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Despite intensive research efforts, pre-harvest strategies that substantially reduce E. coli O157:H7 and Salmonella in cattle have not been identified. The associations between fecal and hide prevalence of the live animal and contamination of the carcass indicate an important role for preharvest control of E. coli O157 and Salmonella in cattle toward reducing the risk of contaminated product. In particular, interventions and management practices that reduce hide contamination should substantially reduce carcass contamination during processing (Nou et al., 2003; Bosilevac et al., 2005). In addition, successful strategies will include practices that disrupt the cycling of pathogens in the cattle production environment and reinfection of the herd.
The soils at the feedlot pen surface are likely a significant source of pathogens for contamination of the hide and may also be an important reservoir for E. coli O157 in cattle production. Feedlot soils are the medium in which bovine feces are deposited and where it collects during the finishing period. We have demonstrated that E. coli O157 can persist in feedlot soils over a wide range of moisture and manure contents, and that this pathogen can even multiply in these soils when conditions are appropriate (Berry and Miller, 2005). Smith et al. (2001) found higher E. coli O157:H7 fecal prevalence among cattle in muddy pens as compared to cattle in pens in a normal condition, indicating that the muddy pen soil environments may facilitate the fecal-oral transmission among cattle. In a longitudinal feedlot study, LeJeune et al. (2004) found that a few unique genetic subtypes of E. coli O157 persisted in the cattle, despite a large turnover in cattle population, indicating that the feedlot environment plays an important role as a source of transmission of this pathogen to cattle.
The proposed experiments were conducted to clarify the role of feedlot soils in the transmission and persistence of E. coli O157 and Salmonella
in cattle and the production environment, in addition to identifying an alternative feedlot pen surface for potential mitigation of hide contamination and reduction of pathogen persistence in manures and the production environment. Pond ash is a low cost byproduct of coal-fired electricity generation and provides a hard surface when packed into layers. This surface is currently being examined as an alternative feedlot pen floor surface; benefits include the provision of a solid base during wet weather, thus improving footing for cattle, an easier-to -clean surface, and it may also provide a cleaner area for cattle to rest in, thus alleviating some of the problems associated with muddy pens (dirty animals, loss of traction, stress, and effort expended for walking through mud). In addition to examining target pathogen persistence in the manures from the two different pen surfaces, the levels and survival of generic E. coli were determined, as process indicators of how similar enteric Gram-negative pathogens would fare. The probable compositional differences in manures (higher soil content for soil surface vs. higher organic matter content for pond ash surface) were anticipated to affect pathogen and fecal bacterial persistence in these wastes. Thus, in addition to reducing hide contamination and persistence of pathogens in cattle production, the pond ash pen surface may reduce the risk for pathogen contamination of feedlot runoff. Furthermore, it is likely that the value of the manure from pond ash surfaces will be greatly increased over the value of manure from a typical soil surface, due to the lower soil content of the manure.
Studies examining the effects of environmental stressors on shedding of pathogens and other fecal bacteria by cattle have identified numerous stresses which may sometimes impact the shedding of these bacteria, including transport, weaning, relocation, crowding, confinement, and dietary changes. The impact of heat stress on the prevalence of shedding of E. coli O157:H7 or Salmonella was examined in lactating dairy cattle by Edrington et al. (2004), who did not observe a clear effect of heat stress. However, the number of cattle and sampling were limiting, and the magnitude of heat stress was measured only by calculation of a temperature-humidity index. This study described herein examined beef cattle, and included multiple microbiological, observational, and physiological measurements of the cattle, including measurements that indicated the magnitude of heat stress of the individual animals. Information is needed regarding any potential impact of cattle heat stress level, stress risk factors, and/or interactions of these factors on the prevalence or the levels of E. coli O157:H7 or Salmonella shed in feces, so that minimization of colonization and shedding of these pathogens can be achieved.
The stated objectives for this work were:
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