How to Control Salmonella During Poultry Feed Production

By Steve Bolden, Managing Director of World Technical Support

Fully controlling Salmonella during poultry feed production requires total commitment as, despite careful sourcing, some raw materials can be expected to enter the mill contaminated. When considering using feed technology to reduce Salmonella in a poultry production system, all of those involved need to ask themselves, “Are we really serious about this, or are we comfortable with just wishful thinking?”

In fact, many of those involved in making poultry feed will hesitate to add cost to the process to sanitize feed. Some examples of added cost are: elimination of ingredients that tend to be Salmonella positive, heat treatment of feeds that historically have been fed in mash form, and the extra labor and materials costs associated with sampling and monitoring. We must ask, “Do we really want to know if we have positive samples?”

control starts with good housekeeping

All areas of the feed mill need to be kept clean and tidy, and every mill employee should be obsessive about it.  For example, dust harbors Salmonella and provides a growth medium for microorganisms in general. So, all surfaces need to be swept or vacuumed and kept free of dust. Likewise, leaky conveyors and bins need to be repaired, otherwise dust reduction becomes difficult.
Also, the interior rooms in the mill should not become gathering places for debris, used parts and junk. Tidy, neat, clean and organized are the key descriptors of a mill where bacterial control is a priority. There should be no wild birds in any section of the feed mill.
If flat (open) storage exists, it must remain closed and protected from animals of any kind. This is difficult, and all open storage should be converted eventually to enclosed (bin) structures. Naturally, rodent control, preferably elimination, has to be another top priority in order to be serious about Salmonella control.

Prepare for positive raw materials

Monitoring of incoming ingredients, and the selection – or elimination, based on test results -- is important. However, we must recognize that raw materials coming into the mill will occasionally be positive for Salmonella
It is well documented that animal-derived products will present the greatest challenge, but it is not uncommon to see contaminated samples of corn, corn by-products, soybean meal, wheat by-products and even liquid fat. If your monitoring program does not show positive raw material results at some regular frequency, you are probably not doing adequate testing, or not using sensitive enough technology.
If you fully desire to identify your weak links in the raw material chain, make sure you test to the point of having confidence in the results. Unless a private arrangement is made between a supplier and a feed manufacturer, there are no trading rules on Salmonella in plant (vegetable) ingredients. So, supplier preference will need to spring forth from your own monitoring. But, despite all good efforts in raw material tracking and selection, there will be ingredients that go into the mixer that contain Salmonella.

Heating is vital

The most effective Salmonella control step in the mill comes from heating. The literature is full of temperature conditioning recommendations, ranging from 74C to 85C. Unfortunately, however, with the variation in conditioning time and moisture, there is no absolute number. Some tend to over-manage the heat application process and view it as “more is better.” In Cobb’s case, we extend our 90C conditioning times with the assistance of a hygieniser. Other feed manufacturers will use heat-generating machines such as annular gap expanders or extruders to infiltrate the feed with heat beyond the conditioner.

Clean cooler air

The heat step will be less effective if, when entering the cooler, the feed is met with dirty, contaminated air. This is why the cooler should have its own closed air supply, derived from a section of the mill least likely to create re-contamination with airborne bacteria.
The idea is to use filtered air that originates from the top of the mill or from somewhere that is dust free. Regardless of the air-cleaning method, the cooler cannot simply be an open vessel pulling air from a dirty area.

Clean and dirty areas of the mill
When considering Salmonella, the “dirty” areas of the mill are the reception area for raw materials, the warehouse, grinding, scaling and mixing, and all connected elevators and chutes from these spaces. The pellet mill and/or other heat-steps serve as the transition from clean to dirty – when feed is sanitized.
Therefore, the clean areas become the pellet mill exit chutes, the cooler, crumbler, finished feed legs, finished feed storage, load-out and associated elevators. Human traffic should be very limited when going from a dirty to a clean area in the mill, and it is a major advantage if these areas have walls or barriers separating them.
There are also some nice, elaborate air-handling systems that can pressurize the clean sections of the mill to help prevent cross-contamination from the dirty side. The bulk load-out bays can even be pressurized, in combination with doors that automatically close on truck entry and during the feed loading process. Control of airflow is a vital key to keeping sanitized feed from being re-contaminated with Salmonella.
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