Acute or atypical interstitial pneumonia (AIP) is terminology used by veterinary pathologists to describe a characteristic pattern of damage in the lungs of cattle. At necropsy, the first indication of AIP-affected lungs is they fill the thorax and do not collapse like normal lungs when the chest cavity is opened. On further investigation, the AIP lungs are found to be semi-firm with a rubbery texture; not hard and consolidated as occurs in bacterial bronchopneumonia. Large air bubbles are found between portions of the lung (see Figure 1, “interlobular” or “bullous” emphysema) and the cut surface of the lung may appear wet or shiny due to edema. Affected lobules are dark red to purple and may be interspersed with normal looking lobules, creating a “patchwork” or “checkerboard” appearance.

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This is part of the Forage-Related Cattle Disorders series.