|Byrd Ii, James|
Submitted to: Zoonoses and Public Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2010
Publication Date: 7/1/2010
Publication URL: http://handle.nal.usda.gov/10113/57252
Citation: Volkova, V.V., Wills, R.W., Hubbard, S.A., Magee, D.L., Byrd II, J.A., Bailey, R.H. 2010. Risk factors associated with detection of Salmonella in broiler litter at the time of new flock placement. Zoonoses and Public Health. 58:158-168. Interpretive Summary: Reducing the burden of Salmonella in broiler flocks presents a challenge for the public’s health. To understand the spread of Salmonella from one group of chickens to the next group, our laboratory studied the litter that newly hatched chickens were placed upon. The broiler industry has widely accepted the use of pine wood chips, a byproduct, for use as broiler house floor litter. Of almost 370 factors considered, the screening process identified 24 factors that contributed to the Salmonella status in litter. These variables included surroundings of the house, house construction and conditions, litter management, downtime between flocks, biosecurity, and farm location. Salmonella in litter was strongly associated with the use of wood to construct the base of walls or to cover the inside of the foundation of the broiler house, and also with the use of fresh wood shavings to add to the floor or completely replace the litter between groups of birds. To the best of the authors’ knowledge, this is the first field report of such associations.
Technical Abstract: The effects of Salmonella being present in the broiler house environment at the time of broiler placement upon the persistence of the pathogen throughout the production and processing continuum are yet to be fully elucidated. In this study, we investigated risk factors associated with the detection of Salmonella in samples of litter collected within two hours prior to new flock placement in 76 grow-out houses on 38 conventional broiler farms. The risk factors evaluated included: i) location and layout of the farm; ii) area adjacent to and surrounding the house; iii) house construction; iv) condition and type of equipment in the house; v) litter and other production management practices; vi) sanitary and biosecurity practices; vii) non-broiler animal species on the farm; and viii) weather conditions on the three days leading up to flock placement. Logistic regression was used to model the relationships between detection of Salmonella in litter and the potential risk factors. In the screening process, each risk factor was evaluated as a single fixed effect factor in a multilevel model that accounted for variability among the sampled farms and their production complexes and companies. Of almost 370 risk factors considered, the screening process identified 24 variables associated with the detection of Salmonella in litter. These variables included surroundings of the house, house construction and conditions, litter management, downtime between flocks, biosecurity, and farm location. Through investigation of collinearity and intermediate models, the list of candidate variables for the final model was refined to eight factors. The final model demonstrated that the detection of Salmonella in litter was strongly associated with the use of wood to construct the base of walls or to cover the inside of the foundation of the broiler house, and also with the use of fresh wood shavings to top-dress or completely replace the litter between flocks.