In the swine industry, Salmonella may be present during the entire production life cycle in pigs and disseminated in faeces for several weeks or months without signs of clinical disease. When Salmonella is present in the gastro intestinal tract (GIT), it might contaminate carcasses during the slaughter process, and become a source of food poisoning and bacterial gastro-enteritis in humans.

Ways of transmission for Salmonella

However, Salmonella infection may be transmitted during contact with animals, through contaminated water, or via the environment and may pass through the entire food chain from animal feed, primary production and all the way to households or food-service establishments and institutions.

In pigs and livestock in general, Salmonella will often not instigate disease, unless there are predisposing conditions such as the presence of pathogens or stress factors. Some associated serotypes including Salmonella Typhimurium phage type (PT) 12, and Salmonella Derby are more likely to infect finishing pigs and are considered major causes of food poisoning in humans.

Salmonella 2nd-most reported zoonosis

According to the European Food Safety Authority (EFSA) in 2015, salmonellosis represented the second most reported zoonosis as a major cause of human bacterial gastro-enteritis, after campylobacteriosis.

Non-typhoidal Salmonella species are estimated to cause 93.8 million cases of gastro- enteritis and 155,000 deaths worldwide each year, about 85% of which are estimated to be foodborne, establishing Salmonella as having a significant public health and economic impact on society. Pork products are among the top food-borne sources of Salmonella globally, which also has a negative impact on the agri-food and trade sectors, due to costly recalls of contaminated products.

Harmful strains to antimicrobial drugs

A particularly worrisome trend concerns the worldwide rapid emergence of resistant harmful strains to antimicrobial drugs. The use of closely related antimicrobials in human and the swine industry has led to an increase and persistence in multidrug- resistant particularly strains of Salmonella, Campylobacter and E. coli.

It has been documented that Salmonella strains can acquire antibiotic resistance in animals, before transmission to humans through the food chain. In pigs, Salmonella strains have been isolated that show increased resistance to kanamycin, streptomycin, sulfamethoxazole, tetracycline and amoxicillin-clavulanic among other important antibiotics such as fluoroquinolones and cephalosporins.

Drastical reduction of antibiotics in livestock production

Since the ban of antibiotic growth promoters AGPs in 2006, the countries within the European Union and many others outside the EU, have taken steps to drastically reduce the use of antibiotics in livestock production. Nutritionists have looked for alternatives to antibiotics in an attempt to reduce Salmonella presence during the different stages of pig production life cycle, and therefore reducing the potential risk of prevalence, shedding and enteric diseases in humans.

Feed additive supplementation provide a promising approach to reduce Salmonella colonisation by different modes of action that create a hostile environment for bacterial colonisation of certain (pathogenic) species and a favourable one for beneficial bacteria. In addition, they might strengthen the entire GIT, stimulate the immune system, and modulate gene activity related to virulence or colonisation pathways in bacteria.

Specific characteristics of butyrate

Butyrate, for instance, is a salt of a short-chain fatty acid that is described to downregulate Specific Pathogenicity Island 1 (SPI1) genes inside Salmonella bacteria. This causes a dramatic attenuation of their capacity to invade intestinal epithelial cells and to colonise the intestinal tract in pigs.

In addition, butyrate has been described to trigger the expression of antimicrobial Host Defense Peptides (HDP’s) in the intestinal tract of animals, thereby limiting the growth of several enteric bacterial genera, including Salmonella.

Butyrate supporting swine performance

The Adimix line (Adisseo) consists of butyrate products that support performance and health in swine, by stimulating digestive, immunological and developmental mechanisms in the digestive tract. One product in this line, the product Adimix Precision, has a coating that is capable to deliver butyrate throughout the entire GIT, including the hindgut, where Salmonella resides. This strategy has been shown to reduce Salmonella colonisation in poultry and pigs.

In 2016, a study was published describing a study where the effect was evaluated of feeding late finishing pigs (about 4 weeks before slaughter) with this approach, on Salmonella-challenged commercial pig farms in Ireland.

Figure 1
Probabillity of detecting Salmonella in faeces in both treatment groups

Detecting Salmonella in faeces

The study showed that at day 28 of the trial, the probability of detecting Salmonella in faeces was strongly reduced in the group that received a diet including this additive (30%), compared to the animals from the control group (66%), see also Figure 1. This resulted in a statistically significant reduction of Salmonella seroprevalence at slaughter (Figure 2).

Of note, apart from the effect on Salmonella, an improvement in average daily feed intake (ADFI), average daily gain (ADG) and feed conversion ratio (FCR) was observed in the pigs having received the diet that included the additive (Figure 3). Remarkably, even with a high inclusion level of 3 kg/ton, this led to a positive return over investment (ROI) and gave a feed cost benefit of €0.04/kg live-weight gain.

Figure 2
Seroprevalence (%) at slaughter

Effect in the finisher pig stage

It is important to note that the trial was set up to scientifically evaluate the potential of supplementing a high dosage in the finishing stage only. Other experiments that were conducted in the past, both in institutes and in the field, highlight the extra benefits of administering this product in other stages as well, such as in weaning piglets.

It should be stressed that reduction of Salmonella load from production to slaughter can only be achieved with a comprehensive approach, combining the use of feed additives and the implementation of several hygienic measures and biosecurity protocols. In such a complete Salmonella control program, the additive will be of benefit to decrease the presence of Salmonella inside the animal’s intestinal tract.

Suppressing enteric growth of Salmonella in pigs

In summary, the results from the study presented here are consistent with earlier findings on the capacity of Adimix Precision to suppress enteric growth of Salmonella in animals and under field conditions. As such, it can contribute to food safety during animal production, aside from its well-documented effect on intestinal health and animal performance.

Figure 3
Zootechnical results at end of trial

Tim Goossens, ph.D, Global Technical and Scientific Manager at Adisseo

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