B05008: The levels of pathogens in abattoir wastes

Study Duration: November 1999 to May 2002

Contractor: University of Bristol

Abattoir wastes permitted to be spread on land fall into several categories: gut contents, blood, lairage waste and liquid from washing processes. The initial levels of pathogens in some of these wastes are likely to be high and may present a hazard to human health. Before disposal, wastes are stored for a variable period of time, under varying conditions. It is unclear whether this leads to increase or decrease in the number of pathogens and therefore under what circumstances storage may increase or decrease the potential hazard. Storage and different storage conditions may affect different pathogens in different ways. The proposed research will therefore examine the prevalence of the major foodborne pathogens in abattoir waste destined for disposal on agricultural land. This will allow the formulation of policies on control of waste disposal based on a clear view of the risks from the prevalence of specific pathogens.

The research approach is to survey current commercial practice and then to select representative commercial sites to sample for pathogens present in the waste.

Objective 1
A literature search, based on a combination of traditional and electronic information retrieval systems, will be carried out to ensure that the project is founded on the most up-to-date information. A network of world wide contacts with research groups working on abattoir waste topics will also be established.

Objective 2
Using the DFAS and School of Veterinary Science database of abattoirs, a representative selection of up to 30 plants will be surveyed for the different types of waste spread on land, the quantities stored, the times and conditions of storage, the timings, quantities and methods of application and the types of land on which it is applied. Those chosen will include both large and small plants and red meat and poultry processing units. The survey will be carried out by personal visit, inspection and interview.

Objective 3
Methods for isolation/enumeration of the microbial pathogens will be developed in collaboration with the Centre for Applied Microbiology & Research (CAMR), while those for the protozoan parasites will be developed in collaboration with Thames Water (Reading). The methods selected will be validated using various types of abattoir wastes artificially inoculated with a range of levels of pathogens.

Objective 4
A survey of the pathogens in commercially produced abattoir waste will be carried out by selecting abattoirs disposing of different types of waste (identified in Objective 2), collecting a representative number of samples and examining them for the presence of foodborne pathogens. The sampling plan will include four seasons and various geographical locations. An initial working plan for the survey is based on our preliminary discussions with the industry, which have identified seven types of abattoir waste spread on agricultural land. The wastes presently spread on land, broken down by species are:

Cattle: lairage waste, rumen contents
Sheep: lairage waste, rumen contents
Pigs: stomach contents, gut contents, blood

However, it should be kept in mind that a) the types of wastes that are eventually targeted by the survey, b) the types of pathogens targeted within each type of waste, c) the number of abattoirs included in this survey and d) the number of samples for each type of waste, will only be chosen after completion of Objectives 1 & 2.

The above also applies to poultry abattoir wastes, although there are reasons to believe that at present poultry wastes are generally rendered and are not spread onto land.

The results indicated that the overall incidence of bacterial pathogens found in abattoir wastes was low. Salmonella and E. coli O157 were not isolated from any of the abattoir waste samples tested. The overall incidence of the most commonly isolated pathogen, campylobacter, was 5.7%. Listeria monocytogenes was found in only 1.1% of all samples. However, when only the most common and most contaminated waste type, lairage-based waste, was considered, the incidence of these pathogens was higher.

Possible explanations for this low incidence of bacterial pathogens include low prevalence in slaughtered animals; a 'diluting' effect of mixing contaminated wastes with non-contaminated wastes (e.g. blood) and/or water; increased use of disinfectants at abattoirs during the course of the study; and potential pathogens dying-off during waste storage.

Giardia and crytosporidium were not examined in samples collected from poultry-only abattoirs. In wastes from red meat abattoirs, the overall incidence of giardia and cryptosporidium was relatively high - around 50 and 40%, respectively. The protozoans were found most frequently in lairage-type waste, followed by effluent-type waste. When only lairage wastes from single-species abattoirs (one abattoir per species) were considered, the incidences of giardia and cryptosporidium were higher at sheep and pig abattoirs than at the cattle abattoir. Also, the incidences of both protozoan pathogens in lairage wastes at three-species abattoirs were higher as the throughput was higher, and vice versa. The sampling season did not significantly affect either overall incidences of giardia or cryptosporidium or their average total counts/gram in abattoir wastes.

This study showed that no defined and standardised system for handling wastes at abattoirs exists, although waste management at poultry abattoirs is much more uniform compared with red meat abattoirs. It could be assumed that, from abattoir and meat hygiene perspectives, waste materials (potentially or actually containing pathogens) should not be stored at abattoir premises. On the other hand, from the agricultural land safety aspect, they should be stored at abattoirs as long as possible - to achieve maximum reduction of pathogens before disposal on land. To put these opposing interests in balance, pathogen time/survival rates during abattoir storage should be compared with those on land. To achieve that, further research on the fate of pathogens during waste storage at abattoirs is required. If wastes are to be stored at abattoirs, further research on storage conditions, potential treatments to reduce/eliminate pathogens, and appropriate checks and monitoring mechanisms is required.

Final report is available from the FSA Library and Information centre.
To obtain a copy, please contact the Enquiry Desk, Dr. Elsie Widdowson Library and Information Services, Food Standards Agency (020 7276 8181/8182 or at library&info@foodstandards.gsi.gov.uk).

A peer review article on this project can be found in Food Protection Trends, Vol.23 No.4, 315-325. Titled 'Potential for spread of some bacterial and protozoan pathogens via abattoir wastes applied to land'.

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