A review of interstitial pneumonia in cattle.

Interstitial pneumonias comprise a significant proportion of cattle respiratory diseases. Known by different names, such as acute bovine pulmonary emphysema and edema (ABPE), fog fever, atypical interstitial pneumonia (AIP) and cow asthma, the condition seems to occur predominantly in late summer or fall. However, depending on the etiology, cases have occurred throughout the year. Interstitial pneumonia often begins with acute respiratory distress in animals that were clinically normal 12 hr earlier. Animals are observed breathing very rapid and shallow with their mouths open. If disturbed, death may occur rapidly from hypoxia. Causes of interstitial pneumonia are quite varied ranging from parasitic, viral and bacterial to toxic. Toxic agents constitute the most economically important cause of this condition in cattle. The primary toxin is the amino acid L-tryptophan in lush pasture grasses, a compound which is converted to 3-methylindole by rumen microorganisms. Other leading toxic causes of interstitial pneumonia are perilla mint and moldy sweet potatoes. Although treatments are mainly symptomatic and ineffective, preventive measures will reduce the occurrence of interstitial pneumonia. Prevention consists of denying animals exposure to know pneumotoxic agents, eliminating certain rumen microflora that break down the toxic compounds to reactive metabolites, and supplying ample good forage so that cattle will not as likely consume toxic plants.