Analysis of Risk Factors Associated with Salmonella spp. Isolated from U.S. Feedlot Cattle Alice L. Green, 1 David A. Dargatz, 2 Bruce A. Wagner, 2 Paula J. Fedorka-Cray, 3 Scott R. Ladely, 3 and Chris A. Kopral 2 Abstract Contamination can occur at a number of stages during farm-to-fork processing. Preharvest intervention is an ongoing area of interest in reduction of risk of foodborne illness. This study examined risk factors associated with detection of Salmonella from cattle in U.S. feedlots. During two visits to 73 feedlots, 25 fresh fecal samples were collected from each of three pen floors. Associations between management and demographic factors and culture status were evaluated using logistic regression. Factors positively associated with culture-positive status included brewers’ grains (odds ratio [OR] ¼ 26.35; confidence interval [CI], 10.33–67.20), corn gluten (OR ¼ 10.35; CI, 5.98– 17.91), or cottonseed hulls (OR ¼ 8.34; CI, 3.58–19.42) in the ration, and sourcing animals in a pen from multiple herds of origin (OR ¼ 5.17; CI, 2.32–11.51). Factors negatively associated with positive culture status included urea (OR ¼ 0.27; CI, 0.16–0.44), alfalfa, clover, or sorghum silage (OR ¼ 0.31; CI, 0.12–0.79), and antimicrobials of the tetracycline class in the ration (within 2 weeks before sampling, OR ¼ 0.04 and CI, 0.02–0.09; more than 2 weeks before sampling, OR ¼ 0.23 and CI, 0.06–0.80). Since 18.3% of positive samples were on a single operation, a second model was constructed after excluding data from this operation. Three additional variables were retained in the second model, including grain-processing method (OR for dry roll, cracked, or unprocessed grain ¼ 2.99; CI, 1.55– 5.75), soybean meal (OR ¼ 2.74; CI, 1.58–4.75), and use of a coccidiostat in the ration (OR for no coccidiostat ¼ 4.50; CI, 2.03–10.01). Considering the increasing use of by-products of the biofuel industry as feeds, further investi- gation of the association between feeding brewers’ grains and corn gluten and Salmonella recovery is warranted. Introduction S poradic Salmonella infections have been estimated to account for approximately 1.4 million cases of illness, 15,000 hospitalizations, and 400 deaths annually in the United States (Voetsch et al., 2004). Annual cost estimates range from $0.5 to $2.3 billion (Frenzen et al., 1999; Mead et al., 1999). Infection may develop after consumption of Salmonella- contaminated animal-origin foods or fruits and vegetables. Contamination may occur during production, transport, slaughter, processing, storage, retail, and food preparation (Hogue et al., 1998). To reduce the likelihood of carcass contamination with Salmonella and other foodborne pathogens, numerous inter- vention strategies have been implemented in harvest facilities (Reed, 1995). Additionally, there is ongoing interest in pre- harvest strategies for reducing pathogen load in the gastro- intestinal tracts or on the hides of animals (Attenborough and Matthews, 2000; Stephens et al., 2007). To facilitate preharvest intervention, additional understanding of the complex dis- tribution of these pathogens in the feedlot setting is needed. Salmonella transmission to cattle on-farm can occur in many ways. Feed ingredients such as corn, hay, silage, cottonseed, and other additions may be contaminated by wild birds (Kapperud and Rosef, 1983; Malmqvist et al., 1995; Refsum et al., 2003), mammalian carriers (Davies and Wray, 1995; Malmqvist et al., 1995; Letellier et al., 1999), or surface-water runoff while in the field (Vaessen et al., 1998). Contamination may occur during processing, transport (Fedorka-Cray et al., 1997; Dargatz et al., 2005), or on-site. Ingestion of contami- nated surface water (Fossler et al., 2005b) or water from con- taminated troughs (Branham et al., 2005) can also result in transmission. Additionally, animal-to-animal transmission may occur (Khaitsa et al., 2007), and management factors are likely to play a role (Fossler et al., 2005b). Knowledge of risk factors affecting Salmonella shedding can assist in planning 1 Tennessee Department of Health, Communicable and Environmental Disease Services, Nashville, Tennessee. 2 Centers for Epidemiology and Animal Health, Animal and Plant Health Inspection Service, Veterinary Services, U.S. Department of Agriculture, Fort Collins, Colorado. 3 Richard B. Russell Research Center, Agricultural Research Service, U.S. Department of Agriculture, Athens, Georgia. FOODBORNE PATHOGENS AND DISEASE Volume 7, Number 7, 2010 ª Mary Ann Liebert, Inc. DOI: 10.1089=fpd.2007.0068 825