RAPID SPREAD OF A UNIQUE STRAIN OF PASTEURELLA-HAEMOLYTICA SEROTYPE-1AMONG TRANSPORTED CALVES

Objective-To determine the rate and mode of infectious spread of Paste urella haemolytica among carves maintained under typical conditions du ring collection, transport, and the first month of feeding. Animals-10 1 two- to five-month-old Angus-crossbred calves. Procedure-Samples obt ained from cattle prior to and after they were transported to a feedlo t were used for isolation and characterization of P haemolytica. Sampl es were also obtained from additional calves, some of which were sick, and these calves were then commingled with the transported calves for 3 days. A strain of P haemolytica that contains a rare deletion of th e 4.2-kilobase streptomycin- and sulfonamide-resistance plasmid was in oculated into both palatine tonsils of 12 carves. Nasal secretions wer e aspirated from the ventral nasal meatus. Tonsillar wash specimens we re procured. Pasteurella haemolytica organisms were quantitatively cul tured and identified on the basis of colony morphology and response to specific antisera. Plasmids were isolated by an alkaline lysis proced ure and identified by agarose gel electrophoresis. Results-A single pl asmid profile was observed from P haemolytica isolated from samples ob tained prior to shipment. Commingled calves were shedding P haemolytic a containing each known plasmid profile. After shipment, samples conta ined P haemolytica isolates with each known plasmid profile. The plasm id profile of the unique P haemolytica isolate was recovered from all 12 inoculated calves and 10 other calves. Some calves simultaneously s hed P haemolytica isolates with differing plasmid profiles. Conclusion s and Clinical Relevance-Pasleurella haemolytica serotype 1 was horizo ntally transmitted among calves within days of commingling, which cont inued after calves were transported to a feedlot.