Feed additives’ role in reducing Salmonella in poultry

The presence of Salmonella in poultry is a costly occurrence for producers. Feed additives can help in a variety of ways to reduce the risk of Salmonella infections. Essential oil compounds’ antibacterial properties support good flock health and contribute to consumer food safety.

By Armin Vikari, Danisco Animal Nutrition

Although Salmonella is susceptible to antibiotics and it might seem a quick and sensible solution to the problem, the use of antibiotics routinely in animal production is controversial and not thought to be a sustainable method of ensuring food safety for the consumer. One reason for this is the impact that prolonged use of antibiotics is thought to have on encouraging bacterial resistance. Coupled with this is the consumers’ negative perception of medication in the food chain and their demand for antibiotic free ‘healthy’ nutrition.

Unfortunately, despite the drive to use antibiotics only when necessary and at therapeutic concentrations, there is increasing antimicrobial resistance within Salmonella and its prevalence and virulence is continuing to be a major challenge worldwide. A 2010 survey by Foodborne Diseases Active Surveillance Network indicated that while infection rates of E.Coli are declining, incidences of Salmonella infection is relatively stable; emphasising the persistence of Salmonella.

Therefore, more efficient measures, focusing on the whole poultry production chain as well as the subsequent storage and handling of meat, need to be implemented to prevent transmission of Salmonella to humans. By using a multi-factorial approach with products that create a hostile environment for pathogen proliferation, while ensuring the cultivation of beneficial microbial populations and healthy flocks, it is possible to reduce the risk of Salmonella infection and contamination without resorting to antimicrobials.

Controlling Salmonella prevalence

Salmonella are carried within the gut of the birds and are shed from the infected bird through faeces, feather dust, and secretions from the eyes and nose contaminating the environment. During post-slaughter processing, Salmonella can be transferred between carcasses by faecal or digesta contamination; by cross-contamination of carcasses in the rinse/ chill cycles, or on equipment surfaces. In processing facilities, strict hygiene practices are essential to limit the risk of bacterial spread.

At farm level, vermin control and regularly refreshed foot baths should be mandatory. Disinfectants, such as Virkon® S, that have rapid action in the presence of organic matter and are proven to reduce the potential infectivity of resistant Salmonella super-strains (S.enteritidis, S.typhimurium, S.hadar) are most effective.

Within flocks, vaccination and maintenance of clean, healthy birds reduces the likelihood of bacteria prevalence. Environmental conditions play an important role in flock health and using appropriate feed additives to optimise the birds’ intestinal microflora and digestion, improves nutrient utilisation resulting in healthier birds, better performance and litter conditions.

Implementation of the measures mentioned above prevents bacterial proliferation within the flock and the environment; minimising the risk of Salmonella infection. Reducing and preventing Salmonella infection in poultry, and throughout the food chain, will reduce incidences of Salmonellosis in humans.

The role of innovative feed additives

Many feed additives are capable of reducing pathogenic challenges, maintaining bird’s performance and reduce the risk of costs associated with infected stock treatment or flock euthanasia. Innovative feed additives including probiotics (direct-fed microbials) and phytogenics, such as essential oil compounds, are known to beneficially modulate the intestinal microflora improving intestinal health and nutrient utilisation. They also have been shown to support a healthy immune function, which subsequently improves concurrent pathogen resistance of the poultry.

The use of probiotics

Probiotics are micro-organisms which aid in establishing and maintaining a well balanced microbiota in the gut. The development of the gut microbiota balance in the first few days post-hatch is the key to efficient nutrient utilisation by the bird and resistance to enteric disease caused by pathogenic bacteria invading the gut. An unfavourable balance of the gut microbiota will have a negative impact on subsequent bird health and performance.

Supplementation of poultry diets with probiotics beneficially alters the gut and the litter microbiota composition. Probiotic Bacillus subtilis strains can benefit intestinal morphology, suggesting increased capacity for nutrient absorption by the bird. Therefore the use of probiotics can help support a more efficient nutrient utilisation and better flock health status. Positive effects on litter quality encourage a cleaner flock environment, help reduce the risk of contamination of the end product and decrease the occurrence of carcass blemishes. This results in improved quality and increased safety of the end product.

Antibacterial effects of essential oils

Combinations of plant extracts or essential oil compounds, also referred to as “Phytogenics”, are incorporated into diets to improve the productivity of livestock through improvement of feed intake, promotion of the animal’s production performance, and improving the quality of food derived from those animals.

In addition to this, numerous plant or essential oil compounds have shown effective antibacterial, anticoccidial, antifungal, or antioxidant properties. Within the range of essential oil compounds used, carvacrol, thymol and cinnamaldehyde found in oregano, thyme and cinnamon respectively, are probably used most frequently. These have been shown to have strong antibacterial and antioxidative properties (Table 1).

Although differing in their mechanism of action - cinnamaldehyde is an aliphatic aldehyde, whereas carvacrol and thymol are phenolic compounds - these compounds disturb the integrity and function of bacterial cell membranes. In vitro studies have shown these phytogenics as having a broad spectrum activity against pathogenic gram negative bacteria E. coli and Salmonella and the gram positive Clostridium bacteria.

These observations have been supported by a recent review of increasing amounts of in vivo data. In addition, a recent study showed that a combination of cinnamaldehyde and thymol added to a wheat-soybean based diet reduces the proportion of gram-negative pathogenic bacteria E.coli and Salmonella in the caecum of male broilers.

Efficacy of enzymes and essential oil compounds

Non starch polysaccharide (NSP) enzymes have traditionally been used to improve nutrient digestion and reduce digesta viscosity. Improvement in nutrient digestion reduces the likelihood of the proliferation of pathogenic bacteria in the gut of poultry, with consequent benefits to gut health. Several studies found beneficial gut health effects from using NSP enzymes in the diet.

A recent study at Southern Poultry Research USA*, used a combination of two essential oil compounds, cinnamaldehyde and thymol, on top of xylanase. The results indicated that xylanase enzyme and essential oil compound supplementation improved 42d bodyweight gain and feed efficiency and the effect of the combination was greater than using each additive individually. Xylanase enzyme and essential oil compound supplementation individually reduced (P<0.05) the incidence of Salmonella infection in the intestine between birds by 61% and when used in combination, by 77%, compared to control.

Lower feed costs (€0.54) per kilo of gain were seen when both the xylanase and essential oil products were used in combination, compared to the control animals (€0.629) and the individual additives (€0.591 for essential oils, €0.552 for xylanase). The data also suggest that dietary addition of a selected combination of essential oil compounds and enzymes can contribute positively to food safety by reducing horizontal transmission of Salmonella in poultry production systems.

In addition, poultry fed additives such as these, can go straight to slaughter and do not require a withdrawal period, saving time and money for the producer and reducing complication at the feed mill.

In conclusion one may state that healthy nutrition solutions involving probiotics, enzymes and essential oil compounds for poultry production systems can promote healthier animals and reduce treatment costs, leading to better profits for the producers and safer food for the consumer.

Virkon® S is a trademark and registered trademark of DuPont or its affiliates.

*More information available on request from Danisco Animal Nutrition, Marlborough, UK