M01015: Factors affecting the presence and spread of human bacterial pathogens in sheep

Study Duration: January 2001 to February 2004

Contractor: ADAS Consulting Ltd

The project aims to characterise the spread of contamination with food-borne pathogens at various points along the lamb production chain and evaluate intervention methods to control that spread. The effects of on-farm management practices as well as transport, marketing and lairage factors, on both MHS clean livestock category and microbiological contamination, are being examined to clarify the present knowledge base. The project plans to produce a HACCP based approach to the farm to abattoir production of sheep meat.

The project was carried out to determine the spread of bacterial species between sheep along the production/processing chain, and to develop intervention measures to reduce risk. Management (i) on-farm, (ii) during transport, (iii) marketing and (iv) lairage were investigated for their individual and combined influence on sheep cleanliness and carcass contamination.

Farm factors examined included the effects from grazing on contaminated pasture, and the role of shared water sources. Key findings were:

• Grazing on contaminated pasture was shown to pose a significant risk for pathogen transfer to sheep and lambs.
• Contaminated water sources and horizontal transmission from direct contact with contaminated animals increases the risk of individual animal contamination with foodborne pathogens.

Transport factors examined included the effects of transporting sheep in a dry or wet fleece condition on the within-pen and between-pen spread of bacteria, and the use of mechanical ventilation as an intervention measure. Key findings were:

• Wet sheep, compared with dry sheep, increased the spread of external animal 'marker' bacteria (Ps. fluorescens) within the pen, and environmental 'marker' bacteria (E. coli W18) from the sides of pens. Cross-contamination occurred within the pen and to sheep in other pens.
• Cross-contamination under mechanical, as opposed to natural ventilation conditions was generally worse and, as such, cannot be justified as a way of reducing microbial cross-contamination during transport.

Market factors assessed included the effects of breaking the journey (unloading and reloading) to the abattoir with both clipped and unclipped sheep. Also, the effects of moving and penning of sheep and their close confinement within the market environment was studied. Key findings were:

• The spread of 'marker' bacteria was greater in lambs during the broken journey treatment than for those transported on a 'direct' journey. It is thought that the extra movement of animals to unload at market and reload for slaughter provides extra opportunity for contamination.
• Belly and rump clipping in this experiment did not significantly influence the spread of marker bacteria. In practice clipping is used to improve the visual cleanliness of 'dirty' sheep presented for slaughter.
• Wet sheep, compared with dry sheep, increased the spread of 'marker' bacteria in the market environment. Because carcass contamination is linked to fleece contamination, this finding has major implications for carcass contamination.

Lairage factors studied included the role of clipping, bedding, the conveyer/restrainer and the post-stunning roll-out table, in the spread of bacteria. The survival of pathogens on materials collected from sheep lairages were also investigated. Key findings were:

• The foodborne pathogens studied, Campylobacter fetus, Salmonella spp. and E. coli O157, were able to survive for long periods of time on surfaces commonly found within sheep lairages. This emphasises the need for regular and thorough cleaning and disinfection of lairages to prevent potentially pathogenic organisms contaminating the fleeces and resulting carcasses of previously clean sheep.
• Of the lairage factors studied, the use of clean bedding and disinfection of the roll-out table were the most effective at reducing the spread of bacteria from contaminated animals within the lairage environment.

Intervention measures, which brought together the most significant factors influencing sheep hygiene, were quantified within each of the three discrete phases (i) during transport, (ii) in livestock markets and (iii) in lairages.

• In transport; straw diets on the farm, dry sheep, adequate straw bedding, loading and unloading quietly and short journey time reduced the level of bacterial contamination on the fleece and on the carcass.
• During the market phase; straw diets on the farm, an under cover market (i.e. dry sheep), a short time in market and no animal mixing led to a lower level of fleece contamination.
• During lairage and slaughter; straw diets on the farm, lairaging in clean straw-bedded pens, a short time in lairage and disinfection of the conveyor and roll-out table reduced the spread of marker bacteria onto the fleece and resulting carcass.
• Reductions in bacterial contamination were generally greater on the fleece than the carcass. Cross-contamination at the dressing stage is thought to prevent the full impact of lower positive fleece numbers from becoming lower positive carcass numbers.
• In each phase, the environmental marker was found in greater numbers on the fleece and carcass than the external animal marker. This emphasises the need for periodic cleansing and disinfecting of all surfaces that sheep are likely to come into contact with.

A validation of intervention measures from all three phases was performed on lambs, which were slaughtered in a commercial abattoir. Key findings were:

• The culmination of intervention measures resulted in a reduction in environmental 'marker' by 42% and 92% on the fleece and carcass respectively.
• Interventions employed earlier in the process (during market and transport phases) may reduce the number of contaminated fleeces more effectively than interventions applied during the lairage phase.

Overall, implementing intervention measures from farm to slaughter has the potential to markedly reduce the spread of bacterial contamination to the carcass. This could have important implications for consumers through reducing the risk of food-borne illness both from eating meat and from cross contamination from raw meat to other ready to eat foods during preparation.

The results generated by this project have been used to generate key messages which have been promoted to the meat industry as 'best practice' for the production of clean sheep for slaughter.

Publications

Hedges, V.J., Deakin, D., Hutchinson, M and Davies, M.H. (2002). Factors affecting the meat hygiene scores of sheep arriving at abattoir and the subsequent bacterial carcass contamination. Proceedings of the 48th International Congress of Meat Science and Technology, pp926-927.

Small A., C-A. Reid and S. Buncic (2003). Survey of Conditions in Lairages at Abattoirs in South West of England and in vitro Assessment of the fate of Escherichia coli O157, Salmonella Kedougou, and Camplyobacter jejuni on Lairage-related Substrates. Journal of Food Protection, 66, 1750-1755.

Avery, S.M. & Buncic, S. (2003). In vitro assessment of survival-, growth- and toxin production-related diversity of E.coli O157 and potential implications for meat safety. VTEC Conference 2003, Edinburgh, June 8-11, p. 28.

Collis, V. J., C.-A. Reid, D. Tinker, M. L. Hutchison, M. H. Davies, K. P. A. Wheeler, A. Small, P. J. Hadley and S. Buncic (2004). Best practice interventions on-farm, at the livestock market and during lairage to produce microbiologically cleaner sheep for slaughter. European Union Risk Analysis Information Network (EU-RAIN), Farm to Fork Food Safety - A Call for Common Sense Conference Centre of the National Bank of Greece, 41-43 Posidonos Avenue, Glyfada, Athens, Greece, May 12th-14th 2004.

Final Report

The final report is available from the Agency's Information Centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency, tel: 020 7276 8181/8182, email: infocentre@foodstandards.gsi.gov.uk

Contact: For any enquiries concerning this research project, please contact the relevant Programme contact or email: science@foodstandards.gsi.gov.uk