Project Summary

Impact of Dust “A Pathogen Cloud” During Loading of Feedlot Cattle for Transportation to the Harvest Facility on the Prevalence of E. coli O157:H7 and Salmonella spp.

Principle Investigator(s):
Mark Miller, Ph.D.
Texas Tech University
Completion Date:
February 2006



During the loading of cattle at the feedyard it is a common occurrence for a dust cloud to form. This dust cloud could conceivably a source of cross-contamination as animals pass through it during loading.

The objective of this study was to determine if a dust cloud created during the loading of cattle resulted in significant cross-contamination of E. coli O157 and/or Salmonella during cattle transport.


During the months of August and September, 2005, a total of 250 cattle were sampled during loading into trucks to be transported to a slaughter facility. The hides of the animals were sampled twice. They were initially sampled on the left side and then sampled on the right side after proceeding through the dust cloud. In addition to sampling the hides, air samples were collected as well as dirt samples in the snake area (area before the chute) and from the pen from where the animals were removed. The presence and the quantitative amount of E. coli O157 and Salmonella spp in all samples were then determined.


  • Loading of cattle results in significant increases in quantitative numbers of Salmonella and E. coli O157 present on cattle hides.
  • Comparing individual animals before and after sampling:
    • A total of 14% of the animals that tested negative for E. coli O157 became positive after loading
    • A total of 18% of the animals that tested negative for Salmonella became positive after loading
  • Cross-contamination occurs at some point during loading resulting in higher pathogen loads on cattle going onto a truck than they were when they left the pen
  • Both Salmonella and E. coli O157 were recovered from the dust in the air that was generated during cattle loading.
  • When Salmonella was detected in the air, there was a significant increase in the total quantitative amount of Salmonella present and in the number of animals that test positive indicating the dust generated during loading could be a source of contamination during loading.
  • When Salmonella was present in the highest amounts in the pen and snake areas, the pathogen loads were the highest on the cattle. Only 3 samples of 50 taken from the pen were positive for E. coli O157. However, in the snake area, there were 13 positives with no differences before and after
  • indicating the E. coli O157 survives in the snake area from day to day. The snake area could be a source of contamination of the hides during loading.
  • For Salmonella, approximately 50% of samples taken from both the pen and snake areas were positive. There appears to be little difference in the snake area before and after loading.
  • There was an increase in the pathogen loads on cattle hides due to the loading process. This appears to be correlated to the pathogen presence in the air at the loading area of the snake.


These observations indicate that the loading areas and the dust cloud generated during loading can be primary factors in increasing pathogen loads on the animals before and after shipping. Control measures should be investigated to prevent increases in pathogen loads and ultimately to reduce pathogen loads on carcasses and in ground beef.