Volume 5: Animal Health, 1989-96
2. The ruminant feed ban, 1989-96
Cross-contamination in feedmills
Avoidance of cross-contamination in feedmills

2.45 In vol. 3: The Early Years, 1986-88 we concluded that once pipeline stocks of ruminant feed containing MBM had been consumed, cross-contamination in feedmills was the principal reason why cattle continued to be infected with BSE.

2.46 The chronological account later in this chapter sets out the evidence that suggests this was so, and describes how it was not until 1994 that MAFF and the feed industry became aware of the problem. In this section we set out the evidence we have received about the industry's awareness of general cross-contamination difficulties in feedmills prior to the RFB's implementation.

Avoidance of cross-contamination in feedmills

2.47 Feedmills have been aware for decades of the risk of cross-contamination between batches of feed intended for different species. UKASTA has suggested that 'the reasons for cross-contamination occurring in a feed milling process are simple, obvious and have been well understood since the early days of the modern feed compounding industry'. ¹ Mr James Crawford, former Chairman of UKASTA's Feed Executive, described the types of cross-contamination possible in feedmills:

• Because compound milling plant is not completely self cleaning each raw material transported along a common conveyer system will leave microscopic traces which will be picked up by the next raw material conveyed. Similarly a blended batch of feed will leave microscopic traces which will be picked up by the next batch in the system. If a batch of dairy compound follows a batch of pig compound, microscopic traces of the raw materials in the pig compound could be found in the dairy compound. Prior to BSE this low level contamination was considered a problem only when drugs were being incorporated.

Macro as well as micro levels of contamination can take place in feedmills.

• Raw materials can adhere to the sides of bins and conveyers and build up sizeable agglomerations. In time these agglomerations can fall into the stream of material and may corrupt a formulation.
• Slides on bin tops or bottoms do not always open and close perfectly e.g. a slide which is stuck partially open may leak a particular raw material into formulations into which that material is not programmed.
• Formulators can make mistakes.
• The software in a feed mill which controls weighing and blending can be corrupted for various reasons.
• At the point of intake a material can be consigned to the wrong bin resulting in an unplanned mixture of raw materials.
• Raw materials which were themselves semi-products containing a number of component raw materials were on sale to compounders and were bought because they appeared to be cheap sources of nutrients. The manufacturers of these semi-compounds were sometimes less than open about their ingredients.
• Contamination of one raw material with another may take place in importers' stores.
• Unplanned mixtures of finished products may occur in feedmills and may be delivered to farms.
• Weighbridgemen may consign a product to the wrong compartment of a bulk delivery truck resulting in delivery of the wrong product to the farm.
• Drivers of bulk delivery trucks may mix up their deliveries. ²

2.48 Though compounders devised procedures to help avoid these risks, the nature of the feed manufacturing process made it impossible to avoid the risks completely. ³ Up to the late 1980s, steps taken to avoid cross-contamination mainly revolved around the need, under the Medicines Act 1968, to avoid the accidental inclusion of medicines or other additives in the wrong product. Careful scheduling of production was the main tool used to achieve this. Suitable gaps would be left in the production process to ensure, for example, that a ruminant ration was not manufactured immediately following a monogastric ration that contained medical additives. ⁴

2.49 UKASTA issued a Code of Practice on Cross Contamination in Animal Feedingstuffs Manufacture in 1982. Companies either adhered to this Code, or their own codes based on the UKASTA code. ⁵

2.50 We now turn to examine events following the introduction of the ban, which necessarily revolve around the discovery of BSE in calves born after the ban (BABs).