Seasonal incidence and molecular characterization of Salmonella from dairy cows, calves, and farm environment.

The occurrence patterns and molecular characteristics of Salmonella are important for surveillance and control of the pathogens. Objectives of this study were to determine month-to-month variation and seasonal effects on the occurrence of Salmonella in dairy animals and environments and to characterize selected Salmonella isolates. A total of 7680 animal and environmental samples, collected monthly from a dairy farm, were analyzed for the presence of Salmonella during a 12-month study. Major sources of Salmonella on the dairy farm (% positive) were milking parlor air (62%) and bird droppings (63%) during winter; feeds (50-58%), water (53-67%), calf bedding (63%), soils (60-63%), milking parlor air (60%), and bird droppings (50%) in spring; all animal and environmental samples (40-92%) except milking parlor air (25%) and bulk tank milk (29%) in summer; and feeds (60-71%), cow beddings (59%), cow soils (50%), air (46-71%), and insects (63%) during fall. Salmonella ribotyping indicated that most serovars came from different sources but some might have originated from a common source and transmitted from site to site on the farm. These data provide some important information on key animal and environmental sampling sites needed to initiate on-farm management programs for control of this important foodborne pathogen.