The best way to control and eliminate pathogens, such as E. coli O157:H7, is to understand their sources and prevalence in the environment. Knowing the source and level of contamination is critical for developing improved processing and intervention strategies.
Recent research conducted by scientists at the U.S. Meat Animal Research Center (USMARC) has determined that during transportation to packing plants and lairage at the facilities themselves, pathogen prevalence on cattle hides increases. The cause for the increase is currently unclear.
Previous research has shown via pulse field gel electorphoresis (PFGE) tracking that many of the isolates obtained from beef carcasses at the packing plant did not originate from the feedlot from which the cattle were shipped, nor were they present in the trucks used to transport the cattle. The researchers believe that the isolates originated from the lairage environment.
Cattle hides have been identified as a major source for carcass contamination, so intervention strategies targeted at transport and lairage environments should lead to reductions in pathogen contamination of carcasses. There is mounting evidence that pathogen prevalence on the hides of cattle increases during transport and lairage at commercial slaughter facilities. Effective preharvest intervention strategies implemented at the feedlot level or prior, may be negated by contamination during lairage. Identifying and eliminating the sources of these pathogens would greatly help in keeping the levels of pathogens as low as possible on the hides of animals coming to slaughter.
The objectives of this study were, 1) determine the extent to which lairage adds to E. coli O157:H7 prevalence and loads on cattle hides, 2) identify sources of E. coli O157:H7 in the lairage environment, and 3) work with the beef processing industry to identify and implement intervention strategies targeted to the lairage environment.
Feedlot cattle (n = 583) were followed from the U.S. Meat Animal Research Center feedlot to slaughter. The cattle were shipped as six separate lots and were divided among three commercial processing plants with two separate trips to each plant. The individual lots remained separate through trucking and were housed in separate locations in the processing plant holding pens.
Hide swabs and fecal samples were collected one day prior to transport. Before the cattle were loaded on trucks the next day, the researchers collected six sponge samples from the inside of each trailer. Prior to the arrival of the test cattle to the slaughter facility, multiple 500-cm2 sponge samples were collected from the alleyways, pens, lead-up (“snake”), restrainer and roll-out belt. Once the cattle were harvested, samples were also collected from the hides and pre-evisceration carcasses. Prevalence, enumeration and PFGE tracking were conducted on all samples for E. coli O157:H7 and Salmonella.
On five of the six sampling occasions, both E. coli O157:H7 prevalence and load increased between sampling at the feedlot and sampling at the processing plant the following day. Salmonella prevalence and load on cattle hides increased for all sampling trips.
To determine the source of pathogens in the lairage environment, the researchers sampled potential external sources, including the transport trucks and the lairage environment. E. coli O157:H7 and Salmonella were detected in several truck samples and lairage environment samples. Several of the lairage environment sample sites had E. coli O157:H7 and Salmonella prevalence over 80 percent when averaged across all plants.
To determine if the lairage sites were sources of hide contamination, the researchers are currently analyzing E. coli O157:H7 and Salmonella isolates from the lairage environment, trucks, cattle hides and carcasses with pulsed field gel electrophoresis. More than 6,000 isolates are being examined.
Preliminary analysis revealed that 56 percent (141 of 252) of the cattle hide pathogen isolates were found to match PFGE types identified only in the lairage environment samples. There were no Salmonella isolates obtained from the feedlot or truck samples, however there were 255 Salmonella isolates obtained at the processing plant. The researchers concluded that since Salmonella was not present in the feedlot or truck samples, the Salmonella isolated from the cattle hides at the processing plant were transferred to the hides while the animals were in the lairage environment. The researchers determined that 95 percent (242 of 255) of the cattle hide Salmonella isolates matched PFGE type of isolates identified in the lairage environment samples. These findings further supported the conclusion that the pathogens were transferred in the lairage environment.
While data analysis is not yet complete for this project, preliminary conclusions support the need to further research the effect that lairage environments have on pathogen transfer in cattle presented for harvest.