Project title:    Source and spread of particulate and bacterial contamination between cattle during the farm to abattoir phase of production

Duration:         October 1st 1999 to 30th September 2002

Background and purpose

Research has shown that the implementation of hazard control schemes such as HACCP (Hazard Analysis and Critical Control Point) programmes throughout meat production and processing can minimise the risk of pathogens on raw meat.  Although industry has begun to implement such schemes, food-borne illness caused by zoonotic agents such as E. coli O157 and Campylobacter continues to increase and red meat is often implicated as a primary source of infection.  Farms, livestock markets, transport and the abattoir environment are likely place where contamination with E. coli O157, Salmonella or Campylobacter could happen.  The purpose of this study was to identify and characterise common vectors of beef cattle contamination in these areas so that appropriate control measures could be developed.

Specific objectives 

Results

E. coli O157, Salmonella and Campylobacter incidence in beef cattle on farms in England/Wales and Scotland were investigated by the collection of faecal samples in both the autumn and spring seasons.  E. coli O157 prevalence was 4% overall, but was higher in Scotland than England/Wales.  This result was statistically significant. 

Campylobacter spp prevalence was 18% overall, and again the prevalence was significantly higher in Scotland.  Salmonella spp. prevalence were very low in both regions and averaged <0.2%.

From information collected via a questionnaire, the risk factors that were associated with increased pathogen prevalence on-farm were:

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The spread of visible and bacterial contamination between cattle during transport was investigated in two stages.  The first involved mixing clean and dirty animals in transport, and highlighted a considerable increase in visible dirtiness of clean cattle after transportation with dirty cattle.  A significant increase in bacterial levels was detected on wet animals following a period of rainfall (0.2 and 1.2 mm/hr during loading and unloading from the transporters). 

Overall higher bacterial numbers were detected on dirty cattle, with the brisket or midline consistently the most-heavily contaminated part of the animal.  The second stage investigated the effect of the dry matter content of the diet that stock were fed (25%, 55%, 85% w/v dry matter content) and how this influenced cattle cleanliness after a 2.5 hour period of transport.  Overall cattle that were fed low dry matter diets, such as silage, were visibly cleaner both pre- and post-transport and had the lowest levels of both bacteria when compared to cattle fed on higher dry matter diets.  Numbers of bacteria were significantly higher in autumn than the summer.

To establish the incidence of contamination in cattle, and investigate bacterial spread between cattle in a livestock market environment, a survey was carried out of 6 livestock markets, which were visited during both the summer and winter seasons.  E. coli O157 was present in 0.9% of pre-sale samples and 1.4% post-sale samples, Campylobacter was present in 8% of samples overall and Salmonella was not detected. 

Higher bacterial levels were associated with:

A simulated market experiment used harmless marker bacteria to mimic pathogen spread through a typical livestock market.  The results of this study showed that the market environment provided significant opportunities for the transfer of pathogens between animals.  Direct transfer of marker bacteria between animals was observed between 33%, 17% and 47% of animals in a group during three separate experiments.  Marker was also transferred from animals to environmental surfaces such as race rail surfaces.  Environmental transfer was widespread because up to 89% of the surfaces sampled were positive for the marker organisms.  Furthermore, transfer was higher in confined areas such as races and crushes where the risk of transfer from cattle hide would have been greater.  The introduction of unfamiliar animals also increased the potential for transfer of marker. 

The growth and survival of E. coli O157, Salmonella spp., and Campylobacter spp., on metal, painted metal, concrete straw and hide, surfaces commonly found in the cattle lairage, were investigated under warm or cold, wet or dry and clean or dirty conditions.  The conditions investigated were selected from a range commonly associated with abattoirs.  Pathogen survival was better in dirty samples (faeces) and on straw or hide, than on metal or concrete.  Survival was also better in cold (10^oC) than warm (25^oC) conditions, and at higher levels of relative humidity (96% RH).  Survival of pathogens was shown to exceed 24 hours under these conditions, meaning a high risk for cross contamination between animals processed on different days.

A ‘best’ and ‘worst’ practice comparison was carried out.  ‘Best’ practice animals were transported for a single 2.5 hour journey after which the levels of bacteria on hide had increased.  There was no significant difference in bacterial levels on the hide of the ‘worst’ practice animals after a short journey of 1 hour.  However, following a 2 hour period of penning. the level of bacteria on the hide rose between 0.2-0.5 log CFU cm^-2.  Bacterial levels subsequently fell following mixing with unfamiliar animals in a strong sunlight, high temperatures, in the outdoor environment, but rose again (range 0.25-1.0 log CFU cm^-2) following a further 2.5 hours in transport.

Results obtained from this study were developed to identify intervention strategies, which could be used as the basis of a hazard analysis and critical control point (HACCP)-type programme for the farm-to-abattoir phase of the production cycle.  A generic Hazard Analysis and Critical Control Point (HACCP)-type scheme was produced that included the development of a flow chart for beef production, which included all of the main UK production systems for beef cattle.  Processes and steps of the production cycle (e.g. birth, arrival, suckling, weaning/housing, grazing, finishing, transfer/transport, slaughter) were identified, and the associated risks and hazards were categorised.  A summary sheet was produced that included an outline of general good hygiene practices, identification of control measures, their limits, and appropriate monitoring procedures.  A description of what corrective actions should be followed to restore control to the production system when problems occurred and effective recording procedures were also documented.

What it means and why it is important

These investigations have provided evidence that beef cattle contamination by zoonotic agents represents a credible risk to food safety.  Movement of animals and environmentally-mediated transfer from animal-to-animal are effective ways to spread contamination between beef cattle.  Pathogens can survive within environments such as lairages for more than 24 hours, and thus the environment can be a reservoir of zoonotic agents.   The risk of transfer of pathogens to a carcass from cattle hide contaminated is high.  There are measures such as lowering cattle movement, keeping cattle dry and keeping animals in lairage for as short a time as possible which can reduce carcass contamination with zoonotic agents.  Adoption of the best practices identified by this study will lower the likelihood that meat and meat products are contaminated with zoonotic agents.

Project publications (click here to request a paper from the authors by email)

Collis, V. J., Reid, C. -A., Hutchison, M. L., Davies, M. H., Wheeler, K. P. A., Small, A. and Buncic, S. 2004. Spread of marker bacteria from the hides of cattle in a simulated livestock market and at an abattoir.  J. Food Prot. 67:2397-2402.

 Avery, S. M., Liebana, E., Hutchison, M. L. and Buncic, S. 2004.  Pulsed field gel electrophoresis of related Escherichia coli O157 isolates associated with beef cattle and comparison with unrelated isolates from animals, meats and humans. Int. J. Food. Microbiol. 92:161-169.