Gut health is usually considered as the symbiotic relationship between the host and its microbiota. Recent research has proposed a four-pillar scheme to describe healthy, pre-disease and disease states from dynamic interactions among the microbiota, mucosal barrier, immune system and redox balance (van de Gutchte et al., 2018) (Figure 1).
In case of an imbalance in these interactions, inflammation will occur, leading to 'leaky gut' – increased permeability of the intestinal barrier, and other gut-related disorders. Nowadays, probiotics are gaining importance as nutritional strategies to improve gut health through their influence on microbiota, gut morphology, inflammatory responses and overall animal performance.
Probiotics for gut health
Probiotics are live microorganisms, when administered in adequate amount, can confer beneficial physiological effects to the host (WHO, 2001). Probiotics can improve intestinal microbiota balance, leading to an optimum environment for digestion and nutrients absorption. These more balanced microbiota will also help to reduce the growth and/or the pathogenicity of harmful bacteria and positively influence the host immune system, contributing to overall better animal health and performance. Compared with antibiotics which have a specific effect on pathogens and maybe some anti-inflammatory properties, probiotics instead can deliver global benefits to the host through multiple and complementary modes of action.
In this article, recent trials with a poultry specific probiotic solution, unique spore forming Bacillus subtilis (strain DSM 29784, Alterion®) are presented. This unique specific strain was discovered and selected after extensive in vitro research at Novozymes's Laboratories, followed by further in vivo research in independent scientific institutions, universities and Adisseo' research farm (CERN, Centre for Expertise and Research on Nutrition). With all efforts above, Alterion is proved to deliver consistent benefits for poultry production from its research-supported modes of action, including positive changes in the microbiota, intestinal integrity and inflammatory responses. As such, Alterion enhances dialogues between the microbiota and the host, creating sustainable effects.
The balanced and varied microbiota is key to develop and maintain robust gut functions. The effect of Bacillus subtilis on bacterial species in the gut of broilers was investigated at Southern Poultry Research, Inc (Athens, GA, USA) in collaboration with Dr Greg F. Mathis. In a 42-day trial, 1600 Cobb 500 male broiler chicks were fed a control or treatment diet with Alterion supplemented at 1x108 CFU/kg of feed. At day 42, intestinal contents were sampled to determine ileal and cecal microbiota composition by rRNA gene sequencing.
Figure 2. Effect of Alterion on the abundance of different taxonomic groups of the gut microbiota - from cecal samples of 42-day-old broilers
In addition, increased relative abundance of Lachnoclostridium was also observed. These bacteria degrade oligosaccharides and produce short chain fatty acids (SCFAs) – butyrate in particular. It is well known that as a very important microbial metabolite, butyrate represents the main source of energy for enterocytes, cells from gut wall, and a very potent anti-inflammatory compound at the same time.
Pillar 2 – Improved gut mucosa and Tight Junction
The gut mucosa, or alternatively named gut barrier or frontier, is where many dynamic interactions occur between the host and the "outside environment". The integrity and robustness of gut mucosa is essential for efficient nutrients absorption, innate immune system stimulation and prevention of bacteria and toxins from entering the bloodstream, therefore accounting for the optimal bird health and performance.
Figure 3. Effect of Alterion on microvilli length (µm) in the ileum and cecum of broilers (* P<0.001)
In addition to longer microvilli, Alterion also has direct positive influence on the intestinal barrier integrity, demonstrated by an in vitro model (Caco-2 monolayer cells in Transwell System). A pro-inflammatory cytokine (TNF-α) was introduced to impair intestinal frontier integrity. Transepithelial electrical resistance (TEER, voltage between the apical and basolateral side) was measured, corresponding to the passage of the molecules. The higher the TEER, the better the integrity. In addition, paracellular pathway with D-mannitol was also monitored to further evaluate the integrity of the intestinal barrier. More D-mannitol passing from apical to basolateral means that the integrity of the barrier is damaged.
Pillar 3 – Reduced inflammatory responses
Probiotics have been recognized and widely used as one of most effective AGP alternative solutions. In order to check their direct anti-inflammatory properties, the same in vitro model as above is used. Alterion was tested and compared with two other Bacillus subtilis strains found in commercial probiotic products (named Bs A and Bs B), benchmarked by epigallocatechin gallate (EGCG) as strong anti-inflammatory compound.
Figure 5. Caco-2 cells IL-8 production under IL-1 stimulation (+ negative and positive controls)
In the broiler study mentioned previously, Alterion supplementation led to a 5.4% improvement in FCR, 5.7% increase in final body weight and an unchanged feed intake in growing broilers (Table 1). These economically important parameters are therefore greatly influenced by gut health, through in particular changes in the gut microbiota and mucosa.
As summary, Alterion, when administrated to broilers, improves the microbiota balance, strengthen mucosal barrier function and prevent inflammation, which all together contribute to a healthier gut and optimal bird performance.
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Article made possible through the contribution of Vincent Jacquier and Damien Prévéraud (Adisseo France S.A.S.) and Sumit Saxena and Claire Xu (Adisseo Asia Pacific)