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Salmonella in pigs

Salmonella in pigs

Salmonellosis diagnosis and Salmonella control on pig farms

Salmonella is an enteric pathogen that can infect almost all animals and humans. It is one of the major food safety hazards for humans. After a great sanitation effort in poultry sector to control the Gram-negative pathogen, Salmonella in pigs has now become a major concern.

Salmonella in pigs

Pigs can become infected and act as reservoirs of Salmonella. Salmonellosis in swine is caused by Gram-negative bacteria from the genus Salmonella. In order to ensure a high level of pig performance, farmers should pay close attention to farm management focusing on: Salmonella prevention, applying external biosecurity to avoid the bug entering the farm and internal biosecurity to void spreading the bug when already present in the farm.

Occurrence of Salmonella in pigs

Salmonella is capable of surviving at least 6 years or more in the environment (Funk et al., 2008). Therefore biosecurity related practice is highly relevant for reducing the risk of Salmonella in swine farming.There is an association between season and/or environmental temperature and Salmonella prevalence in finishing swine (Christensen and Rudemo 1998, Funk et al., 2001). According to Rajic et al. (2007) pigs fed pelleted rations were at increased Salmonella risk compared to those fed mash feed.

    The most frequently isolated Salmonella serotypes in pigs (Lowell and Barrow, 1999; Astorga et al., 2007) are:

    • S. Typhimurium
    • S. Choleraesuis
    • S. Derby
    • S. Brandenburg
    • S. Bovismorbificans
    • S. Newport
    • S. Bredeney
    • S. Anatum
    • S. Hadar
    • S. Goldcoast

    Weaned piglets

    Salmonella-induced diseases can occur in each stage of pig production, but piglets are most sensitive to it. The compound feed of juvenile animals like weaning piglets is high in protein and mineral content (high B-value).

    Diets with a high B-value increases stomach pH, almost jeopardizing the barrier function and decreases digestibility which provides a suitable environment for pathogenic bacteria. Low levels of amylase and trypsin activity have been observed in the immature digestive system of piglets.

    Another stress factor which should be taken into consideration in the case of weaned piglets is the diminished passive immunity and less developed active immunity. Environmental stresses caused by grouping, a diet change from sow milk to solid feed, and moderate development of the gastrointestinal tract (GIT) can facilitate the occurrence of Salmonella disease.

    Gestating and lactating sows

    Salmonella spp. can sometimes cause clinical diseases in sows like fever, depression, septicemia, pneumonia, meningitis, arthritis and diarrhea. According to Magistrali et al. (2011) young sows are more likely to shed Salmonella than older animals.

    The weaning period is the highest risk period for the excretion of Salmonella. Several factors could explain the increased Salmonella excretion at post weaning, such as stresses linked to the weaning and the significant reductions in feed and water immediately post-weaning.

    Fattening pigs

    Schultz et al. (2007) has demonstrated that 10- to 12-week-old pigs under cold-stress and market-age pigs that are heat-stressed (18-22 weeks old) are at a higher risk of Salmonella infection. By reducing the Gram-negative bacteria in the feed and GIT, FCR and average daily weight gain (AWDG) are improved.

    Control

    On-farm Salmonella control is an important issue which is directly linked to regulatory limits at slaughter and food safety. Effective Salmonella control on the farm is based on the prevention of Salmonella entering and spreading on a farm through robust biosecurity.

    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 on pig farms include:

    • Breeder houses
    • Feed raw materials and compound feed
    • Water
    • Pests
    • Farm environment

    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 feces 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.

    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, Figure 1 shows.

    Pests

    Since all vertebrates are susceptible to Salmonella infection, contact with other species may pose an infection risk to animals. Pests (pets, rodents, wild birds, and other wildlife species) have often been implicated as potential sources of Salmonella. It has been recognized 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.

    Figure 1: Recontamination of feed without acidifier | Source: Israelsen et al., 1996
    Figure 1: Recontamination of feed without acidifier
    Source: Israelsen et al., 1996

    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, a microbiological test of water is needed, especially if the source of water is a well or river. Drinking water for animals should have the same high standards that are suitable for human consumption. The results of the two sampling from the start and end points of watering line, and the difference between them, gives a clear picture if improvements in water quality that have to be made, if any.

    Feces

    Salmonella is a common component of the gut microflora of animals and thus, can be found in the feces of affected animals. Fecal pollution is the main culprit for the contamination of feed and water with Salmonella.

    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 minimize the danger of infection.

    Improving farm personnel hygiene and the control of visitors are important factors for reducing 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 may offset a decreased transfer of other performance impairing pathogens.

    Main biosecurity practices that can also reduce/control Salmonella prevalence include:

    • Changing of clothing and boots prior to entering or leaving the pig area
    • Cleaning and disinfection protocols (facility, feeders and drinker equipment)
    • Pig flow practices (all-in/all-out pig flow)
    • Welfare standards such as density and ventilation

    See 12 biosecurity tips to achieve peak efficiency and use antibiotics responsibly on your pig farm.

    Solutions

    The use of acidifiers or organic acids in the feed or drinking water can reduce the risk of Salmonella in swine farms. Research has shown the direct relationship between acidity level and Salmonella prevalence in pigs (Alborali et. al., 2012).

    Acidifiers exert their mode of action not only in compound feed but in the gastrointestinal tract (GIT) as well. Thus, the effects of organic acids may be targeted at three different areas: the feed, GIT and intermediary metabolism leading to improved feed conversion rates (FCR), digestibility of nutrients and reduced diarrhea (scours), morbidity and mortality rates (Figure 2).

    Figure 2. Mechanisms of organic acids
    Figure 2. Mechanisms of organic acids in feed, water, gastrointestinal tract and intermediary metabolism.

    Acidifiers in feed

    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.

    Because heat-treated feed can be re-contaminated by Salmonella, application of an organic-acid based product is recommended. An in-vitro trial was conducted to determine the efficacy of Biotronic® 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 the contamination, after one hour and 2.5 hours of incubation under optimal conditions. Results can be seen in Figure 3. Salmonella replication was steadily growing under optimal conditions while the number of Salmonella was decreased in the group containing 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.

    Salmonella in pigs' feed reduced with acidifier
    Figure 3. Effect of acidification on Salmonella reduction in feed

    Acidifiers in water

    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.

    Tip: It’s important to know knowing the pH level of water when determining the right dosage of acidifiers to pigs’ drinking water.

    BIOMIN solutions for Salmonella control

    Feed raw materials contaminated with Salmonella can be treated with higher doses of Biotronic® SE forte (8-10 kg/t) and Biotronic® SE forte liquid (5-10 l/1000 l).

    It is not recommended to include both acidifier and vaccine in the water simultaneously. Furthermore, avoid the use of certain β-lactam antibiotics in acidified water. The inclusion level of Biotronic® SE forte liquid depends on the initial pH of the water.

    Table 1. Recommended product application levels to control Salmonella in solid and liquid feeds, water, and the GIT
    Recommended product application levels to control Salmonella in solid and liquid feeds, water, and the GIT 
    ProblemSowsWeaner pigsFattener pigs
    Feed hygiene

    Biotronic® SE forte

    Biotronic® SE forte liquid 

    1-3 kg/t

    1-3 l/t

    Biotronic® SE forte

    Biotronic® SE forte liquid

    3-5 kg/t

    1-3 l/t

    Biotronic® SE forte

    Biotronic® SE forte liquid

    1-3 kg/t

    1-3 l/t

    Liquid feed hygiene

    Biotronic® SE forte liquid

    1-2 l/1000 l feeding

    Biotronic® SE forte liquid

    1-2 l/1000 l feeding

    Biotronic® SE forte liquid

    1-2 l/1000 l feeding

    GIT health

    Biotronic® Top3

    1-2 kg/t

    Biotronic® Top3

    1-2 kg/t

    Biotronic® Top3

    1-2 kg/t

    Combination to cover feed hygiene and GIT health

    Biotronic® SE forte

    Biotronic® Top3

    1 kg/t

    1kg/t

    Biotronic® SE forte

    Biotronic® Top3

    1 kg/t

    1 - 1.5 kg/t

    Biotronic® SE forte

    Biotronic® Top3

    1 kg/t

    1 kg/t

     

    Combination to cover water hygiene and GIT health

    Biotronic® SE forte liquid

    Biotronic® Top3

    1l/1000 l water

    1 kg/t

    Biotronic® SE forte liquid

    Biotronic® Top3

    1 l/1000 l water

    1 - 1.5 kg/t

    Biotronic® SE forte liquid

    Biotronic® Top3

    1 l/1000 l water

    1 kg/t

     

    Solutions

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