Chronic lower respiratory disease has been increasingly recognized as a cause of decreased performance in horses and increasinly we are recognizing a number of different clinical types. This problem may not present with any other clinical signs other than poor performance or cough when first exercised. In one report of clinically normal horses which compared those with normal tracheobroncial secretions to those indicative of chronic lower airway disease it was found that the post exercise respiratory recovery rate was twice as long as those with normal secretions. The exercise respiratory recovery rate is the length of time following exercise it takes for the respiratory rate to return to normal. This report contains an overview of the evaluation of a horse with a history of decreasing performance with possible lower respiratory disease. There are links to other related articles on the problem of lower respiratory disease and poor performance.

Diagnostic aids for investigation of lower respiratory tract disease include a thorough physical examination including thoracic auscultation with a rebreathing bag, a review of the feeds (particularly hay quality), CBD and blood chemistries. If further workup is warranted a endoscopic examination, bronchoalveolar lavage (BAL), and thoracic radiographics will further delineate the problem.

In cases of a cough when first exercised or obvious respiratory distress in a horse with normal temperature, attitude, and appetite, COPD should be first on the list. Support for the diagnosis is finding mold spores in the hay, ...more. In cases that do not respond to treatment for COPD, often a specific diagnosis and the therapeutic approach for horses can be directed by cytologic evaluation of BAL fluid. Causes of chronic lower respiratory disease include:

• Chronic infection with bacteria, fungus, or lungworms.
• Allergies, particularly to hay molds. Traditionally named "Heaves" of Chronic Obstructive Pulmonary Disease (COPD) more recently Recurrent Obstructive Airway Disease has been used (ROAD). In the South gulf region there is also described a Summer Pasture Associated Obstructive Disease (SPAOD).
• High levels of ammonia in the barn air or other noxious airborne chemicals.
• Possibly exercise induced pulmonary hemorrhage.
• Inflammation left over from past infectious disease. One recently described condition is Chronic Nodular Fibrosis of the lungs secondary to EHV-5 infection.
  • Clinical signs: decreased appetite, weight loss, fever, cough, tachypnea, and respiratory distress.
  • Further diagnostics: Radiography and ultrasonography reveal a nodular interstitial pneumonia pattern. Bronchoalveolar lavage fluid should be positive for EHV-5 or positve to a polymerase chain reaction assay for EHV-5.
  • Treatment: supportive, corticosteroids, and acyclovir.
  • Prognosis guarded to poor
• Inflammation with no obvious cause. Examples below include Mast Cell and Eosinophilic Pneumonia.