Previous research has demonstrated that pathogen loads carried on the hides of cattle increase from the time they leave a feedlot to the time they arrive at a harvest facility. The cause of this increase is not fully understood. Initially, it was hypothesized that cross-contamination was occurring while cattle were on trucks and that the increase in pathogens might be due to the cleanliness of the trucks. A 2004 research project indicated that the cleanliness of the truck did not necessarily impact pathogen loads on hides during transport. During the course of this research, the investigators observed that a cloud of dust was generated at every load-out. It was hypothesized that this air-borne particulate matter that is essentially pulverized fecal material may be at least partially responsible for the increase in pathogen prevalence. A subsequent research project supported that assumption. Exposure to the air-borne particulate matter generated from the surface of loading pens significantly increased the prevalence and quantity of E. coli O157 and Salmonella recovered from cattle hides.
Feedlot load-out areas may be a critical control point in reducing pathogen loads on beef carcasses. Control measures should be investigated to prevent increases in pathogen loads and ultimately to reduce pathogen loads on carcasses and in ground beef.
This research project was designed to determine if preventing dust generation would result in a decrease in Salmonella pathogen numbers by comparing results from a clean concrete load-out area in a feedlot versus a dirt loading area with no dust control measures.
Cattle were sampled in five separate intervals in a commercial feedlot. Approximately 30 animals (one truckload) were sampled for each treatment before being loaded onto a truck. The control treatment included holding pens and a loading area with a dirt surface that was not cleaned, while the experimental area had concrete surfacing that had been cleaned.
Animals were sampled after being removed from their “home pens.” They were then exposed to the dusty holding pen for three minutes to approximate the amount of time it takes to load a truck. The cattle were sampled a second time and then loaded on trucks to be transported to a harvest facility where additional samples were collected prior to the hides being removed. The animals in the experimental group were sampled at the same intervals, but were loaded out of pens with a clean concrete surface.
On each day of sampling, a total of 30 to 38 animals per treatment group were tested resulting in at least 60 animals per day for a period of five days. This resulted in a total of 600 hide samples collected prior to loading, with an additional 300 hide samples collected at the harvest facility.
Hides were sampled using sterile sponges hydrated with buffers. The swabs were taken at the dorsal midline and withers. A consistent sampling area was used on all cattle to facilitate both quantification and enumeration of Salmonella in the samples. Quantification helps determine not only if the pathogen was present, but also if the pathogen load increased on the cattle when they passed through the dusty area.
Air and dirt samples were also collected in the feedyard in the cattle’s “home pens” and in the load-out areas. In the loading area, the air samples were collected with a sampling apparatus before the animals entered the loading area, during dust production and 10 minutes after dust production for a total of nine samples per treatment per day. A total of 202 air samples were collected, and an additional 405 dirt or swab samples from sites within the load-out areas were also collected.
The researchers found no changes in the total population or total number of animals that tested positive for Salmonella before or after loading or between the clean and dirty load-out areas. On average, 80 percent of the animals at all sampling locations tested positive for Salmonella.
Samples collected from the pen floors in both the clean and dirty load-out areas were 100 percent positive for Salmonella. Very little of the Salmonella appeared to be transferred to the air. In the clean load-out area, no Salmonella was detected in the air samples, while in the dirty area 15 percent of the air samples tested positive for Salmonella.
The high initial Salmonella incidence on the hides of the cattle meant that the small amounts that appeared to be transferred to the air did not have significant impacts on the pathogen status of the animals.
This work indicates that feedlot loading areas and the dust cloud generated during loading can be factors in increasing pathogen loads on the animals before and after shipping. However, because of the high contamination levels on the cattle hides initially, it was not possible for the researchers to detect measurable differences on the cattle hides after they were exposed to various loading conditions.