck K, Rohn K, Stadler P.The aim of this study was to investigate the potential haemodynamic effects of valvular insufficiency and recurrent airway obstruction (RAO) in horses with atrial fibrillation (AF). Therefore in ten healthy horses (group 1) and 40 horses with AF a clinical examination, a lung examination, echocardiography and right heart catheterization for measurement of intracardic and pulmonary pressures were performed. According to the clinical findings the horses with AF were subdivided into 4 groups (group 2: AF; group 3: AF/valvular insufficiency; group 4: AF/RAO; group 5: AF/valvular insufficiency/RAO)...
Breuer D.In spite of regular vaccinations against equine influenza we are still observing a high rate of patients with respiratory problems in the equine practice. In our practice in Munich Riem, into which a horse clinic has been integrated, 4000 horses have been treated in 1985 alone. 874 of these showed some form of respiratory disease (= 22%). All of the 4000 horses have only been treated curatively, i.e. preventive forms of treatment such as vaccinations, deworming and examinations for insurance companies and prior to selling have not been taken into account. From 1983 until today in our clinic 25...
Polikepahad S, Haque M, Francis J, Moore RM, Venugopal CS.The purpose of the study was to determine and compare the expression of endothelin (ET) receptors in the peripheral lungs of healthy horses and those affected with recurrent airway obstruction (RAO) using reverse transcriptase polymerase chain reaction (RT-PCR), real-time PCR, Western blot analysis, and immunohistochemical techniques. Two groups of horses (7 healthy and 7 RAO-affected) were selected from a pool of horses destined for euthanasia. The grouping of horses was based on the history, clinical scoring, and pulmonary function testing. After euthanasia, gross postmortem evaluation of th...
Jean D, Vrins A, Lavoie JP.It has been suggested that rapid administration of isotonic saline solution relieves airway obstruction in heaves-affected horses, but the efficacy and tolerability of this treatment is poorly documented. Objective: To determine the respiratory and metabolic effects of a rapid administration of isotonic saline solution in control horses and those with heaves. Methods: Thirty litres isotonic saline solution were administered i.v. to 5 control (Group C) and 9 heaves-affected horses (Group H). Pulmonary function testing and arterial blood gas analysis were performed prior to saline infusion, at 9...
Camargo FC, Robinson NE, Dirikolu L, Berney C, Eberhart S, Derksen FJ, Lehner AF, May J, Hughes C, Tobin T.Trimetoquinol (TMQ) is a very potent and fast acting bronchodilator in horses with heaves. This study assessed the plasma and urinary concentrations of TMQ in horses with heaves following administration via the intravenous (IV, 0.2 microg/kg) and intra-tracheal (IT, 2 microg/kg) routes. TMQ was administered to six horses affected with heaves (RAO - Recurrent Airway Obstruction, used interchangeably) by the above routes and plasma and urine samples collected and stored at -20 degrees C until analyzed. Solid Phase Extraction (SPE) of TMQ was followed by highly sensitive ESI(+)-LC-MS-MS (ElectroS...
Tesfaigzi Y.Exposure of airways to environmental toxins or allergens induces proliferation of epithelial cells. Depending on the type of exposure, existing and newly formed cells can differentiate into mucus-producing cells resulting in mucous cell metaplasia (MCM). During recovery, the epithelium reduces the number of epithelial cells to return to the original state. Understanding the mechanisms involved in this resolution could be useful in deleting mucous cells and, thereby, mucous secretions. We have found that metaplastic mucous cells induced by exposure to ozone, endotoxin, cigarette smoke or allerg...
Derksen FJ, Robinson NE, Berney CE.The dose of aerosol pirbuterol that could be administered safely to ponies (weight approximately 200 kg) was determined by observation for sweating, trembling and excitement and measurement of heart and respiratory rates during cumulative administration of the drug. Sweating, trembling and excitement were first observed following a dose of 2,400 micrograms and became more severe at 3,200 micrograms. These effects were accompanied by an increase in heart rate but not a change in respiratory rate. When 3200 micrograms was administered without prior administration of lower doses, side effects wer...
Scott JS, Berney CE, Derksen FJ, Robinson NE.Pulmonary function measurements were made in control ponies and in ponies with recurrent obstructive pulmonary disease (principals) during clinical remission and during an attack of acute airway obstruction. The ponies were given beta-adrenergic antagonists and agonists to determine the role of beta receptors in recurrent obstructive pulmonary disease, and to determine the subtypes of beta receptors mediating bronchodilation in ponies. Aerosol administration of the beta antagonists, propranolol (beta 1 and beta 2), atenolol (beta 1), and butoxamine (beta 2) decreased dynamic compliance (Cdyn) ...
Finno CJ, McKenzie E, Valberg SJ, Pagan J.Recurrent exertional rhabdomyolysis (RER) occurs in fit, nervous Thoroughbreds fed high nonstructural carbohydrate (NSC) diets. Clinical signs are diminished by feeding low NSC, high fat diets; however, the mechanism is unclear. Objective: To determine if the glucose, insulin and cortisol response to isocaloric diets varying in fat and NSC availability differ in fit vs. unfit Thoroughbreds with RER. Methods: Four fit (10 weeks treadmill training) RER Thoroughbred mares were exercised and fed 3 isocaloric (121 MJ/day) diets in a 5 day/diet block design. Two high NSC concentrates, sweet feed (SF...
Broadstone RV, Robinson NE, Gray PR, Woods PS, Derksen FJ.The effect of aerosol and intravenous administrations of furosemide was examined in ponies with recurrent obstructive pulmonary disease, commonly called 'heaves'. This recurrent airway disease bears many similarities to human asthma. Six ponies with the disease (principal animals) were studied during clinical remission and during an acute attack of airway obstruction precipitated by stabling and feeding dusty hay. Six control animals were also studied. Furosemide (1.0 mg/kg) or vehicle was administered by aerosol in the first study, and intravenously in a second study. In principal ponies with...
Scott JS, Broadstone RV, Derksen FJ, Robinson NE.Ponies with recurrent airway obstruction have hyperresponsive airways during acute disease exacerbations but not during clinical remission. We examined the effect of beta-adrenergic blockade with propranolol on airway responsiveness to aerosol histamine in six ponies with recurrent airway obstruction and six age- and gender-matched controls. Measurements were made with principal ponies in clinical remission (period A) and during an acute period of airway obstruction (period B). beta-Adrenergic blockade did not change airway responsiveness, dynamic compliance (Cdyn), or pulmonary resistance (RL...
Barakzai SZ, Wells J, Parkin TDH, Cramp P.Unilateral ventriculocordectomy (VeC) is frequently performed, yet objective studies in horses with naturally occurring recurrent laryngeal neuropathy (RLN) are few. Objective: To evaluate respiratory noise and exercising overground endoscopy in horses with grade B and C laryngeal function, before and after unilateral laser VeC. Methods: Prospective study in clinically affected client-owned horses. Methods: Exercising endoscopy was performed and concurrent respiratory noise was recorded. A left-sided laser VeC was performed under standing sedation. Owners were asked to present the horse for re...
