Epidemiology of Salmonella infection and shedding in Ohio dairy herds

The purpose of this research was to describe the epidemiology of Salmonella infection and fecal shedding in Ohio dairy herds. The objectives of the first study were to estimate the prevalence of Salmonella fecal shedding in Ohio dairy herds and to determine potential risk factors for shedding of the organism. We found that fecal shedding of Salmonella is common in Ohio dairy herds, with 31% of farms having at least one animal shedding Salmonella in the feces at any point in time. Larger herds were twenty times more likely to be Salmonella positive. We could not identify specific management practices that might reduce the risk of Salmonella shedding in dairy herds, nor could we find any effects of Salmonella shedding status on estimated milk production.; The objectives of the second study were to monitor subclinical Salmonella fecal shedding in naturally infected dairy herds and to determine effects of infection on production. A high prevalence of Salmonella fecal shedding was observed in herds during an 18-month monitoring period, with no effects on production. We were unable identify specific practices that might reduce the risk of Salmonella shedding among herds, but differences in management practices within herds were detected that could help identify risk factors for infection on the individual farms.; The purpose of the third study was to describe patterns of antimicrobial resistance of Salmonella in subclinically infected Ohio dairy herds and to compare to resistance in bovine clinical isolates. Few antimicrobial-resistant Salmonella isolates were detected in herds monitored longitudinally. No significant temporal changes in antimicrobial susceptibility were observed over an 18-month monitoring period. Seventy-four percent of Salmonella isolates from a cross-sectional study of Ohio dairy farms were susceptible to all 17 antimicrobials tested. Compared to clinical Salmonella isolates from the state veterinary diagnostic laboratory, the subclinical study isolates exhibited less antimicrobial resistance. Reporting of antimicrobial resistance of clinical or diagnostic isolates may overestimate the actual amount of resistance observed in a population.