Analysis of risk factors associated with Salmonella spp. isolated from U.S. feedlot cattle

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] = 26.35; confidence interval [CI], 10.33-67.20), corn gluten (OR = 10.35; CI, 5.98-17.91), or cottonseed hulls (OR = 8.34; CI, 3.58-19.42) in the ration, and sourcing animals in a pen from multiple herds of origin (OR = 5.17; CI, 2.32-11.51). Factors negatively associated with positive culture status included urea (OR = 0.27; CI, 0.16-0.44), alfalfa, clover, or sorghum silage (OR = 0.31; CI, 0.12-0.79), and antimicrobials of the tetracycline class in the ration (within 2 weeks before sampling, OR = 0.04 and CI, 0.02-0.09; more than 2 weeks before sampling, OR = 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 = 2.99; CI, 1.55-5.75), soybean meal (OR = 2.74; CI, 1.58-4.75), and use of a coccidiostat in the ration (OR for no coccidiostat = 4.50; CI, 2.03-10.01). Considering the increasing use of by-products of the biofuel industry as feeds, further investigation of the association between feeding brewers' grains and corn gluten and Salmonella recovery is warranted.