Effective control of Salmonella in feed
The control of Salmonella in the animal industry is one of the major challenges. Salmonella is found everywhere and can survive, even at low moisture levels, for a long time. Due to the complexity to control Salmonella, several measurements need to be taken to reduce contamination, growth and survival of Salmonella in feed.
A ubiquitous threat
Salmonella is found everywhere and can survive, even at low moisture levels, for a long time. Due to the complexity to control Salmonella, several measurements need to be taken to reduce contamination, growth and survival of Salmonella in feed.
Salmonella are one of the leading pathogens associated with reduced animal performance and food-borne illness in consumers. Contaminated feeds and critical feed materials such as oil seed meals and animal derived protein meals are among the major pathways through which Salmonella enter the animal food production. The link between animal feeds and both human and animal salmonellosis was already established many years ago. However, as Salmonella are ubiquitous and persistent in a wide range of materials, they are difficult to tackle with only a single control measure. Thermal processing is one of the important measures to kill bacteria in feed but may not completely eliminate Salmonella (re)contamination. In many cases, a combination of heat treatment and chemical treatment is used to kill bacteria.
Control of Salmonella in feed
Salmonella is very difficult to control, and every possible tool needs to be used in the prevention programme. Therefore, in general three different strategies are combined to eliminate Salmonella presence in animal feeds. At first, it is important to minimise contamination of ingredients and/or feeds. Secondly, measures should be taken to prevent bacteria from propagating in the feed. A third approach should focus on trying to kill off pathogens as much as possible.
Feed ingredients, arriving at the feed mill, are regarded as the predominant source for Salmonella contamination. During each of the subsequent processing steps, additional contamination can occur. Some ingredients have more than 10 processing steps before it arrives at the feed mill. Therefore, a selection of suppliers which are able to provide a specification that their products are Salmonella negative is essential. At arrival, care should be taken that the ingredients don"t contaminate the rest of the feed mill. Dust has hereby been considered as a key risk factor in the mill. In addition, maximal eradication of rodents, birds and insects inside the feed mill, is a must, as they all can be carriers of Salmonella. Likewise, people who work in the plant are an important factor in spreading Salmonella. Special clothing and shoes can help to reduce contamination risk. Needless to emphasise that, within the whole hygiene protocol of the feed mill, working with clean trucks that transport the final feed to the customers is of critical importance as well. Sanitation protocols should be implemented both for trucks that deliver the final feed as well as those that deliver the feed ingredients.
The most important criterium for growth of bacteria is moisture. In general, the environment of the feed mill contains not enough moisture for allowing bacteria to grow. However, there are some sources of moisture that are very difficult to avoid such as condensation or high environmental humidity. In addition, during manufacturing process, moisture is sometimes used as a "hygiene" measure, e.g. in the conditioner to increase temperature. This moisture can enable Salmonella to survive and grow, particularly when Salmonella is present in niches in the spots somewhere in the production system. Finding those spots is an important task of the mill personnel. A good sampling method and risk assessment can help to identify those growth niches.
Killing of Salmonella
In principle there are two measures to kill bacteria in the feed mill process; heat treatment, particularly via pelleting, and/or chemical treatment. Chemical treatments are generally done via the addition of acids to the diet. Formic and propionic acids are the most common used acids and numerous tests have proven their ability to kill Salmonella in animal diets. The efficacy of acids varies a lot and depends on numerous factors such as diet composition, moisture level in the diet, physical form of the diet, inclusion level of the acid blend, the composition of the acid blend, the chemical form of the acid product (e.g. pure acids or salts of acids). Organic acids, like formic and propionic acids, have multilevel effects:
In the feed
Organic acids have the ability to disturb the intracellular pH regulation and metabolic process of different bacteria. Besides their bacteriostatic properties, they also have direct toxic effects against various potential intestinal foodborne pathogens.
In the plant
Organic acids have residual, long-term protective effects in feed, which reduce recontamination and cross-contamination from milling and feeding equipment.
In the animal
The antimicrobial action of organic acids is not restricted to the feed matrix but also related to the proximal parts of the digestive tract. However, organic acids also trigger additional effects beyond antimicrobial activity: balanced commensal intestinal flora, improved activity of digestive enzyme, increased pancreatic secretion and empowered gastrointestinal mucosa.
It has been demonstrated long time ago that there is a clear link between animal feed and the presence of Salmonella in animals and even in humans. Because Salmonella can be found anywhere and is able to survive easily for a long time, a thorough control strategy needs to be implemented. At the feed mill, three different strategies should be considered: preventing multiplication, avoid growth and killing bacteria. Heat and chemical treatment of feed are efficient in killing bacteria like Salmonella, whereas the chemical treatment has not only benefits for the feed, but also for the plant and animal. Moreover, acidification is an essential part of a multifunctional approach for optimal Salmonella control in feed production.
Nutriad offers a multi-level approach in the prevention of Salmonella:
• Decontamination of Salmonella critical raw materials and feedstuffs
• Residual protection against re- and cross-contamination
• Broad spectrum activity against other foodborne pathogens and mould and yeast growth
• Improves drinking water hygiene
• Supports feed intake and digestion
• Reduces horizontal transmission of feed-borne pathogens
• Gut empowerment
• Improved animal performance
• Reduction of Salmonella colonisation
by Karen De Ridder, Business Development Manager Preservation & Functional Ingredients, Nutriad, Belgium