Control of Salmonella in feed

Published on : 30 Aug 2022

Certain ingredients are at a greater risk of being contaminated by Salmonella. Pest control, and adequate drying are important for cereal producers – chemical treatment of grain may be required. However, the removal of formalin as treatment, for health and safety reasons, has limited options for feed manufacturers. Processing of soya and oilseed rape also needs to be under strict control – with feed mills operating a programme of regular testing of raw materials and finished feed for Salmonella. Pelleting reduces some of the risk, but non heat-treated mash feed has a greater risk. Organic acids can be added to raw materials and the feed, in order to prevent bacterial contamination of feed. Other additives are added to support gut health and deal with bacterial challenges on farm.

Feed Hygiene
Salmonella present in animal feed is a significant source of infection in poultry. Due to the transmission of Salmonella enterica from feed to birds, then to human food, Salmonella in animal feedstuffs is considered a public health hazard. Salmonella infections are among the most common food-borne infections affecting humans in the EU. Animal feed ingredients, particularly animal and plant-derived protein meals, are frequently contaminated with Salmonella either from the source, from the processing plant or via recontamination in feed mills.

The methods for production of Salmonella-free feed involve preventing contamination of ingredients and/or feeds and preventing pathogen growth. Since microbial hazards may be introduced into various steps of feed production and delivery to the farm, technologies or products that provide long-lasting residual activity are essential. Technologies need to both be effective at reducing levels of Salmonella and provide protection from recontamination. Options include heat treatment and organic acid, as well as probiotics and other feed additives.

It’s not just about controlling Salmonella
Christophe Michaut, business development manager at Perstorp focusing on feed hygiene and antioxidants, has been working with feed producers on feed hygiene strategies for many years. “Although Salmonella is often the bacteria focused on, millers need to be thinking about bacterial contamination as a whole. This may sound contradictory to EU legislation. However, we only sometimes see Salmonella but if we are controlling overall bacterial contamination every day then we will be controlling Salmonella at the same time. Conversely, if we focus on one specific bacteria, we may be missing other issues that are having a negative effect on bird health and performance.” Bacterial contamination leads to digestive disorders, which potentially reduces performance. As well as causing wet litter, affecting bird welfare and increasing the number of dirty eggs – causing considerable financial losses.

The first area to consider is raw materials that are coming into the mill. Christophe explained that whole grains such as wheat and barley are low risk as they are still encased in their natural protective layer. However, it is still important to do general quality control checks; cereals should have been dried sufficiently and should not have signs of damage, like cracked grains. In terms of storage there needs to be good ventilation to prevent grains becoming damp.

Risky raw materials
“High risk ingredients are those that have been crushed, ground or otherwise processed – so that their natural protection has been removed - things like soy, sunflower and rapeseed meals. The seeds have been crushed and heated to 80-100ºC to remove the oil. The cooling process that follows creates condensation and the air used may be dirty, allowing mould and bacteria like E. coli to grow. This cooked free protein, with easily digestible amino acids, is now available to bacteria, in an ideal still-warm environment.” Christophe highlighted that with these kinds of products, including DDGS, it is recontamination of the products after processing, rather than any problem with the original raw material. 

Feed millers should therefore be testing these risky raw materials more often, as part of the quality control process. It goes without saying that millers should be working with reputable suppliers, who also have their own quality standards in place to minimise risk. However, it is the whole of the feed mill, which is at risk if a contaminated raw material is bought in. The onus is then on the miller to test and take step necessary to reduce the risk.

“For these risky materials it is common practise to treat them as they are moved from the reception pit into the silo. Organic acids are added at one to two litres per tonne at this point when flow is relatively slow – around one tonne per minute. The organic acids work efficiently, eliminating bacteria within a few hours. It will also continue to work within the silo, reducing the likelihood of recontamination.”

Processing power
The added challenge for layer feed, over that for broilers, it that is generally fed as a mash – so the raw materials are just ground and mixed. In contrast with pelleted feed, where the heat involved in extrusion and pelleting, reduces bacterial load at the end of feed manufacturing. “It could be said that it is even more important for there to be optimum control process in place for layer feed. However, the risky raw materials pose the same threats not just to the feed but the manufacturing plant as a whole.” Christophe re-iterated that both heat and acid treatment will kill Salmonella first. Other enterobacteria will survive longer – so if you control overall bacterial load, by default you are controlling Salmonella. However, heat treatment has no residual activity after treatment, meaning that this method will not prevent recontamination of feed post-treatment. Temperatures obtained during heat treatment can negatively affect nutrients and enzymes. Whilst it isn’t commercially possible to heat treat mash feed, pelleted feed can be crumbled but this would significantly increase costs.

Feed treatments
Formaldehyde has been a staple of feed pathogen control around the world for decades. However, EU Member States voted to deny the authorisation of formaldehyde for use as a feed additive for control of Salmonella in feed. Christophe is philosophical about the formaldehyde issue. “It is a strong, cheap and very effective product, but the problem is that feed producers could get away with less control because it was so effective. However, the concerns over operator safety, as well as animal health and environmental concerns – outweighed the benefits to feed hygiene. In the post-formaldehyde era, feed millers and poultry producers need to completely re-think their feed hygiene strategy.” This potent treatment meant that mistakes could be made and got away with. Many people believe it’s not surprising that more bacterial challenges and issues with Salmonella are currently being seen.

The protection of breeders from Salmonella contamination plays a crucial role in preventing the vertical spread of the infection to their progeny and in keeping the supply chain safe. Although Salmonella may be introduced to a flock by multiple environmental sources, feed accounts for 80% of the Salmonella infections in breeders and their progeny. Therefore, producers of breeding birds may now have to use more antibiotics to treat Salmonella-infected flocks, which goes against current international efforts to fight antimicrobial resistance.

Organic acids
Organic acids, such as formic, propionic, acetic, fumaric, caprylic, lactic, etc., have been used as bactericides for feed and as acidifiers to improve intestinal health. The efficacy of organic acids in reducing bacteria in feed is dependent on usage rate, initial level of bacteria, feed composition, and time between treatment and feeding. Organic acids are sometimes used in combination with heat treatment to further reduce risk.

The supplementation of organic acids at the right high doses in animal feed can increase the bodyweight, improve feed conversion ratio and reduce colonization of pathogens in the intestine. More specifically they decrease the pH value and the buffering capacity of the feed. As Inhibiting growth of gram-negative bacteria in the gastrointestinal tract. Organic acid products are also available for dosing into the water. This improves the quality of the water by preventing microbial growth but also improves gut health once drunk.

Although organic acids have been used in animal feed for 30 or 40 years, it is the effects in the animal themselves, which have mostly been evaluated. “Particularly in light of the ban on formaldehyde, organic acids that are being used to treat feed, need to be evaluated in terms of their efficiency to reduce bacterial load in feed and prevent recontamination. In fact, digestive disorders are indicative of other gram-negative enterobacteria, such as E. coli not Salmonella.” There are a lot of options available, each with their pros and cons. The efficacy of the product should match the job it is intended for.

Formic acid (85%) is regularly used to treat feed and is not expensive. However, by looking for a specific feed hygiene enhancer, greater benefits can be seen. Clever technology can result in even lower levels of feed contamination as well as reducing the potential for recontamination. Distribution of products in feed can be improved, along with continuing acidification.

Supporting the gut microflora
In addition to organic acids, there are various feed and water additives that are been used to reduce Salmonella colonisation in the animal. Prebiotics and probiotics are often used to prevent dysbiosis in animals. In poultry production, managing gut health is key to optimising performance. If there is an imbalance in the gut microflora, inflammation will occur – negatively effecting gut integrity. Not only does it make birds more susceptible to infection, it may reduce nutrient absorption and lead to digestive upset.

The effect of better microbial diversity in young broiler chicks will help gut development, improving future performance. For this reason, the practise of seeding the gut of chicks has been used for many years. They are either sprayed onto them, dosed into the water, added to the feed or provided as a specific supplement. The options for probiotics products, for poultry and other livestock species, are numerous: Lactobacillus, Bacilli, Bifidobacteria, Enterococci and yeasts; single- or multi-species and combined with prebiotics or other immune supporting additives. By improving the balance of the gut microflora, the aim is to create an optimum environment to reduce the growth of pathogens, improve immunity and prevent inflammation; as well as enhancing digestion and nutrient absorption.

Clever feed hygiene
Perstorp has been working with feed producers on targeted sampling, as part of the control process. “Raw materials should be tested both before and after treatment with organic acids. We ask feed producers to send samples to us every two weeks, as part of an on-going monitoring service. Analysis of the results evaluate whether the treatment is effective, enabling millers to modify their control plans accordingly. This may mean changing the dosage rate or timing of application. They should be looking at a minimum of a 1 log reduction in enterobacteria, in order to indicate a significant effect. However, if you are making feed for breeding birds you would want to aim for a 3 log reduction. Again, if you aim for an excellent quality feed in these terms, you will be reducing Salmonella levels at the same time.” Some feed producers will also/or only, send in finished feed samples to monitor the ultimate level of contamination. The samples are also tested for the organic acids themselves, with a five kilogram per tonne addition they see recovery levels of ~ 10%. This way the effectiveness of the treatment is monitored and issues with application or re-contamination within the mill can be addressed. “Where an issue within the process is suspected, millers may take samples at several points along the line. Along with an audit of the facility, areas of recontamination can be identified and addressed. For example, a dead end where feed is accumulating, or an elevator which is not being cleaned properly.”

Obviously, the amount that the bacterial load can be reduced with, will be dependent on the level of contamination in the raw material on delivery. Millers will have agreements in place that product from approved suppliers, will meet certain specifications. However, although samples are taken at delivery, results will not be available for several days. So, the truck still needs to be unloaded and the products treated and re-tested – to avoid contamination of the mill. “After this process if there was a very high accidental contamination of a raw material – a decision can be taken to not use that batch. This situation is probably only 0.5% of cases – generally acidification reduces bacterial whole by one to two logs - a level safe for use.”

Home mixers
Feed hygiene can be more of a challenge for home mixers, with small equipment and less ability to invest in specific equipment. “Mobile mixers often use the same three to five tonne mixes, which are mixed for around three minutes. This includes a 30 second dry mix at the beginning and end. So, it means there is a two-minute window to add any liquid products. organic acids can be sprayed on at this point and similarly samples should be taken pre-and post-treatment to ascertain the efficacy of the application.” However, without the infra structure of a large feed manufacturer, it is important to focus on biosecurity on the farm in general and particularly during the mixing process.

Ideal strategy
Christophe explained that the ideal strategy for feed hygiene would be to treat all risky raw materials before they go into the silos. And then treat the complete feed again at mixing. “The first treatment is for internal safety of stopping contamination coming into the mill. Then the second step addresses any re-contamination, helping to produce a safe feed for the customer and the birds eating it.” Taking this kind of integrated approach is key in the fight against bacterial contamination and Salmonella control. 

Integrated approach
The microbial safety of animal feed is paramount to public health. As such there will always be an obligation for the industry to do all it can to reduce bacterial contamination of feed. And with pressure to reduce antibiotic usage and improve sustainability, feed hygiene solutions need to be effective and integrated with Salmonella control throughout the food chain. As well as giving the public confidence in the eggs they are buying. This, combined with financial pressures means that strategies, which also improves bird health and performance, offer benefits to egg producers.