Incidence and Control of VTEC in Animal Feeds

The objectives of this study are to assess the levels and prevalence of verocytotoxic E. coli (VTEC) in domestic and imported animal feeds in order to determine any contribution of contaminated feeds to the increasing incidence of VTEC infections in UK livestock. Cattle, pig, sheep and poultry feeds will be studied because although VTEC have not been isolated from poultry in the UK, they have the potential to colonise birds. <P>

This study will commence with a full and comprehensive literature review of relevant papers and other publications. The purpose of the review will be to summarise our current knowledge of VTEC and, if required, shiga-like toxin-harbouring-phages (stx-harbouring phages) in feed ingredients, as well as factors which influence their survival during the commercial-processes used to manufacture finished feed. As part of this review, information will be gathered on the countries of origin and the amounts of imported and domestic feeds and feed ingredients used in the UK. <P>
The levels of verocytotoxic E. coli (VTEC), and verotoxin-gene-harbouring phages, associated with different imported and home produced feeds and feed components, will be determined by laboratory analyses of samples (250) of feed ingredients. Analyses will be by traditional microbiological culture methods as well as molecular-based techniques for direct detection of verotoxin (VT) genes. Samples will be collected using a statistically-weighted plan with sample assigned according to the amounts of feeds imported from specific countries or produced by UK farmers annually.
A laboratory study will be set up to mimic commercial manufacturing processes and a selection of VTEC-spiked feeds (250) will be analysed at various stages of compound feed production and storage to determine separately any effect of manufacture (heat, pressure and pelleting) on the survival of VTEC and stx-harbouring phages. In addition, any affect of storage interval of feed prior to sale will be investigated.
UK farms will visited and separate samples of concentrate feeds from unopened packages and hopper-stored feeds, together with forages, will be taken from farms in England, Scotland and Wales. In order to reduce costs to DEFRA, some samples will be taken by MAFF-trained ADAS samplers from farms of unknown VTEC status during the farm visits scheduled for FSA project B05003 (formally MAFF project FS3503- fate of pathogens in livestock manures). In addition, samples of trough feed will be taken from farms previously identified as VTEC-positive. These samples will be used to determine any incidence of on-farm contamination of feed by VTEC, and identify where contamination of feed is most likely to occur.
A final report will be written to advise DEFRA on the likely incidence of VTEC in imported and domestic animal feed and ingredients, and which will highlight any commercial processing stages that are effective in destroying VTEC or stx-harbouring phages in animal feeds. <P>
In order to ensure that the results of this work reach the agricultural community at large, technology transfer activities, including articles in the farming press and, with permission from DEFRA, a leaflet will be drafted for circulation to farmers which explains clearly the best practices to adopt which helps prevent on-farm contamination of feeds.

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To review current knowledge: Summarise information of the incidence of VTEC strains and stx-harbouring phages in imported animal feeds by undertaking a literature review of all relevant peer-reviewed scientific articles, guidance documents and other sources of information e.g. gathering information from contacts in the animal feed industry and from other research workers.
<LI> To assess the degree of contamination of imported feeds: Using information gathered as part of Objective 1, a statistically-weighted sampling plan will be developed. This will weight samples of imported and home produced concentrate feeds according to the amounts used and likely contamination with E. coli O157 and other VTEC strains, taking account of seasonal variations of concentrates and forage use. Analyses of the samples will assess the incidence and levels of E. coli O157 and other VTEC strains in different feed components from different sources by microbiological and molecular biological analyses. Samples of concentrate feeds will be collected predominantly from feed mills (for those ingredients used in the manufacture of compound feeds) and on-farm stores (for feeds fed directly to livestock).
<LI> To agree a sampling plan: A workshop will be held involving stakeholders to approve the sampling plan and agree the subsequent plan of the project.

<LI> To assess the potential effect of manufacture on the viability of E. coli O157 and other VTEC strains: A study will be undertaken in conjunction with a compound feed manufacturer where samples of feed and finished product will be collected at points along the manufacturing line. Samples will be subjected to the analyses described in paragraph 2 (above).

<LI> To assess the incidence of VTEC in farm-stored and trough-fed feeds: Many home-produced moist feeds are purchased and stored on farms prior to feeding. In some situations, the type of feed and the method of storing may be expected to facilitate the occurrence of VTEC. Feeds will be sampled on farms where these conditions are likely to be prevalent.

<LI> To assess the occurrence of VTEC in forages fed fresh on farms: In addition to sampling programme for concentrate feeds (described in paragraph 2 above), forage crops (e.g. fresh grass, maize and grass silage) which have been grown in fields fertilised by livestock manures will also be sampled. These samples will be used to determine any incidence of on-farm contamination of feed by VTEC, particularly as a result of the application of slurry and manure produced on the farm, to identify where contamination of feed is most likely to occur. A mini-silo study will be undertaken using both grass and forage maize to study the effects of ensiling on the presence of VTEC strains.

<LI> General technology transfer. With DEFRA permission, drafting of a leaflet for circulation jointly by DEFRA and ADAS to farmers which explains clearly the best practices to adopt to minimise on-farm contamination of feeds. In addition, after review by DEFRA project officers, papers and articles will be submitted to appropriate trade and scientific journals.
<LI> To produce a report for DEFRA. A final report will be produced for DEFRA. This will detail the results of the study and make recommendations.