Pulmonary hypertension in a group of dairy calves

An episode of pulmonary arteritis and sclerosis in twenty 5- to 6-month-old dairy calves was investigated. Sixteen of the calves died acutely, without marked premonitory signs of disease. Four calves evaluated clinically had lethargy, pallor, weakness, tachycardia, tachypnea, and jugular venous distention. Cardiac catheterization performed in 3 of the calves revealed pulmonary hypertension; 1 of these calves survived. Necropsy findings in 19 calves included pale lungs and excess free fluid in the pleural and abdominal cavities. In addition, 13 of 19 calves had a dilated and thin-walled right ventricle; 4 of the calves had right-sided cardiac hypertrophy, and 2 had dilatation of the pulmonary artery. Microscopically, pulmonary arteritis and sclerosis of the small to medium-sized arteries were evident in all calves submitted for necropsy. A lung biopsy specimen from a surviving calf had similar lesions. Centrilobular hepatic necrosis was found in 17 of 19 calves. Investigation of the disease episode, including feed analysis for toxins and serologic and microbiological studies of clinically affected calves and clinically normal in-contact penmates, failed to reveal any associated risk factor. The pulmonary arterial changes in the calves were similar to lung lesions in rats fed monocrotaline.