Past research has shown that handling and transportation of livestock can cause animals to become stressed, which can increase the shedding of fecal material and pathogens. The transportation trailer has been proposed as a possible source of the increased prevalence, but it is not known how cleaning and sanitizing trailers prior to animal transportation will affect contamination on beef hides entering the slaughter plant. In addition, animals on the lower deck of the trailer may have increased levels of contamination compared to those on the upper deck.
The objective of this project was 1) to determine the impact of transportation of beef animals to the harvest facilities on the prevalence of E. coli O157:H7 and Salmonella spp, 2) determine the impact of the animal location (upper versus lower level) during transportation on the prevalence of E. coli O157:H7 and Salmonella spp, and 3) determine the effectiveness of trailer washing as a means of minimizing hide contamination during transportation of beef animals on the prevalence of E. coli O157:H7 and Salmonella spp.
Random samples of 40 animals from the same pen at a commercial feedyard were taken. Swabs were taken from the withers and midlines of each animal. Half of the trucks to be used in the study were cleaned and sanitized prior to arrival at the feedyard. Samples were collected from the clean and dirty trailers and were collected from the front, right side, left side and floor of each level to determine microbial contamination in the trailers prior to animal contact. Ten of the study animals were loaded on the upper and lower compartments of the clean and dirty trailers with the remaining trailer space filled with cattle pen mates not part of the study. After transportation to a slaughter facility, the cattle were unloaded and kept in their respective groups (clean trailer-top level, clean trailer-bottom level, dirty trailer-top level and dirty trailer-bottom level) and the trailers were swabbed again to determine any variation in microbial population due to animal contact. Cattle were slaughtered in the respective groups and swabs of the midline and withers were taken again after exsanguination. These procedures were repeated over the course of eight days. The swab samples were analyzed for E. coli O157:H7 and Salmonella spp.
Salmonella spp Animal swabs collected showed a significant interaction for trailer and hide swabs. Swab samples collected from the midline had a higher percentage of positive samples than those collected from the withers of the animals transported in both trailers. Animal swabs taken at the harvest facility had significantly more positive samples than those taken at the feedyard at both hide swab locations. This agrees with previous research that has demonstrated that animal-to- animal contact may be a contributing factor to microbial transmission. Future research should address what the current time and space parameters are for the transmission of Salmonella spp between animals.
Trailer swabs collected for Salmonella spp analysis showed a significant interaction for location and trailer. At the feedyard, swabs taken from the clean truck (3.1 percent) had a lower percentage of positive samples than those collected from the dirty truck (71.9 percent). However, at the harvest facility, swabs taken from the clean truck (75.0 percent) had a higher percentage of positive samples than those collected from the dirty truck (71.9 percent). Location within the trailer also showed significant differences in the prevalence of positive samples. The floor samples were significantly higher than those collected from the right, left and front sides of the clean and dirty trailers.
E. coli O157:H7
There were no significant differences in E. coli O157:H7 prevalence samples taken from animal hides between the treatment groups. The researchers also saw no significant interactions on E. coli O157:H7 prevalence values from the trailer samples. A low incidence of positive samples contributed to these findings. Of the 256 swab samples taken from the trailers, less than 2 percent were positive for E. coli O157:H7.
Overall, the cleaning and the sanitizing of the trailers was not directly related to the cleanliness of the cattle, as increased prevalence levels found on animal withers and midlines at the harvest facility were not different between the animals transported in the “clean” versus the “dirty” trailers.
Even though the prevalence of Salmonella spp in the trailers showed some significant interactions; based on this study, there did not appear to be a direct relationship between the cleanliness of the trailer used in the transportation of the cattle, the level in which the cattle were transported and the actual microbial prevalence found on the hide of the cattle. Other research has also shown that the prevalence of Salmonella spp has increased due to transportation, however this project demonstrates that the trailer itself is not the source of increased contamination.
The researchers suggested that other sources of contamination besides animal contact might be the dirt and dust that is present in the loading area at the feedyard, the holding areas at the feedyard just prior to loading, holding areas at the plant prior to slaughter and the equipment and personnel found inside the plant during stunning and exsanguination. The researchers recommended that further research should be conducted to evaluate other possible contamination sources, so that producers and packers can implement pre-harvest intervention steps to reduce the prevalence of foodborne disease microorganisms.