How to prevent and control Salmonella in feed and feed ingredients?
How to prevent contamination in feed manufacturing environment:
Several researchers have indicated that contaminated feed ingredients are the main source of Salmonella in the feed manufacturing environment. It is advised to assume that all raw feed ingredients are contaminated. Contamination can occur during processing and handling, with some ingredients being handled multiple times before reaching the end user. Therefore, it is important to communicate Salmonella-negative specifications to ingredient suppliers and purchase ingredients only from suppliers with a proven record of Salmonella control.
Upon receiving ingredient loads at the manufacturing facility, it is crucial for mill personnel to inspect each load for signs of contamination and reject loads with indications of contamination.
Dust control is essential, as it has been recognized as a major source of Salmonella contamination in feed mills. Dust can be generated at various points in the feed mill, including the raw ingredient receiving area, hammer mills, roller mills, mixing systems, and packaging areas. Effective dust control measures must be implemented throughout the facility to ensure Salmonella control.
Design dirty/ clean facilities: In a soybean processing facility, the ultimate contamination source was the incoming soybeans. While contamination rates in the receiving area were relatively low, operators were identified as the main source of Salmonella cross-contamination in the plant, particularly through work shoes. To prevent cross-contamination, it is important to designate areas within manufacturing facilities as “dirty” or “raw” and restrict the movement of personnel, equipment, and airflow from these areas to “clean” or “processed” areas.
Reducing oil or fat accumulation: Soybean oil appeared to protect Salmonella from environmental conditions, making it difficult to eliminate in areas with fat accumulation. Therefore, reducing oil or fat accumulation in the feed mill environment is important to decrease the survival and spread of Salmonella.
Control rodents: Rodents play a major role in spreading Salmonella contamination in the surrounding environment. High Salmonella contamination rates, up to 47%, have been reported in sampled rodents (F.T. Jones, 2011). To address this issue, rodent control measures should be incorporated into Salmonella control programs in feed manufacturing facilities.
Control wild birds: Wild birds are another potential source of Salmonella contamination, as they can carry the bacteria from various sources such as garden feeders, sewage, landfills, carrion, drinking water, animal feces, or nearby feed. In certain types of wild birds, Salmonella may even become a permanent part of their intestinal flora. Controlling wild birds is therefore crucial in feed mill Salmonella control programs
Use sanitary transportation: Transport vehicles, such as trucks or rail cars, have also been identified as potential sources of contamination. Ideally, vehicles used for delivering raw ingredients should be dedicated solely to such deliveries and thoroughly cleaned after each delivery. However, this may not always be feasible from an economic or logistical standpoint. At the very least, haulers should be required to disclose the contents of the last three loads delivered and provide information on the cleaning procedures used on their vehicles.
How to reduce the multiplication of Salmonella in animal feed?
Identify growth niches: In manufacturing environments following good manufacturing practices and including a “kill” step, most Salmonella contamination is attributed to microbial growth niches within the manufacturing system. Each feed manufacturing facility is unique, so it is the responsibility of personnel in each facility to identify these growth niches.
Construct a flow diagram: By constructing a flow diagram of processing steps and conducting hazard analyses by testing products before and after each step it is possible examining potential contamination at each step of the feed processing system to identify microbial growth niches.
The raw ingredient receiving operations area in feed manufacturing facilities is widely recognized as the primary location of heavy Salmonella contamination. This area is the source of most Salmonella-positive samples and the highest dust emissions in feed plants. Therefore, it is crucial to focus Salmonella control efforts on this specific part of the plant.
Controlling moisture: Controlling moisture is crucial in controlling Salmonella contamination in feeds and feed manufacturing. While some moisture sources like roof leaks are obvious, feeds can also gain moisture through condensation or absorption from humid air. Neglected microbial control measures can lead to the endemic presence of Salmonella, making eradication challenging due to the formation of biofilms on equipment surfaces.
Appropriate design and maintenance of systems: However, poorly designed or maintained systems can generate heat in ground materials, leading to moisture migration and concentration, which can facilitate microbial growth, including Salmonella.
Pelleting systems (thermal processing) have been shown to reduce Salmonella isolation rates by 50 to 93%. These systems rely on steam addition for pathogen destruction, but the steam also adds moisture to the pelleted feeds. While well-functioning pelleting systems remove the added moisture through pellet coolers, contamination in coolers may be higher due to increased moisture from condensation on interior surfaces, which creates favorable conditions for Salmonella growth.
How to kill Salmonella in animal feed?
There are various methods to kill Salmonella in feeds, including pelleting (thermal processing), chemical addition, or a combination of both. Several factors influence the effectiveness of these strategies. Therefore, regular monitoring of control methods is essential to assess their effectiveness.
The pelleting process consists of three major steps: conditioning, pelleting, and cooling.
Conditioning is considered the most crucial part, where steam is added to the feed, increasing its heat and moisture. This activation of chemical inhibitors and the reduction of pathogens like Salmonella occur during this stage. Factors such as temperature, time, and moisture play a significant role in microbial lethality during conditioning. Target temperatures of 175 to 185°F (80 to 85°C) are recommended, and conditioning times can vary depending on the equipment used. Expanders and extrusion-based systems can also be employed to enhance microbial lethality.
The pelleting process, without augmentation, can effectively reduce Salmonella isolations by approximately 80 to 85%. However, its effectiveness may be limited by factors such as feed composition, recontamination, or both.
Chemicals, mainly blends of organic acids (e.g., formic and propionic acids) and formaldehyde, have been used to control Salmonella in feeds. Proper application of these chemicals can protect against recontamination, but controlling Salmonella cells already present in the feed may be more challenging. Higher temperatures during feed processing can increase the effectiveness of organic acids. However, high inclusion rates and extended periods may be necessary for organic acids to destroy existing bacteria. Formaldehyde has demonstrated superior decontamination compared to acid products but has the disadvantage of being volatile and potentially evaporating in open systems.
Proper protection for workers is necessary, and some commercial formaldehyde-based products may contain additional antimicrobial compounds to mitigate evaporation effects.
It is important to note that organic acids and formaldehyde must be used to ensure no residues are left in the animal products (meat, milk, eggs) and that they do not adversely affect animal health or feed production processes.
How to control and prevent Salmonella?
Regarding your facilities, you need specific prevention or control measures. The most important measures are appropriate hygienic practices, thorough cooking and refrigeration.
Below you can find different prevention and control measures depending on the facilities you are.
Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Division of Foodborne, Waterborne, and Environmental Diseases (DFWED)
Ontario Ministry of Health, Ministry of Long-Term Care, Salmonellosis
Popa GL, Papa MI. Salmonella spp. infection – a continuous threat worldwide. Germs. 2021 Mar 15;11(1):88-96. doi: 10.18683/germs.2021.1244. PMID: 33898345; PMCID: PMC8057844.
Giannella RA. Salmonella. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 21. Available from: https://www.ncbi.nlm.nih.gov/books/NBK8435/
F.T. Jones, 2011, A review of practical Salmonella control measures in animal feed, Journal of Applied Poultry Research, Volume 20, Issue 1, Pages 102-113, ISSN 1056-6171, https://doi.org/10.3382/japr.2010-00281.