Despite great efforts during production and between sectors, Salmonella remains a massive public health concern. Additionally, the economic impact of an on-farm outbreak cannot be underestimated. Nowadays, understanding about the transfer and proliferation of Salmonella has increased significantly, including the realisation that Salmonella control requires a holistic approach.
Veterinary considerations: prevalence, treatment and prevention
Salmonella infection is quite common in pigs in the European Union (EFSA Report, 2022). It usually courses asymptomatically, but infected pigs may shed the bacterium through their faeces, making them a major risk factor for carcass contamination at slaughter.
The clinical disease is characterised by three syndromes:
- a systemic septicaemia which may precede enteritis
- enteritis with some degree of local invasion
- colonisation of the intestine and intestinal content without further penetration
Less common are clinical presentations including abortion, arthritis and respiratory disease.
Antibiotic treatment of Salmonella infections must be based on susceptibility data of Salmonella spp. and knowledge of drug susceptibility patterns of Salmonella strains found in the area or in the corresponding country.
Affected animals can be treated individually by daily injection or via water and feed with a suitable antibacterial agent for enteric (Apravet®, apramycin) or systemic treatment (HydroTrim®, trimethoprim-sulphonamide; Amphen®), florfenicol). Preferred antibiotics to be used are those listed in group C and D of the EMA Categorisation List of Antibiotics.
Prevalence figures of porcine enteric infection outbreaks indicate that Salmonella spp. is often identified as part of mixed enteric infections. Consequently, diagnostic examination is very important to identify the individual pathogens possibly involved in enteric infections.
Every effort must be made to reduce the presence and the prevent the spreading of Salmonella spp. in pig herds. During the grower-finisher phase, Salmonella presence is directly related to carcass contamination at slaughterhouses. Ideally, pigs going to the slaughterhouse should be Salmonella-free. In practice, Salmonella is endemic on most farms and Salmonella preventive programmes to stop spreading from carriers should be established.
Preventive strategies and feed additives
Probiotics have been added to the herd managers' toolbox to help mitigate Salmonella during production.
A Clostridium butyricum strain-based probiotic, such as Top Gut®, has shown to be an efficient tool for farm gut health management plans, playing a key role in swine farm strategies for the mitigation of food safety related pathogens such as Salmonella.
The efficacy of Top Gut® can be attributed firstly to the C. butyricum strain being a spore former. In its spore form, the bacteria can pass through the more hostile environment of the initial segments of the gastrointestinal tract without losing viability. Once the spore reaches a location with the right conditions, it germinates into active vegetative cells. Secondly, C. butyricum is an obligate anaerobe, meaning that it will only germinate when and where oxygen concentrations are low enough (at the hindgut level). C. butyricum ferments the available substrate in the hindgut releasing significant amounts of butyric acid which the animal uses in its butyrate-dependent metabolic processes. Lastly and of key relevance, the proliferation of C. butyricum keeps the environmental conditions adverse to the overgrowth of pathogenic bacteria, such as Salmonella.
Several field trials validate the use of Top Gut® as part of farm strategies to mitigate Salmonella prevalence, showcasing the impact of using such a probiotic as a mitigation tool, or as part of a preventative program. The results of a field trial are summarised in Figure 1.
The trial was carried out on a pig farm dealing with clinical diarrhoea and a Salmonella level 2 rate (high seroprevalence in carcasses). The probiotic treatment (Top Gut®, 5 x 108 CFU/g product) was added during the full trial period with the dose rate being adjusted depending on body weight (BW): 1 kg/t of feed from 10 to 40 kg BW followed by 0.5 kg/t of feed from 40 kg BW until slaughter. Salmonella seroprevalence was measured by sampling at the start of the trial and at the end (approx. 40 samples were analysed per sampling moment).
The results clearly show that the farm saw a significant Salmonella seroprevalence drop with Top Gut®. In addition, the inclusion of C. butyricum significantly lowered the relative risk of a carcass being classified as Salmonella seropositive. Overall, the probiotic program allowed the reclassification of the tested farm to Salmonella level 1.
Conclusion
Salmonella infection is quite common in pigs and despite affected animals being able to be treated with a suitable antibacterial agent (Apravet®, HydroTrim®, Amphen®), its impact on food safety due to potential carcass contamination is high.
Salmonella control strategies need to be considered in farm health management plans. Such strategies should take into consideration multiple factors in the production system.
A Clostridium butyricum based probiotic, Top Gut®, demonstrated that it has an essential place as part of a farm gut health management plan, playing a key role in strategies for mitigation of food safety related pathogens, such as Salmonella, in pig farming.
References are available on request.
