Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 30, 1997
Publication Date: N/A
Interpretive Summary: Shipping fever of cattle is a costly disease for cattle producers in North America. A bacteria, Pasteurella haemolytica, which causes the disease often flares up in cattle herds when they are moved into feedyards. It was found that the bacteria spread among the cattle even before they get to the feedyard and that prior vaccination hindered that spread. Vaccination could slow the spread of the bacteria among cattle during a time when they are most susceptible to infection and thereby help prevent losses to cattle producers from pneumonia.
The infectious spread of Pasteurella haemolytica was documented in a group of cattle undergoing simulated marketing conditions from farm to feedyard. Pasteurella haemolytica was cultured from nasal secretions and palatine tonsillar specimens at farms, an order-buyer barn, and after shipment to a feedyard. Twelve of 101 calves were exposed after collection at the order-buyer barn to a P. haemolytica challenge strain containing a rare deletion of a common plasmid. Twenty-seven stale calves were also mixed with the experimental calves for five days prior to shipment. Plasmid profile analysis of the isolates indicated that P. haemolytica spread horizontally among the calves to a large extent between collection at the order-buyer barn and arrival at the feedyard, and significantly during the first month of feeding. Several calves simultaneously shed P. haemolytica with distinctly different plasmid profiles. Vaccination significantly reduced P. haemolytica shedding and spread. The findings indicate that calves do not necessarily succumb to P. haemolytica from their own natural flora but rather easily and quickly become infected from other animals. Disease prevention strategies which lessen bacterial shedding might significantly slow bacterial spread.