FBA Issue 5: November / December 2005
Pathogen control in feed mills
by Jon RATCLIFF
GOOD quality feed is about careful selection of raw materials, not just nutritional values and specifications. Raw materials need to be carefully sourced, managed and stored to avoid risk of bacterial contamination. Most raw materials are grown, harvested, processed and transported independently of the feed industry. Many ingredients are often handled up to 10-15 times before reaching the feed mill.
Handling of raw materials can increase the frequency of broken or damaged particles or grains, thus increasing the risk of microbial and mould contamination. Controlling the quality of feed ingredients is an important component of feed operations and an important first step in preventing contamination among farm animals.
Feed ingredients can be contaminated by a large number of potentially pathogenic micro-organisms. The pathogen most frequently associated with animal feed and the subsequent contamination of eggs and poultry meat is Salmonella.
While processed animal proteins and protein by-products have long been associated with an increased risk of microbiological hazards, oilseed products and vegetable protein sources can also be contaminated at a similar rate if the bacteria are present either during or after processing. Apart from Salmonella, other pathogens to be considered within the feed mill¡¯s HACCP plan would include E. coli, Clostridia, Staphylococcus, Streptococcus and moulds.
Although the poultry industry has been the focus of attention for Salmonella control, the pig industry should be equally concerned as Salmonella infection results in increased mortality, lower daily gain, poorer feed conversion and higher medication costs.
Because microbial screening of raw materials prior to delivery is impractical and expensive, Salmonella and other harmful pathogens will often be present within a feed mill. Ingredients should always be inspected upon arrival at the feed mill and rejected if they are visibly contaminated with bird or rodent faeces. Even if a load tests negative for Salmonella, the random distribution of pathogens in a feed material could mean the consignment is contaminated. It is sensible therefore to assume that most raw materials may be potentially contaminated.
Once at the feed mill, handling and storage of raw materials is very important to prevent pathogen accumulation. Rodents and birds must be kept out of feed mill facilities, including the ingredients and finished product storage warehouses.
Silos must be cleaned regularly using dry cleaning techniques and fumigation. Water should not be used inside the silo as moisture is a precursor for pathogen and mould growth. Dust control is equally important, particularly if intake pits are located close to the finished product loading area. Dust extraction units should be installed to minimise the problem of dust contamination. Intake pits must be always kept clean and they should be covered when not in use to deter ingress from rodents and birds.
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