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

Author
item GREEN, A - COLORADO STATE UNIV
item DARGATZ, D - USDA-APHIS
item WAGNER, B - USDA-APHIS
item Cray, Paula
item Ladely, Scott
item KOPRAL, C - USDA-APHIS

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2010
Publication Date: 7/1/2010
Citation: Green, A.L., Dargatz, D.A., Wagner, B.A., Cray, P.J., Ladely, S.R., Kopral, C.A. 2010. Analysis of risk factors associated with Salmonella spp. isolated from U.S. feedlot cattle. Foodborne Pathogens and Disease. 7(7):825-833.

Interpretive Summary: Salmonella is a zoonotic pathogen which can be transferred from animals to humans, most often through consumption of contaminated food. Infection with Salmonella can cause mild to severe gastroenteritis in humans while infection in food animals is often with clinical signs of disease. In order to develop effective intervention and control measures, it is important to ascertain the factors that may affect the detection of Salmonella from cattle in US feedlots. During each of 2 visits to 73 feedlots, for each of three pens, 25 fresh fecal samples were collected off pen floors. All fecal samples were cultured for Salmonella and associations between factors and culture status were evaluated. Having a single herd of origin for cattle in a pen was 5 times as likely to account for the detection of Salmonella. Additionally, use of specific ingredients in rations, particularly urea, cottonseed hulls alfalfa, clover, or sorghum silage, corn gluten, brewers grains, and tetracycline class antimicrobials (but not within 2 weeks prior to sampling) were identified as possible risk factors. Three additional variables fit the risk model including grain processing method (dry roll, cracked, or unprocessed whole grain), soybean meal (OR = 2.74, CI, 1.58–4.75), and use of a coccidiostat in the pen. Further study is needed to understand the roles of various management and feed-related factors in the shedding of Salmonella in feedlot cattle. These data are necessary to enable a more informed debate among scientists, commodity groups, government regulators, and animal industry personnel on the feasibility or identifying possible intervention areas for control of Salmonella as a means to reduce the incidence of human salmonellosis.

Technical Abstract: This study examined risk factors for detection of Salmonella from cattle in U.S. feedlots. During each of 2 visits to 73 feedlots, for each of three pens, 25 fresh fecal samples were collected off pen floors. Associations between factors and culture status were evaluated. Variables were considered for inclusion in a multivariable logistic regression model if the chi-square P value <0.25. Since 18.3% of positive samples were on a single operation, a second model was constructed after excluding this operation. A backward elimination approach was utilized until all variables remaining in the model were significantly associated with the outcome (P < 0.05). Variables from the model with the full dataset that were retained in the final model included having a single herd of origin for cattle in a pen (OR for different origins = 5.17, CI, 2.32–11.51) and the following ration ingredients: urea (OR = 0.27, CI, 0.16–0.44), cottonseed hulls (OR = 8.34, CI, 3.58–19.42), alfalfa, clover, or sorghum silage (OR = 0.31, CI, 0.12–0.79), corn gluten (OR = 10.35, CI, 5.98–17.91), brewers grains (OR = 26.35, CI, 10.33–67.20), and tetracycline class antimicrobials (within 2 weeks prior to sampling, OR = 0.04, CI, 0.02–0.09; yes but not within 2 weeks prior to sampling, OR = 0.23, CI,0.06–0.80). Three additional variables fit this model including grain processing method (OR for dry roll, cracked, or unprocessed whole grain = 2.99, CI, 1.55–5.75), soybean meal (OR = 2.74, CI, 1.58–4.75) ,and use of a coccidiostat in pen rations (OR for no coccidiostat = 4.50, CI, 2.03–10.01). Further study is needed to understand the roles of various management and feed-related factors in the shedding of Salmonella in feedlot cattle.