Volume 3: The Early Years, 1986-88
3. Epidemiology
Changes in the production processes of MBM identified

3.42 Brokers were frequently used in the marketing of the products of rendering plants. Eighty per cent of MBM would be distributed within a radius of 100 miles, but the balance would go further afield. The industry representatives agreed to attempt to trace the source of feedstuff components that had been supplied to a number of farms that had experienced BSE. ¹

3.43 On 30 March 1988 Mr Andrews met with Mr Rees, Mr Cruickshank and Mr Bradley. Mr Rees said that it was:

more and more likely that the source of the disease lay in feedingstuffs and, in particular, in a combination of factors related to changes in procedures in the early 1980s. We were still investigating precisely what those procedures were and how they had altered. It was agreed that this work should be pursued vigorously regardless of what else was undertaken. It might be possible, by urgent action, to cut off the source of material for cattle . . . The industry was likely to be willing to follow a code of practice pending further legislation. ²

3.44 The investigations to which Mr Rees referred were being carried out by members of the Task Force led by Mr Peter Smith, a Senior Scientific Officer from the VIC in Preston. He produced an interim report on 28 March 1988 ³ and a further report on 27 April. ⁴ Mr Smith visited rendering plants with the objective of establishing what changes may have taken place in the feed industry to lead to the current problem. He was accompanied on some of these visits by Mr Meldrum and Mr Wilesmith. ⁵ He inspected 11 renderers and obtained data on 16 more, out of a total of some 58 plants in the United Kingdom. He reported:

. . . cooking times and temperatures are poorly recorded, inaccurate and in general do not provide the theoretical limits necessary to destroy the scrapie agent which can survive temperatures of 136°C for 18 minutes. ⁶

3.45 Mr Smith reported that, since 1980, there had been a change in the nature of the material being processed, for the following reasons:

(a) The sheep population has increased from approximately 22 million to 35 million resulting in more sheep material being processed.

(b) There has been a reduction in the number of operators (200 in 1960; 90 in 1980; 58 in 1988) resulting in more waste material being processed in fewer plants.

(c) Knacker's yards are thought to have decreased in numbers resulting in more casualty and condemned animals entering the rendering industry.

(d) The practice of skinning sheep heads and harvesting of sheep brains has almost ceased resulting in more whole unsplit heads going for rendering.

(e) There has been an increase in the number of cases of scrapie each year as measured through the VIDA II returns (1,083 extra flocks since 1980). In practice the number of actual cases which are unrecorded will be much higher. These casualty animals or slaughtered carcasses together with subclinical cases will end up in the rendering industry in increasing numbers. ⁷

3.46 Mr Smith also found the following changes in the processes used to produce tallow and MBM:

(a) Solvent extraction has almost disappeared: only two operators are thought to exist.

(b) Low temperature renderers have commenced operations.

(c) There has been a drift from batch cooking to continuous rendering in response to the needs for economy of scale to retain profit margins.

(d) Stord Bartz systems have been introduced which seem to operate at lower temperatures than Stork Duke systems.

(e) The continuous rendering systems will probably reach lower temperatures than batch rendering due to continuous movement of material in the cooker and displacement with cold raw material. ⁸

3.47 His conclusions were as follows:

The rendering industry operates with processes which with few exceptions are inadequate to destroy scrapie agent. This together with increasing amounts of sheep material consisting of whole carcasses and heads which undoubtedly contain increasing numbers of scrapie cases may have resulted in contaminated tallow and meat and bone meal reaching the animal feed compound industry.

Scrapie contaminated material has probably always entered and survived the rendering process but only in small amounts prior to 1980. With the change to continuous rendering large volumes of contaminated products have been introduced to the food chain.

It is not possible to say what the critical limit is for agent relative to final feed concentration necessary to cause infection. Equally it is not possible to say with certainty which plants may be responsible for the present problem but it would seem likely to be one operating in the South West or South East due to the usual practice of distributing finished product mainly to the local area. These geographical areas are those which are prominent in the number of cases of BSE. Further dissemination of finished product will obviously occur but only on a limited scale. ⁹