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

Project Code: M01015

30/06/2004

ADAS Rosemaund
Collis, V ; Davies, M;
Direct Laboratories Ltd
Hutchison, M;
Division of Farm Animal Science, Department of Clinical Veterinary Science, University of Bristol,
Buncic, S; Reid, C; Small, A;
Silsoe Research Institute
Tinker, D;
British Leather Confederation
Hadley, P

Background and introduction

1. Sheep have been identified as a major source of VTEC, including E.coli 0157, and also harbour other pathogenic bacteria such as Salmonella and Campylobacter. Reducing
the incidence of these pathogens in the faeces and fleeces of sheep presented for slaughter will have a direct impact on their incidence in retailed meat products.

2. The overall objective of this project was to investigate factors that influence the presence of human bacterial pathogens in the particulate and bacterial load of sheep from the farm to the point of slaughter.

Use of marker bacteria

3. The spread of pathogens was assessed through the use of harmless ‘marker’ bacteria and a representative sample of sheep in parts of the project were also swab and faecal
sampled for the assessment of pathogenic bacteria including E.coli 0157, Salmonella and Campylobacter.

4. For an ‘internal’ marker, a pilot study showed that discrete feeding of experiment animals twice daily is recommended in order to produce a consistent shedding pattern of
the marker organism in the faeces of sheep. Results showed that sheep fed marker ‘discretely’ on an indoor silage diet will consistently shed marker from Day 3 following the commencement of marker feeding. However to ensure that consistency of shedding was always achieved, a standard 5-day introductory dosing regime for the internal marker (E. coli K12) was adopted.

5. When using an ‘external’ marker, a pilot study demonstrated that the paint-brush technique was best method for the application of harmless marker bacteria to the fleece of sheep (Pseudomonas fluorescens). A similar paint-brush technique or a spray application was effective for the application of marker bacteria (E. coli W18 and E. coli A55) to environmental surfaces. For the recovery of marker bacteria from fleeces, the wet sponge method with a whole side or whole belly swabbing method was the chosen technique. It is important that methods are both effective and practically efficient.

Farm factors

6. In Objective 1, the farm factors examined included the effects from grazing contaminated pasture and changing the sheep’s diet, and the role of shared water sources, in the spread of bacteria from animal to animal.

7. The results show that contaminated pasture poses a significant risk for pathogen transfer to sheep and lambs. It is therefore important to consider management programmes to
ensure that sheep destined for slaughter are not exposed to potentially contaminated pasture during the period leading up to slaughter.

8. A contaminated water source and horizontal transmission from direct contact with contaminated animals, increases the risk of individual animal contamination with foodborne
pathogens.

9. It is concluded that these two factors should be considered in any management programme when aiming to minimise the risk of pathogen transfer between individuals and groups of sheep, particularly just prior to slaughter.

Transport factors

10. In Objective 2, the effects of transporting sheep in a dry or wet fleece condition on the within-pen and between-pen spread of bacteria was assessed, and the use of mechanical
ventilation as an intervention measure was tested.

11. Wet sheep, compared to dry sheep, generally increased the spread of external animal micro-organisms (Ps. fluorescens) within the pen, and for environmental microorganisms
(E. coli W18) from the sides of pens, there was cross-contamination both within the pen and to sheep in other pens.

12. Cross-contamination under mechanical, as opposed to natural ventilation conditions was generally worse. Therefore mechanically ventilated systems cannot yet be justified as a way of reducing microbial cross-contamination during transport.

Market factors

13. In Objective 3, the effects of breaking the journey to the abattoir was investigated with clipped and unclipped sheep. In a separate experiment, the effects of moving and penning of sheep and their close confinement within the market environment was also assessed.

14. Bacteria applied to the fleece of marked lambs were isolated from a higher proportion of lambs in the broken journey treatment than for those transported on a ‘direct’ journey. The extra movement of animals to unload at market and reload for slaughter, provides extra opportunity for contamination.

15. Belly and rump clipping in this experiment did not significantly influence the spread of marker bacteria. However in practice clipping is used to improve visual cleanliness of sheep if there is contamination of the fleece, and indeed many abattoirs now insist on belly clipping when lambs are in full fleece and during the winter months.

16. In the market environment, where sheep are in close proximity to each other, the results showed clearly that sheep with wet fleeces are more likely to spread and transfer contamination to other sheep. Because carcass contamination is linked to fleece contamination, this finding has major implications for carcass cleanliness.

Lairage factors

17. In Objective 4, the survival of micro-organisms under lairage conditions was critically examined in a laboratory experiment, using materials collected from sheep lairages. In a separate experiment, the role of specific lairaging factors, such as clipping, bedding, the conveyer/restrainer and the post-stunning roll-out table, in the spread of bacteria were investigated.

18. The three food-borne 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. Therefore if lairages are not cleaned and disinfected thoroughly on a regular basis, there is the potential for these organisms to contaminate the fleece and also the resulting carcass of previously clean sheep.

19. Of the lairage factors studied, the results indicated that 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

20. Aspects of sheep production investigated in Objectives 2, 3 and 4 identified single factors that had a significant influence on the hygiene aspects of sheep. In Objective 5, the most significant of these singular interventions were brought together and their effects quantified within each of the three discrete phases from farm-to-abattoir, i.e. during transport, in livestock markets and in lairages.

21. In transport, the results indicated that the intervention measures applied (straw diet onfarm, dry sheep, adequate straw bedding, load/unload quietly, short journey) reduced the level of contamination, on the fleece and on the carcass, from both the environmental marker (E. coli W18) and the fleece marker (Ps. fluorescens).

22. During the market phase, adopting intervention measures (straw diet on-farm, under cover market (i.e. dry sheep), short time in market, no animal mixing) for animals destined to go through the livestock market led to a lower proportion of fleece contamination from both markers, and lower levels of the environmental marker on the carcass, but not of the animal marker.

23. During lairage and slaughter, the intervention steps employed (straw diet on-farm, lairaged in clean straw-bedded pen, short time in lairage, disinfection of conveyor and toll-out table) reduced the spread of both marker bacteria onto the fleece immediately before slaughter, and subsequently onto the resulting carcass for the environmental marker, but not the animal marker.

24. The reduction in contamination effect was generally greater on the fleece than the carcass, indicating that cross-contamination occurs during the dressing process which prevents the full impact of the lower positive fleece numbers from becoming lower positive carcass numbers. This was supported by the HACCP counts which generally indicated no consistent effect between intervention and non-intervention lambs for both TVC and Enterobacteriaceae counts.

25. In each phase, the environmental marker was found in greater numbers on both the fleece and carcass than the external animal maker. This emphasises the need for thoroughness of cleansing and disinfecting of all surfaces that sheep are likely to come into contact with.

Validation in a commercial abattoir

26. The various intervention measures tested in Objective 5 in the three discrete phases were brought together and evaluated as a whole system in Objective 7, and lambs were
slaughtered in a commercial abattoir, with both their fleeces post-stunning and their carcasses assessed for marker bacteria contamination.

27. Overall, the implementation of intervention measures during all three phases culminated in a reduction in contamination from the environmental marker by 42% and 92% on the
fleece and carcass respectively. No such assessment of the animal marker could be made because of a failure to recover it from lamb swabs taken on the intervention day.

28. There is an indication that interventions employed earlier in the process (during market and transport phases) may reduce the number of contaminated fleeces, whether from
environmental or animal markers, more effectively than interventions applied later during the lairage phase.

29. The impact of the intervention measures was not consistent for the animal marker, although the reduction in the number of carcasses contaminated by the environmental
marker was considerable.

30. Implementing intervention measures throughout the production chain, in all three phases up to slaughter, has the potential to markedly reduce the spread of environmental contamination to the carcass. This could have important implications for meat-eating consumers through reducing the risk of food-borne illness.

HACCP

31. The findings from the various project objectives were interpreted and developed into a HACCP type document for sheep production (Objective 6).

32. The guidance provided by the document produced ‘On-farm meat hygiene based on HACCP principles’ will assist sheep producers, livestock markets and lairages in their quest to reduce the risk of contamination transfer. Adopting as many of the best practice intervention measures outlined will significantly reduce the risk of human foodborne pathogens entering the food chain via sheep products. Wet hides (and fleeces)

33. Fleece moistures assessed in Objective 5 were greater at slaughter for those lambs subjected to simulated rainfall at the pre-market or pre-transport point in the production
chain. This can have significant implications on the spread or transfer of contamination, as shown in Objective 3 of this project, and also in project M01009 with beef cattle.

Because the cause of this increased detection of bacteria from wet/damp hides or fleeces was unknown, this was investigated in more detail with cattle hides in a laboratory
experiment (Objective 8).

34. Both E. coli and Enterobacteriaceae was recovered in greater numbers; 2.9 and 5.9 times higher respectively, from wetted hides than from dry hides, but there was no difference in the counts for TVC. The higher detection levels was because a higher proportion of the bacterial load was recovered by a single swab pass from wetted hides. This has major implications on contamination transfer and meat hygiene, and producers, hauliers, auctioneers and abattoir managers must be aware of the importance of keeping animals dry during the pre-slaughter stage.

Future work

35. It is suggested that the following topic areas merit further research investigation or knowledge transfer effort ;-
· Evaluation of livestock cleanliness and meat hygiene issues related to novel livestock systems, e.g. in wood chip corrals, is needed.
· The clipping of lambs pre-slaughter is widely practised, but there is little critical microbiological information available on the effectiveness of this procedure.
· There is a need to fully investigate and provide better information on effective cleaning and disinfection of livestock transporters.
· The potential of novel post-stunning techniques for improving the microbiological cleanliness of cattle and sheep carcases should be evaluated.
· There is a need to develop automated disinfection equipment for use at critical points in abattoirs, e.g. at post-stun/roll out point.
· The implementation of the new Hygiene Regulations to the whole meat production chain should be supported by detailed guidance to enable producers and others to complete a Food Safety Management System for their individual units.
· A continual knowledge transfer effort should be maintained to promote ‘clean livestock’ at future key beef and sheep events, in order to maximise the uptake from research funding to date.

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