Salmonella spp. is one of the major hazards for the microbial contamination of animal feed. On-farm Salmonella control is an important issue, directly linked to regulatory limits at slaughter and public health concern. Effective Salmonella control on the farm is based on the prevention of Salmonella entering and spreading in a farm.

Salmonella is a common component of the gut microflora of animals and thus, can be found in the faeces of affected animals. Faecal pollution is the main culprit for the contamination of feed and water with Salmonella. Pigs can also become infected and act as reservoirs of Salmonella. In order to ensure a pig's high level of 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 prohibiting Salmonella occurrence and contamination.

Points of Salmonella Control

The points of Salmonella control include: breeder houses, feed raw materials and compound feed, water, the farm environment, vermin control and prohibiting cross-contamination.

Breeder houses

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

Feed

Salmonella spp. is one of the major hazards for the microbial contamination of animal feed. 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 by consuming Salmonella contaminated feed, which can be further carried over to products of animal origin.

It is important to check all raw materials, especially cereals and protein sources, for Salmonella contamination. Salmonella colonies are naturally unevenly distributed in feed and therefore, the detection and quantification of Salmonella can be difficult. Sampling feed from different places is necessary to get the representative feed sample for microbial analysis. Therefore, preventing the spread of Salmonella is a recommended tool for Salmonella control.

The 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 protect feed from recontamination during transportation and storage, as can be seen in Figure 1.

Figure 1. Recontamination of feed without acidifier

A multiple strategy encompassing heat and antimicrobial treatments, for instance, with organic acids, is required for the reduction of bacterial burden and improvement of feed hygiene.

The addition of organic acids has been shown to contribute to environmental hygiene by preventing feed raw materials and compound feed from microbial and fungal deterioration. Moreover, it contributes to good farm management and interrupts the bacterial transmission in the animal-to-food chain. It is generally known that acids can reduce the number of Salmonella because of the reduction of the pH level and also because of their antimicrobial activity in the feed and gastrointestinal tract. The non-dissociated form of organic acids penetrates into the bacterial cell, prohibiting its replication. Biomin provides a family of products that combines synergistically acting organic acids and other components to strengthen the antimicrobial activity of acids.

The in-vitro trial was conducted to determine the efficacy of an acidifier consisting of formic and propionic acids that act on Sequential Release on Salmonella contamination in feed. Feed was artificially contaminated with a high level of Salmonella enteritidis. The metabolic activity of Salmonella is reduced in dry feed, which lowers their rate of replication. The feed was diluted with physiological saline solution and the cell count of Salmonella was determined right after contamination, after one hour and 2.5 hours of incubation under optimal conditions. Results can be seen in Figure 2. Salmonella replication was steadily growing under optimal conditions while the number of Salmonella was decreased in the group containing the acidifier.

Figure 2. Effect of acidification on Salmonella reduction in feed

Water

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 for animals should have the same high standards as that suitable for human consumption. The results of the two samples taken from the start and end points of the watering line, and the difference between them, gives a clear picture of whether improvements in water quality have to be made.

Water acidification can help prevent Salmonella. The supplementation of acids in drinking water reduces the pH level and bacterial counts. The reduction of pH value in water creates unfavorable conditions for potentially harmful bacteria proliferation. A very important feature of water acidification is the lowering of the pH level by adding acidifiers. 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 pH4 and this has a negative impact on the equipment as well as the water intake and growth performance 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 help to minimise the danger of infection.

Improving farm personnel hygiene and the control of visitors are important factors for reducing the risk of Salmonella. Hand washing 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 is offset by a reduced transfer of other performance impairing pathogens.

Vertebrate and invertebrate species

Since all vertebrates are susceptible to Salmonella infection, contact with other species may pose an infection risk to 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 vectors for Salmonella. It is therefore important to ensure proper vermin and pest control on the farm.

Cross-contamination

As animals have a lot of contact with each other the spread of infection can be very fast. Aiming for small group sizes with minimal mixing of animals contributes a lot to the prevention of Salmonella spread. It is also important to not let sick animals come back into the main production unit.

Salmonella control is key to preventing Salmonella outbreaks on the farm. The acidification of feed minimises Salmonella infection and contributes to enhancing the overall performance of animals. Effective Salmonella control on the farm is based on the prevention of Salmonella entering and spreading in a farm.

February 2013