Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Microbiology and Preventive Medicine

First Advisor

James S. Dickson


This dissertation focuses on Salmonella in the pre-harvest portion of pork production. Nearly all of the current research in this area has focused on the prevalence of Salmonella in swine, with little attention being paid to quantifying positive sample. The purpose of this dissertation was to demonstrate the usefulness of quantitative data in identifying critical control points in pre-harvest pork production.;The current method for enumerating Salmonella, the most probable number method (MPN), is time consuming, labor intensive and cumbersome. In order to facilitate the acquisition of quantitative data, a new, less labor intensive, variation of the MPN method (the RX tube) was developed and validated. This method was determined to be equivalent to the MPN method.;Using this method, quantitative data was collected from 210 animals (for cecal contents, feces and ileocecal lymph nodes) at three Midwest abattoirs. Using this quantitative data a distribution of the Salmonella load for each sample type was established. The average load for cecal contents and feces was 102 CFU/g while the average load for ileocecal lymph nodes was 103 CFU/g. For all sample types, the distribution was skewed towards lower loads of Salmonella.;Using this quantitative data, a hazard analysis model for pre-harvest pork production was created. The quantitative nature of this model allowed the prediction of infections prevented by potential critical control points, something most current models are unable to do. It was determined that the final weeks of finishing and transport/holding are potential critical control points, both from a prevalence and infection standpoint.;This dissertation was designed to illustrate the advantages of using quantitative data in hazard analyses. It is hoped that the development of a simplified method coupled with an illustration of the usefulness of quantitative data will encourage other researchers to collect quantitative as well as prevalence data.



Digital Repository @ Iowa State University,

Copyright Owner

Jared Keith Gailey



Proquest ID


File Format


File Size

98 pages