Interstitial pneumonias in foals and adult horses

Interstitial pneumonias (IP) are uncommon in both adult horses and foals and often result in insidious structural change in the lungs and marked respiratory dysfunction. Rather than a specific entity, the term interstitial pneumonia encapsulates several diseases with infectious or non-infectious aetiologies that may be acute or chronic. Irrespective of cause, the pulmonary responses to injury are similar. After initial parenchymal injury and alveolitis, a proliferative phase of cellular and parenchymal changes in the lung develops, that with chronicity results in pulmonary fibrosis.1 These structural changes results in reduction in the number of functional alveoli, ventilation-perfusion mismatching and greater diffusion distances at the alveoli with the net effect of loss of functional gas exchange and lung compliance, restrictive breathing patterns, increased work of breathing and signs of increased respiratory effort or distress.