17 JUNE 2010.

Drayton Farm Risk Assessment

The Committee was presented with a Risk Assessment prepared by the Veterinary Laboratories Agency, which assesses the residual TSE risk at Drayton Farm due to the presence of experimental animals and field cases on the site, and the land spreading of composted manure and wastewater. SEAC last considered this issue at its 53rd Meeting on 21-22 September 1998.

Several Members commented that the methodology of the Risk Assessment was sound. However,concerns were raised that some of the specific input values to the risk assessment are problematic because of the large number of assumptions on which these are based.

A Member suggested that the outputs of the Risk Assessment needed to be checked against the available data to ascertain whether these were consistent. For example, there are data from Iceland and the Ripley flock which clearly show that there is a risk from re-introducing livestock onto land which has previously held a scrapie infected flock. This should have raised questions in the minds of the authors about why the model comes out with a very low risk.

Additionally, a Member suggested that more consideration should be given to whether the theoretical assumptions based on regulations, actually correlate with the real life activity on the farm.

A Member noted that the Risk Assessment adds little to SEAC’s previous advice on this issue provided in 1998, and the Chair stated that because there are no additional data available, it is difficult for SEAC to update its previous advice on this issue.

The Committee agreed that:

  • The methodology of the Risk Assessment is sound; however:
  • there are serious problems withthe input assumption to the model, given the lack of data;
  • The outputs of the model are therefore uncertain; and
  • There is no need to revise SEAC’s advice of21-22 September 1998.

Extract from Minutes of SEAC 53, 21/22 September 1998.

Item 9 - Disposal of excreta from cattle experimentally infected with BSE (paper SEAC 53/6)

42.The Committee had previously considered options for disposal of waste from cattle exposed to BSE in January 1998. Members had before them paper SEAC 53/6 providing details of possible disposal options for excreta from two long term experiments which were starting at Drayton Experimental Husbandry Farm. Alternative measures to incineration had been examined due to the practical and cost problems of pursuing this option for such a long period. Further information about the farm and methods of disposal which would comply with Good Agricultural Practice were provided. The key change was the proposal to utilise crops from the farm and the Committee were asked to note the concerns of a neighbouring farmer with a watercourse on his property which ran through the experimental farm about possible run off.

43.The Committee noted that the animals were being held in brand new buildings and that there were arrangements for separation of solid and liquid waste. The housing arrangements and husbandry procedures would ensure rigorous separation of the different groups of animals. It was reported that the Committee’s views would be applied to disposal arrangements for excreta from the sheep experimentally exposed to BSE at the Institute for Animal Health.

44.The Committee confirmed their previous advice that the waste from challenged animals should be incinerated for the first 28 days (which represented an extended “safe” clearance time from cattle intestines) and that, thereafter, the excreta should be composted for one year. They agreed that there was no scientific basis why composted material should not be spread on land as fertiliser prior to planting crops which could then be used for human consumption or animal feed, although coppicing may present the most desirable option from the point of view of public perception. However, the Committee felt it would be prudent not to spread the material on pasture which would be grazed by cattle, and that the experimental animals which were part of the cattle bioassay experiment should not be given the food from the farm. This was in order to prevent any future challenge of a positive result that contaminated food may have been a route of exposure which might lead to a consequent claim that the tissue being assayed was not really positive.

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