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A disease of the lower airways causing cough and exercise intolerance in horses

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So what is normal anyways? Our understanding of "normal BAL cytology" is still evolving from research and clinical experience. Different values for normal among laboratories relate to the technique used for performing BAL (e.g. volume infused, dwell time of fluid, handling and processing, interpretation of cell type) and the criteria for a normal horse used for study. For example, one might classify horses as 'normal' based on lack of clinical signs alone. Alternatively, one might use more stringent criteria and eliminate horses with tracheal mucus or radiographic changes. The ideal 'normal' has not been established.

A normal horse in our clinic meets the following criteria:

  • no clinical signs of SAID
  • normal endoscopy after exercise (no mucus)
  • normal airway reactivity (doubling of airway resisance at > 6 mg/ml histamine)
  • in full work with no history of exercise intolerance

Using these criteria and our technique for BAL, our reference range for nucleated cell counts is as follows:

AM Alveolar Macrophages 50-70%
L Lymphocytes 30-50%
PMN Neutrophils <5%
MC Mast cells <2%
EOS Eosinophils <0.5%
HSP Hemosiderophages  

Gallery of BAL Cells

Mast cells (MC) are generally seen early in SAID.


Hemosiderophages (HSP) are seen in EIPH horses (bleeders).


Neutrophils (PMN) are more prevalent in advanced cases of SAID and COPD.


Eosinophils (EOS) are a sign of allergic disease and have been reported in early SAID.


Mucous in the airways is a frequent consequence of SAID.


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