To measure the level of antimicrobial resistance in potential bovine respiratory pathogens at different production
types, nasal swabs were collected from 57 calves of 13 dairy herds, 150 calves of 9 beef cattle herds,
and 289 calves of 5 high-density veal calf herds and investigated for the presence of Pasteurellaceae. All calves
were less than 6 months old. Susceptibilities of the Pasteurella and Mannheimia isolates to eight antimicrobials
were determined using an agar dilution method. P. multocida (37.3%) and hemolytic Mannheimia organisms
(M. haemolytica sensu lato) (6.3%) were the most frequently detected organisms. The overall prevalence
of isolates resistant to at least one antimicrobial from the dairy, beef, and veal calves were 17.6% (6/34),
21.9% (14/64), and 71.9% (64/89), respectively. In isolates obtained on the veal calf herds, acquired resistance
to ampicillin, oxytetracycline, potentiated sulfonamides, gentamicin, tilmicosin, and enrofloxacin was frequently
present, and 32.6% of these isolates were resistant to more than two of the tested antimicrobials. Resistance
to ceftiofur and florfenicol was not detected. A substantial within-herd variability of species diversity
and resistance profiles among isolates belonging to the genera Pasteurella and Mannheimia was found
among the isolates of the veal calf farms.
