Pathophysiologic studies of infectious bovine rhinotracheitis in the Holstein-Friesian calf.

Pulmonary function changes in 6 Holstein-Friesian calves, 4 to 8 weeks of age, were studied for 10 to 11 days following experimental inoculation with infectious bovine rhinotracheitis (IBR) virus. Calves had no demonstrable antibody titer against IBR virus before inoculation, and all calves responded to the virus by postinoculation day 3 with high fever (greater than 40.6 C) and rapid, shallow breathing. Analysis of blood gases demonstrated a progressive rise in PaCO2 but no change in PaO2. Acid-base state remained normal. Tidal volume decreased with time; conversely, minute ventilation functional residual capacity, O2 consumption, and CO2 production increased. Alveolar ventilation failed to increase as much as predicted. Studies of respiratory mechanics showed a progressive increased in total pulmonary resistance but without change in dynamic pulmonary compliance. A steady-state N2 washout test was used with these calves, and results suggested impairment of intrapulmonary gas mixing as the disease progressed. Microbiologic, pathologic, and histopathologic analyses were consistent with the picture of acute IBR. This study demonstrated our ability to measure pulmonary function changes in nonanesthetized large animals suffering from respiratory tract disease. We characterized the pathophysiologic features of acute IBR infection in the bovine species as an obstructive lung disease resulting in increased resistance to breathing, retention of CO2, and increased resting lung volume.