This article discusses the benefits of the use of probiotics, prebiotics and synbiotics in poultry. Experimental reports on their effect on general performance, gut health, and pathogen shedding are reviewed.
The adaptation of chicks to the post-hatch period, along with several stress factors caused by intensive broiler farming, can negatively affect the immune system. This predisposes birds to suffer the colonization of their gastrointestinal tract by pathogenic bacteria, which poses a threat to their health. Among such pathogens, different serovars of Salmonella have been studied. Some serovars produce disease in broilers and hens, whilst zoonotic serovars can also enter the food chain, becoming a public health risk (Humphrey, 2006). The interest has extended to other pathogens such as Campylobacter jejuni and Clostridium perfringens. These bacteria represent an emergent and growing threat to poultry health and performance, and to human health (Humphrey et al., 2007; Van Immerseel et al., 2004).
The possibility of using probiotics, prebiotics, and synbiotics to control infections in the gastrointstinal tract in poultry has been (and still is) intensively researched. In this article, we introduce the topic, review the most relevant publications, and we set the foundations for further reading.
Probiotics can be used to control pathogen shedding in poultry farms, while maintaining a healthy intestinal microbiome. Experiments with probiotics have been carried out to tests their ability to control and reduce the intestinal colonization by Salmonella and other pathogens such as C. jejuni, Listeria monocytogenes, pathogenic E. coli, Yersinia enterocolitica and C. perfringens (Nisbet, 2002; Schneitz, 2005).
B. subtilis is a species of great interest as a poultry probiotic, although not all the strains may be equally effective. It is recommended to choose products that have been developed in a program carried out by probiotic specialists. A large number of scientific studies have showed the efficacy of B. subtilis as a probiotic in broiler diets in both productive performance and promotion of a good health status (e. g. Lee et al., 2013; Latorre et al., 2014; Li et al., 2014; Park and Kim, 2014; Jeong and Kim, 2014).
Sadeghi et al. (2015) examined the effects of a commercial B. subtilis probiotic strain on antibody titers against Newcastle Disease (ND) and Infectious Bursal Disease (IBD). A group of birds were challenged with Salmonella enterica serotype Enteritidis, to represent infectious challenges suffered by the intestine in a pathogen contaminated environment. Birds challenged by Salmonella showed lower antibody titers against ND and IBD, but significant improvement in such titers was observed when a B. subtilis-based probiotic was added to the diet. Infected birds receiving probiotics also have a higher relative spleen weight respect of their counterparts not receiving probiotics. The authors concluded that probiotics have a greater efficacy in the immune response of birds kept in pathogen contaminated environments.
B. subtilis is very effective when pathogens such as Salmonella are present in poultry environments, significantly improving the immune response of the birds.
These results corroborate those observed by La Ragione and Woodward (2003), who administered a B. subtilis spore suspension to specific-pathogen-free broilers before challenging them with S. enteritidis and C. perfringens. The treatment with B. subtilis completely suppressed the colonization and persistence of both pathogens.
Another group of microorganisms frequently used as probiotics in poultry production includes species of lactic acid -producing bacteria. One of these species is Enterococcus faecium, which triggers a lot of interest as a probiotic in the poultry sector. It is applied via drinking water or non-pelletised feeds.
Kralik et al. (2004) observed a significant improvement in the productive parameters of broilers when a E. faecium -based probiotic was applied via drinking water (15 x 10 9CFU/100 L). Also, the addition of the probiotic significantly reduced the intestinal populations of the Enterobacteriaceae family, as well as E. coli, Staphylococcus aureus and E. faecalis.
Subsequently, Capcarova et al. (2010) examined the effects of the same strain of E. faecium and Lactobacillus fermentum (another lactic acid-producing bacterium) on the metabolism and antioxidant status of broilers. The researchers observed that the addition of probiotics to the water reduced blood levels of triglycerides. Also, plasma total antioxidant status of the groups supplemented with one of the probiotics significantly improved compared with the control group. The birds given E. faecium in drinking water showed plasma levels of bilirubin significantly higher than those observed in the control group. The improvement in antioxidant status of the birds leads to mitigation of subclinical inflammatory processes, at both enteric and systemic levels. This can positively affect the productive performance of birds. Therefore, the effects of adding both probiotics to broiler diets would give them a certain anti-inflammatory character that should be considered in some critical moments of the production cycle.
In other scientific studies, the efficacy of different strains of E. faecium have been demonstrated (Weis et al., 2011; Saelim et al., 2012; Cao et al., 2013; Luo et al. 2013). Of special interest is the study conducted by Saelim et al. (2012), who observed the presence of genes encoding enterocin A (a bactericin with selective antimicrobial activity against Listeria) in E. faecium, besides the inhibitory activity of this probiotic against antibiotic-resistant pathogens.
The genus Lactobacillus has also been the object of many studies in domestic birds. Spivey et al. (2014) investigated the epithelial adhesion (in vitro) and the colonization of different species of Lactobacillus spp. (in vivo) in broilers. This study demonstrated that while the adhesion to epithelial cells may be important to predict gastrointestinal colonization, other factors, such as bile tolerance, can also contribute to the colonization by Lactobacillus spp.
Higgins et al. (2008) previously observed that a Lactobacillus probiotic significantly reduced the presence of Salmonella enteritidis in chicks after being infected by the pathogen. In a previous trial, the same researchers (Higgins et al., 2007) observed that this probiotic reduced S. enteritidis concentrations in both cecal tonsils and cecal contents. No relevant results were obtained for S. typhimurium.
An experiment evaluating the probiotic effect of a L. johnsonii strain, fed to day-old chicks as a probiotic, showed that the colonization by E. coli and C. perfringens was significantly reduced by it (La Ragione et al., 2004). In this regard, species of the genus Lactobacillus have also demonstrated their efficacy to reduce mortality due to necrotic enteritis (30% vs 60%), (Hofacre et al., 2003).
Some studies have shown a possible role of Lactobacillus-based probiotics in the prevention of C. jejuni infection (Chaveerach et al., 2004; Fooks and Gibson, 2002; Willis and Reid, 2008). Another lactic acid-producing bacterium is Pediococcus acidilactici, which combined with lactobacilli, has shown to also be an effective probiotic to control C. jejuni (Ghareeb et al., 2012).
The application of probiotics in egg production has also been studied by many researchers. Davis and Anderson (2002) observed that the use a mixed culture of Lactobacillus acidophilus, L. casei, Bifidobacterium thermophilus and Enterococcus faecium improved egg size and reduced feeding costs in laying hens. Furthermore, according to other authors (Kurtoglu et al., 2004; Panda et al., 2008), probiotics can increase egg production and quality.
In recent years, investigations on the role of probiotics in the productive performance and health status of turkeys have generated new contributions that support the use of this type of additive (Wajda et al., 2010; Seifert et al., 2011; Shivaramaiah et al., 2011; Rahimi et al., 2011; Monson et al., 2015).
The application of prebiotics as feed additives for broilers has a shorter story. The number of field trials to evaluate their effects on productive performance, intestinal health, and reduction of pathogen dissemination is increasing.
Xu et al. (2003) observed a dose dependent effect of fructooligosaccharides (FOS) on the daily weight gain. After adding chicory fructans to broiler diets, Yusrizal and Chen (2003) observed an improvement in weight gain, feed conversion and carcass weight. Also, the same authors (Yurizal and Chen, 2003) indicated that dietary fructans supplementation resulted in a higher Lactobacillus count in the gastrointestinal tract, besides a reduction in Campylobacter and Salmonella numbers.
In a study carried out by Sims et al. (2004), turkeys were fed a standard diet supplemented with MOS. An improvement in live weight was observed. Also, Spring et al. (2000) observed that the use of yeast cell wall rich in MOS promoted a reduction of 26% in the intestinal concentrations of Salmonella in broilers.
Thitaram et al. (2005) examined broilers fed diets containing different levels of isomalto-oligosaccharides (OMI). They observed a significant 2-log reduction of the concentration of Salmonella enterica serovar typhimurium in the cecum, besides a significant increase of intestinal bifidobacterial populations. However, the productive performance of the birds did not change significantly when compared with the control group.
Similarly, in a study conducted by Jung et al. (2008), broilers were fed a standard diet containing GOS at two different levels. No effects on live weight, feed intake and feed conversion were observed. However, the study clearly showed a significant increase of intestinal bifidobacterial populations.
Productive performance data in domestic birds, either using probiotics or prebiotics, are often contradictory and mostly dependent on the chosen microorganisms or compounds, the inclusion level, and the period of use. Also, it is essential to consider the hygiene of the facilities and the stress levels of the animals.
Detail of the chicory plant, natural source of inulin
Li et al. (2008) evaluated the addition of FOS and B. subtilis to broiler diets. Improvements in the average daily gain and feed conversion were observed, besides a reduction in the incidence of diarrhea and the mortality rate, compared with the control group.
A considerable increase in the populations of bifidobacteria, lactobacilli and anaerobic microorganisms was observed when supplementing broiler diets with a mix of galactooligosaccharides (GOS) and Bifidobacterium. No effects on live weight, feed consumption and feed conversion were observed (Jung et al., 2008).
Awad et al. (2009) investigated the effects of a dietary treatment including a synbiotic product (a combination of E. faecium and a prebiotic derived from chicory and marine algae) in broilers. The addition of this product to the diet resulted in significant improvements in live weight, average daily gain, carcass yield and feed conversion.
The combined use of probiotics and prebiotics could represent a synergistic strategy to improve the intestinal health of the birds and the pathogen dissemination in the environment, reducing the risk of transmitting food-borne infections to humans.
Further scientific and field trials are needed to determine combinations that are safe and really improve the efficacy of probiotics and prebiotics separately.
Probiotics, prebiotics and synbiotics improve the efficiency of poultry farming, although further scientific investigations and field trials are still necessary.
This article was originally publisehed in nutriNews Spain, with the title Aplicación de probióticos, prebióticos y simbióticos en avicultura
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