Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 24, 1996
Publication Date: N/A
Interpretive Summary: Pasteurella haemolytica is the bacterium that causes the greatest incidence of pneumonia in cattle and sheep. More than 15 types of the bacterium are known, but type 1 is most prevalent in cattle. Cattle were vaccinated with an experimental vaccine for the bacterium and were transported to a feedyard, where a respiratory disease outbreak occurred. Vaccination reduced the incidence of infection, but did not reduce the incidence of the respiratory disease. The incidence of both infection and disease were related to the farm of origin and to levels of serum antibody against the bacterium at the farm. The incidence of infection was reduced by vaccination.
Calves (n=104) originated from 4 farms, where half the calves on each were vaccinated. The calves were delivered to an order-buyer barn 95 to 98 days later, and were mixed with 11 calves, none of which were febrile or had clinical signs of disease. After 6 dahs at the order buyer barn, calves were shipped 1,600 km by truck to a feedyard, and arrived the next day. At the feedyard, a respiratory tract disease occurred, involving 73 calves, which were treated with antibiotics. On the second day at the feedyard, a second vaccination was administered to the vaccinates. At the farm, order buyer barn, and on 4 occasions at the feedyard, nasal secretion and tonsil wash specimens were tested for the presence of P. haemolytica and serum titers were measured. The incidence of respiratory tract disease was significantly influenced by the farm of origin, and by serum titer to P. haemolytica at the farm, but was not influenced by vaccination. Isolation of P. haemolytica, however, was influenced by vaccination as well as the other 2 factors. The major serotype of P. haemolytica encountered was serotype 1, but serotype 6 was isolated from calves on 1 farm and spread among the others. Selectively lowering the frequency of colonization by P. haemolytica serotype 1 could reduce losses to pneumonic pasteurellosis.