Project title:     Factors affecting presence and spread of human bacterial pathogens in sheep on farms.

Duration:         January 1st 2000 to May 31st 2004

Background and Objectives

The outbreak of E. coli O157 infections in the human population of central Scotland in 1996 highlighted the importance of hygienic procedures in the meat production and processing chains.  Research has shown that the implementation of strategies such as a Hazard Analysis and Critical Control Point (HACCP) programme throughout production and processing can minimise the risks posed by food-borne pathogens. Despite this, and the efforts made by industry to implement HACCP, food-borne illness caused by zoonotic agents such as Campylobacter continues to increase in the UK.  Red meat and red meat-products have been implicated as likely vectors of foodborne illness.  To minimise the likelihood of zoonotic agents in raw meat, a HACCP approach for all stages of production required development and implementation.  However, an effective programme could only be designed once all of the hazards and their appropriate controls had been specified. 

Rationale and Objectives

The Meat Hygiene Service (MHS) set in place a scoring system to assess sheep cleanliness in 1997.  Following experimental work which demonstrated the relationship between visible sheep cleanliness and microbiological contamination of their carcases, the MHS system became standard practice across the UK.  MHS scores define sheep cleanliness using a five point scale.  However, contamination of the carcass is not only determined by the visible cleanliness of the animals.  There are indications that the spread of pathogenic bacteria through a population of sheep can also be influenced by diet and water supply.  The marketing and transport of sheep prior to slaughter represents a further stage where pathogenic bacteria may transfer between animals. The length of time spent in lairage is the final period in which bacteria may be spread between animals because there is evidence that ruminant faecal pathogens are present at the abattoir.  There was therefore a need to investigate whether the cleanliness of sheep on farms was directly related to their microbial status at the abattoir, and, if so, at which points between the farm gate and point of slaughter were the risks of contamination most increased. 

The purpose of this project was to examine if there was any influence by on-farm management practices, transport, marketing or lairage factors on MHS scores.  This information was required to determine if HACCP strategies could be developed to reduce the risk of carcass contamination with zoonotic agents.   A main objective of this project was to investigate if husbandry and handling factors influenced the bacterial contamination of sheep carcasses and whether there were any putative intervention measures which were likely to reduce this contamination

Approaches

Pathogen spread was mimicked using a harmless marker bacteria.  Representative samples were collected from statistically appropriate numbers of sheep by swab and faecal sampling.

 A number of farm factors were investigated to determine if they influenced carcass microbiology. These factors included: the effects of grazing marker bacteria-contaminated pasture and abrupt change of the feed offered to the stock.  The bacterial status of uninfected animals was monitored when they shared water troughs with marker-infected stock.  The effects of transporting sheep with dry or wet fleece was assessed, as was the role of mechanical ventilation during transport. 

 Livestock markets see high throughputs of transient animals and thus could potentially contribute to the spread of zoonotic agents between groups of sheep from different farms.  Spread of marker bacteria between groups was investigated at a simulated livestock market. The effects of breaking a transporter journey to the abattoir was investigated as was the effect of clipping of fleece prior to transport.  The survival of micro-organisms from lairage waste was examined in a laboratory-based experiment.  The role of specific lairage-related factors, such as clipping, amount of bedding used, the type of conveyer/restrainer and the post-stunning roll-out table in the spread of marker bacteria were investigated.

What it means and why it’s important

Pathogens associated with food-borne illness are present in UK sheep. Once infected, a single animal can be spread the infection through the rest of the flock.  Spread of infection occurs on farm, during transport, at livestock markets and in lairages at slaughterhouses.  We found that contaminated pastures and water troughs were also vectors for spread of infection between sheep.  Pathogens can survive for several weeks within livestock pens on farm and slaughterhouse lairages which highlights a need for thorough cleansing and disinfection of these environments between batches of livestock.  Transfer of marker from fleece to carcass during at slaughter was observed.  This study identified best practices and intervention measures that reduce the risk of fleece contamination prior to slaughter.  Reduced pathogen prevalence and levels on fleece is likely to correlate with a reduction in carcass contamination and, ultimately, microbiologically-safer meat products.