Diaphragma et Pulmones
The equine lungs are large (roughly 5–7 kg total, capacity on the order of 40–55 liters) and sit within the thorax, separated from the abdomen by the diaphragm. During quiet breathing the diaphragm is the main inspiratory muscle. At the canter and gallop there is usually a 1:1 locomotor-respiratory coupling, with the horse typically taking one breath per stride. Movement of the abdominal viscera (a proposed "visceral piston"), back flexion and abdominal-muscle contraction have all been suggested to help link breathing to the stride; equine studies disagree on how much the visceral piston contributes. Clinical evaluation includes auscultation (often with a rebreathing bag to increase tidal volume) and endoscopy after exercise to look for exercise-induced pulmonary hemorrhage (EIPH). Respiratory disease anywhere in the system limits the horse’s ability to meet oxygen demand.
EIPH is common in racehorses and detected by post-exercise tracheal endoscopy. Inflammatory airway disease, recurrent airway obstruction, and pneumonia all affect performance. Rebreathing examination helps auscultate deeper lung fields.
Tear in the diaphragm allowing abdominal organs to enter the thorax.
## Overview Recurrent airway obstruction, also called heaves or severe equine asthma, is a chronic allergic airway disease similar to human asthma. Exposure to dust and mold in hay and bedding causes
## Overview Exercise-induced pulmonary hemorrhage (EIPH) is bleeding into the airways and lungs during strenuous exercise. It affects the majority of racehorses and many other horses in high-intensit
## Overview Pneumonia is infection and inflammation of the lung parenchyma (the functional tissue of the lungs). In horses it is not a single disease. Adult horses most often develop bacterial pneumo
## Overview Pleuropneumonia is infection of both the lung and the pleural space. It is a severe form of pneumonia, often called shipping fever because long-distance transport with the head elevated i
Coughing, nasal discharge, labored breathing, or poor performance at speed should be evaluated. Keep dust and ammonia low in the barn to support respiratory health.
Tear in the diaphragm allowing abdominal organs to enter the thorax. Signs include: Respiratory distress; colic; decreased lung sounds on one side; can be acute or chronic
## Overview Recurrent airway obstruction, also called heaves or severe equine asthma, is a chronic allergic airway disease similar to human asthma. Exposure to dust and mold in hay and bedding causes airway inflammation and constriction. Signs include chronic cough, nasal discharge, increased respiratory effort, and in advanced cases a heave line from abdominal muscle hypertrophy. Average age of onset is around 9 years. ## Causes Hypersensitivity to organic dusts, especially in hay. ## Diagnosis Clinical signs, endoscopy, and bronchoalveolar lavage. Response to environmental change supports the diagnosis. ## Treatment Environmental management is essential (pasture turnout, soaked or steamed hay, dust-free bedding). Corticosteroids and bronchodilators control inflammation and spasm. ## Recovery and Prognosis Lifelong but manageable. Clinical signs can be well controlled with strict environmental changes. ## Prevention Minimize dust and mold exposure, especially for susceptible horses. Signs include: chronic cough; nasal discharge; increased respiratory effort; heave line in advanced cases
## Overview Exercise-induced pulmonary hemorrhage (EIPH) is bleeding into the airways and lungs during strenuous exercise. It affects the majority of racehorses and many other horses in high-intensity sports. Visible nosebleeds occur in only a small percentage; most cases are detected by endoscopy. ## Causes Rupture of pulmonary capillaries under the high vascular pressures of intense exercise. ## Diagnosis Endoscopy after exercise showing blood in the trachea, or cytology of bronchoalveolar lavage. ## Treatment Furosemide before exercise reduces severity in many horses. Management of airway inflammation and racing schedules is supportive. Nasal strips may help some horses. ## Recovery and Prognosis Most horses continue to compete. Severe or repeated hemorrhage can affect performance and, rarely, be life-threatening. ## Prevention Furosemide use where permitted, and attention to respiratory health. Signs include: blood at the nostrils after exercise (minority of cases); poor performance; blood seen on post-exercise endoscopy
## Overview Pneumonia is infection and inflammation of the lung parenchyma (the functional tissue of the lungs). In horses it is not a single disease. Adult horses most often develop bacterial pneumonia when organisms that normally live in the upper airway reach the lower lungs and overwhelm local defenses. Viral respiratory infections (especially equine influenza and equine herpesvirus) rarely cause pneumonia by themselves but damage the airway lining and predispose to secondary bacterial infection. Aspiration of feed, saliva, or medication can also produce pneumonia. Long-distance transport with the head elevated (shipping fever) is a well-recognized risk factor that allows bacteria to colonize the lower airways during prolonged transport and can progress to the more serious complication of pleuropneumonia. Foals, particularly those one to five months of age, face a different and often more serious form of pneumonia caused by the intracellular bacterium Rhodococcus equi. This organism produces abscesses in the lungs and can affect other organs. Because the causes, clinical course, diagnostic approach, and treatments differ substantially between adult bacterial pneumonia, viral-associated disease, aspiration pneumonia, shipping-related disease, and Rhodococcus equi pneumonia in foals, management must be tailored to the specific situation. ## Causes In adult horses the most common bacterial isolate from pneumonia is Streptococcus equi subspecies zooepidemicus, a normal inhabitant of the upper airway. Mixed infections that include other aerobic bacteria (such as Escherichia coli, Klebsiella species, Actinobacillus species, and Pasteurella species) and anaerobic bacteria are common, especially in more severe or chronic cases. Viral infections such as equine influenza and equine herpesvirus type 1 or 4 damage the mucociliary clearance mechanism and open the door to these secondary bacterial invaders. Aspiration pneumonia occurs when foreign material enters the lungs. The most frequent triggers are esophageal obstruction (choke), difficulty swallowing due to neurologic disease, improper administration of oral medications or mineral oil, and complications of general anesthesia. Transport-associated pneumonia (shipping fever) develops when horses are hauled long distances, particularly with the head tied in an elevated position. Inability to lower the head impairs normal airway clearance, allowing bacteria to colonize the lower respiratory tract during prolonged transport. This process can progress to pleuropneumonia if infection spreads to the pleural space. In foals one to five months old, Rhodococcus equi is the predominant and most serious cause of pneumonia. The organism is widespread in soil and feces. Foals become infected by inhalation or ingestion in the first weeks of life, but clinical signs usually appear later. Other bacteria can also cause pneumonia in foals, but R. equi is distinctive for its ability to survive inside cells and form large abscesses. ## Diagnosis Your veterinarian begins with a thorough history and physical examination, including careful auscultation of the lungs for abnormal sounds such as crackles or wheezes. Bloodwork often shows elevated white blood cell counts and inflammatory proteins. Thoracic ultrasound is useful for detecting peripheral lung consolidation, abscesses, or pleural fluid. Radiographs can reveal deeper lung patterns, including the nodular abscesses typical of Rhodococcus equi in foals. Lower-airway sampling, especially sterile tracheal or transtracheal aspirates for cytology, culture, and susceptibility testing, is most useful for confirming bacterial infection and guiding therapy in severe or nonresponsive cases. Bronchoalveolar lavage is not an equivalent primary diagnostic for pneumonia. In foals suspected of Rhodococcus equi, polymerase chain reaction testing for the virulence-associated protein A (vapA) gene on airway samples can support etiologic confirmation. Thoracic ultrasound is widely used for screening and monitoring of foals on endemic farms, but it is not a standalone gold standard for confirming R. equi pneumonia. Viral testing (nasopharyngeal swabs for polymerase chain reaction) is appropriate when a viral outbreak is suspected. ## Treatment Treatment depends entirely on the cause and the individual patient. For bacterial pneumonia in adult horses, antimicrobial therapy is directed at the most likely organisms (especially Streptococcus zooepidemicus) while awaiting culture results. Broad-spectrum coverage is often needed when mixed or anaerobic infections are possible. Supportive care includes anti-inflammatory medication, rest, and a clean, dust-free environment. Viral respiratory infections are managed primarily with rest and supportive care. Antibiotics are not effective against viruses and are reserved for confirmed or strongly suspected secondary bacterial pneumonia. Aspiration pneumonia requires prompt, aggressive broad-spectrum antimicrobial therapy that includes anaerobic coverage, plus supportive care and measures to prevent further aspiration (for example, treating the underlying choke or dysphagia). Shipping-fever pneumonia is treated with antimicrobials and supportive care. If the infection has already progressed to pleuropneumonia, additional interventions such as pleural drainage may be required. (Pleuropneumonia is covered in a separate article on this site.) For foals with clinical Rhodococcus equi pneumonia, a macrolide antibiotic combined with rifampin remains the traditional recommended treatment. Evidence is evolving, resistance is an increasing concern, and treatment of small subclinical ultrasound lesions is often unnecessary. Supportive care and monitoring for complications are essential. Antibiotics appropriate for adult bacterial pneumonia are generally not effective against R. equi. ## Recovery and Prognosis Survival is variable and depends on the case mix, severity, and presence of complications. Adult hospitalized cohorts report survival to discharge around 73% to 78%, with worse outcomes when pleural disease, anaerobic bacteria, or markers of systemic illness are present. Horses that develop large lung abscesses or require prolonged drainage have a more guarded outlook for return to full athletic performance. Foals with clinical Rhodococcus equi pneumonia have variable outcomes that depend on the severity of lung involvement, the presence of extrapulmonary abscesses, and whether antimicrobial-resistant strains are present. Some foals on endemic farms develop subclinical lesions that resolve without treatment. Aspiration pneumonia carries a more variable and often poorer prognosis, especially if large volumes of material were inhaled or if treatment is delayed. ## Prevention Vaccination against equine influenza and equine herpesvirus reduces the risk of primary viral infection and subsequent secondary bacterial pneumonia. Biosecurity practices (isolation of new or returning horses, good ventilation, and limiting nose-to-nose contact) further lower the chance of respiratory outbreaks. The strongest support for reducing transport-associated risk is allowing horses to lower their heads periodically, limiting prolonged head restraint, and improving monitoring after long-distance travel. Avoid shipping horses that are already showing signs of respiratory disease. For Rhodococcus equi, no routine vaccine is available. Evidence for hyperimmune plasma is mixed, and farm hygiene measures are promising but not definitive. Serial ultrasound screening is used on some endemic farms, but treatment of small subclinical lesions is often unnecessary. Prophylactic antibiotic use in foals is discouraged because it promotes resistance. Good dental care, gradual feed changes, and careful administration of oral medications reduce the risk of choke and subsequent aspiration. Signs include: Fever; cough; nasal discharge (clear, mucoid, or purulent); increased respiratory rate or effort; lethargy or depression; reduced appetite; in foals, poor weight gain or failure to thrive; in severe cases, labored breathing or respiratory distress
## Overview Pleuropneumonia is infection of both the lung and the pleural space. It is a severe form of pneumonia, often called shipping fever because long-distance transport with the head elevated is a major risk factor. Horses are severely depressed, febrile, and reluctant to move, with pleural fluid visible on ultrasound. Early aggressive treatment improves survival. ## Causes Mixed aerobic and anaerobic bacteria, often after transport or other stress that impairs airway clearance. ## Diagnosis Ultrasound showing pleural fluid, thoracocentesis, and culture. Bloodwork shows inflammation. ## Treatment Broad-spectrum intravenous antibiotics (covering aerobes and anaerobes), pleural drainage, and intensive supportive care. Prognosis has improved with early recognition but remains guarded in severe cases. ## Recovery and Prognosis Variable (roughly 40 to 90 percent survival depending on severity and speed of treatment). Chronic abscessation can occur. ## Prevention Minimize head elevation during long transport and allow rest stops. Signs include: severe depression; high fever; difficulty breathing; reluctance to move; pleural fluid on ultrasound
EIPH is common in racehorses and detected by post-exercise tracheal endoscopy. Inflammatory airway disease, recurrent airway obstruction, and pneumonia all affect performance. Rebreathing examination helps auscultate deeper lung fields.
Coughing, nasal discharge, labored breathing, or poor performance at speed should be evaluated. Keep dust and ammonia low in the barn to support respiratory health.
See the Diaphragm & Lungs on our interactive 3D horse model. Open 3D Model