Prevalence of Pasteurella haemolytica in transported calves.

In 2 different years, calves from individual farms were sampled by nasal swab for Pasteurella haemolytica at the farm, at an auction barn, and at a feedyard after they had been transported 1,600 km. Serum antibody titers were determined and P haemolytica isolates were serotyped. The frequencies of P haemolytica isolations were low at the farm, greater at the auction barn, and markedly high at the feedyard. Serotype 2 was the predominant isolate at the farm, and serotype 1 was the predominant isolate at the feedyard and from the pneumonic lungs of the calves that died of acute respiratory tract disease. There was a significant farm-to-farm variation in the percentages of calves that developed respiratory tract disease.