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This thesis investigated the role of European starlings (Sturnus vulgaris) in the dissemination of Escherichia coli O157:H7, Salmonella spp. and antimicrobial resistant E. coli in Ohio dairy cattle farms. Using a repeated cross-sectional study of 150 Ohio dairy farms, the following were investigated: 1) associations between farm management and environmental factors, and on-farms starling density (number of starlings per milking cow); 2) associations between farm management and environmental factors, including on-farm starling density, and the presence of fecal pats with cefotaxime and ciprofloxacin resistant E. coli; 3) the role of starling night roosts in the dissemination of cefotaxime and ciprofloxacin resistant E. coli to dairy farms; and 4) using longitudinal data from a subset of study farms, the temporal pattern of contamination of cattle feed by European starling excreta and the temporal pattern in recovering E. coli O157:H7 and Salmonella spp. from these bird droppings. On-farm starling density was associated with year of bird count, and feed and manure management on dairy farms. However, proximity to night roosts, rather than day time starling numbers was associated with the risk of pats testing positive for antimicrobial resistant E. coli. In addition, statistically significant spatial clusters of cefotaxime and ciprofloxacin resistant E. coli were identified on farms around night roost sites, further implicating night roost sites as centers for the dissemination of antimicrobial resistant bacteria to dairy farms. The recovery of E. coli O157:H7 or Salmonella spp. from bird droppings was related to the amount of contamination of cattle feed by starling excreta after controlling for season. Starlings may play an important role in the epidemiology of zoonotic pathogens and antimicrobial resistant organisms on dairy farms. The findings from this thesis are important for developing risk assesment tools and planning farm biosecurity policies and procedures against the introduction of these organisms to livestock facilities. The United States Department of Agriculture through their National Research Initiative (USDA-NRI), Epidemiological Approaches to Food Safety Grant # 2006-01227

Avian intestinal spirochetosis is a disease of poultry caused by the spirochete bacterium Brachyspira, and is characterized by increased mortality, reduced egg production, weight loss, diarrhoea, and fecal staining of egg shells, which leads to downgrading of eggs. The presence of Brachyspira species in Ontario layer chicken flocks and its association with downgrades for dirty eggs was explored. Further, farm interviews were conducted to determine risk factors associated with the presence of Brachyspira species. The prevalence of Brachyspira species was significantly higher in flocks with a higher proportion of dirty eggs (dirty flocks) compared to those with a lower proportion of dirty eggs (clean flocks). Brachyspira pilosicoli was the only pathogenic species detected. Risk factors associated with the presence of Brachyspira species were flock age, barn age, multi-age farms, and housing type. Based on these findings, recommendations were suggested to control the occurrence of Brachyspira species and the associated dirty egg problem. Animal Health Laboratory