The use of acidifiers in controlling Salmonella

Salmonella control is key to preventing the introduction of Salmonella on the farm. Correct farm management, biosecurity measures, targeting small groups of animals and preventing the return of sick animals to the main production unit all contribute to the prevention of Salmonella spread. Acidification of feed and water minimises Salmonella infection and promotes good gut health, thereby enhancing the performance of animals.

By Nataliya Roth, Product manager acidifiers, Biomin Holding, Austria

Effective Salmonella control on the farm is based on preventing Salmonella from entering and spreading in a farm. Salmonella is a cause of bacterial food-borne disease in humans, and can often be attributed to contaminated food products. It is estimated that around 2.6%, 10.6% and 17.0% of human salmonellosis cases are attributable to turkeys, broilers and laying hens, respectively.

Salmonella is a common component of the gut microflora of animals and can be found in the faeces of affected animals. Faecal pollution is the main culprit for the contamination of feed and water. Poultry can also become infected and act as reservoirs of Salmonella. In order to ensure a high level of poultry performance, farmers should pay close attention to farm management and Salmonella prevention. Regular testing and observing the critical points of the production chain are necessary for preventing Salmonella occurrences and contamination.

There must be adequate Salmonella monitoring and control at the hatchery and breeder farms. Control starts with getting healthy young chicks to the farm. On arrival, the chicks should be Salmonella free. Samples from transport equipment and faeces should be taken to determine the Salmonella status.

Feed contamination

Salmonella spp. is the one of the major hazards for the microbial contamination of animal feed. In addition, antimicrobial resistant bacteria, or antimicrobial resistance genes can be transmitted viafeed. Animal-derived protein and oil seed meal are the major sources of risk among feed materials, through which Salmonella may be introduced to industrial compound feed and feed mills.

International regulations require that food and feed are free from Salmonella. Appropriate process control and decontamination steps are needed during feed processing to reduce the contamination of feedstuffs and avoid the dissemination of contaminated feed to herds. It has been demonstrated in experimental settings that animals can become infected as a result of consuming Salmonella contaminated feed. Some animals may show clinical disease symptoms or carry Salmonella without showing any symptoms. It is possible for Salmonella to be transmitted from the animals to food products derived from these animals.

It is therefore important to check all raw materials, especially cereals and protein sources, for Salmonella contamination. In general, counts of Salmonella in feed are low, but it is also important to know that Salmonella colonies are naturally unevenly distributed in feed thus, the detection and quantification of Salmonella can be difficult. Consequently, the prevention of the spread of Salmonella is a recommended tool for Salmonella control.

Multiple strategy

Heat treatment of feed is a common means of feed sanitation. However, it should be conducted appropriately in order to reduce bacteria counts, taking into account in particular, temperature, duration and initial bacterial counts. Moreover, heat treatment does not always protect feed against recontamination during transportation and storage.

A multiple strategy encompassing heat and antimicrobial treatments with organic acids is required for the reduction of bacterial burden and improvement of feed hygiene. Acid treatments have a residual protective effect on feed, which reduces both the recontamination of feed as well as the contamination of milling and feeding equipment and the general environment. The efficacy of organic acids against Salmonella depends on the level of bacterial contamination.

Dietary acidification that reduces the amount of Salmonella in feed contributes to good farm management and interrupts the bacterial transmission in the animal-to-food chain. An in-vitro trial was conducted to determine the efficacy of an acidifier based on formic and propionic acids in feed. Feed was artificially contaminated with a high amount of Salmonella enteritidis. In dry feed, the metabolic activity of Salmonella is reduced, which lowers their replication. The feed was diluted with a saline solution and the cell count of Salmonella was determined right after the contamination, after one hour and 2.5 hours of incubation under optimal conditions. Results can be seen in Figure 1. While Salmonella replication was growing steadily under optimal conditions, the number of Salmonella was reduced in the group with the acidifier.

Water acidification

Salmonella can persist and grow in water given the right conditions. The diversity and concentration of Salmonella increases as temperatures rise. For better Salmonella control, the microbiological test of water is needed, especially if the source of water is a well or river.

Water acidification can help prevent Salmonella. The supplementation of acids in drinking water reduces the pH level and bacterial counts. A very important feature of water acidification is the pH level and corrosive properties of the acidifier. Very often, farmers apply acids without knowing the pH level of water. If the acidification is too strong, the pH level of the water goes below 4 and this has a negative impact on the equipment and water intake of animals.

Farm hygiene and biosecurity

Contamination of the resident environment of animal housing can be a source of Salmonella infection. Keeping buildings clean and disinfecting farm equipment helps to minimise the danger of infection.

Improving farm personnel hygiene and the control of visitors are important factors for reducing the risk of Salmonella. Washing hands and disinfection as well as the cleaning of overalls and disinfection of boots before entering the stable are associated with decreased Salmonella prevalence. The relatively small cost incurred may be offset by decreased transfer of other performance impairing pathogens.

Since all vertebrates are susceptible to the Salmonella infection, contact with other species may pose an infection risk to other animals. Pests (rodents, wild birds, and other wildlife species) have often been implicated as potential sources of Salmonella. It has been recognised that flies and beetles also serve as a potential reservoir and carriers for Salmonella. It is therefore important to ensure proper vermin and pest control on a farm.

Natural feed additives

It is known that dietary supplementation with natural growth promoters (NGP) can assist in Salmonella prevention. In a trial 84 day-old broiler chicks (Ross) from the same origin were randomly divided into three treatment groups. The control group received no feed additives, whereas two trial groups received dietary supplementation with two different natural growth promoters.

Trial group I received a diet supplementation with an NGP consisting of a blend of formic and propionic acids at inclusion levels of 3.0 kg/t feed. Trial group II received a diet supplemented with an NGP consisting of a blend of organic acids, a phytochemical and a permeabilising substance at an inclusion level of 1 kg/t feed. A permeabilising substance was identified to weaken the outer membrane of Gram-negative bacteria and facilitate the entry of organic acids and phytochemicals in the cell disturbing its vital functions. At three days of age all chicks were orally inoculated, the challenged dose was 104 cfu/bird of Salmonella enteritidis.

At 7 and 14 days post infection (dpi), the caecal content from 12 birds was taken and analysed quantitatively and qualitatively for Salmonella. At 11dpi, faecal samples were taken and analysed qualitatively for Salmonella. The results of this study showed that in the groups supplemented with the natural growth promoters, Salmonella was neither detected in the quantitative and qualitative culture in caecal samples at 14dpi nor in the qualitative culture in faecal samples at 11dpi.The present trial results are in accordance with scientific literature which has shown that organic acid blends are effective in preventing the caecal colonisation of newly-hatched chicks by Salmonella enterica serovars Typhimurium, Enteritidis, Agona and Infantis (Iba & Berchieri Jr., 1995). This is consistent with previous findings by Hinton & Linton (1988), who reported that while a blend of organic acids did not completely eliminate Salmonella from treated feed, there was no caecal colonisation by Salmonella when this feed was given to the birds.