Acute Respiratory Distress Syndrome of Feedlot Cattle

An acute respiratory distress syndrome has been described in feedlot cattle with clinical signs and pathologic findings of an atypical interstitial pneumonia. The syndrome occurs sporadically, and the etiology remains undefined. Feedlot heifers seem to be at higher risk of developing the disease than feedlot steers. Bovine respiratory syncytial virus, abnormal production of 3-methylindole in the rumen, dusty conditions, and preexisting lesions of chronic cranioventral bacterial pneumonia have been suggested as causes or contributing factors. Clinical signs include respiratory distress characterized by tachypnea and dyspnea, and affected cattle may be found dead if clinical signs are unobserved. Lesions are those of atypical interstitial pneumonia with prominent emphysema and edema in the lungs. Treatment protocols have not been defined; thus, treatment is symptomatic and supportive. In many cases, emergency slaughter is the most economical option. Management strategies suggested include vaccinating for bovine respiratory syncytial virus, controlling dust in the feedlot, and avoiding abrupt dietary changes.