Gut health markers of the efficacy of a probiotic solution in broiler chickens

“The review of the current knowledge of the most relevant gut health biomarkers for poultry production are summarized in this article and effect of the probiotic solution Bacillus subtilis DSM 29784 (Bs29784) on modulating these markers are also highlighted.”

Gut health is a very complex issue involving the microbiota, diet, and host response (inflammation and epithelial integrity). If there is an imbalance in these interactions, inflammation will occur – leading to ‘leaky gut’ (increase of the permeability of the intestinal barrier) and other gut-related disorders. Therefore, biomarkers to evaluate gut health are also difficult to determine with precise accuracy. Nevertheless, biomarkers are necessary to evaluate the intestinal health status, to predict animal performance, to evaluate efficacy of gut health solutions, to be able to justify interventions, and to test dietary strategies and novel diagnostic tools. That is why probiotics are used in poultry nutrition to improve gut health through their influence on microbiota, gut morphology, inflammatory responses, and overall performance.

The gut microbiota derives nutrients from the host’s diet or endogenous secretions, whilst enhancing the diet nutritional value via synthesis of essential nutrients (e.g. vitamins) and the production of complimentary enzymes. For example, gut bacteria produce short chain fatty acids (SCFAs) during the process of degrading dietary polysaccharides.

Common SCFAs produced are acetate followed by propionate and butyrate. Caecal acetate, propionate, and butyrate are undetectable in 1-d-old broilers, but these SCFAs will reach high concentrations in 15-d-old broilers and remain stable afterwards, as the caecal microbiome becomes established. Butyrate or butyric acid is the primary energy source of colonic epithelia and has been shown to be essential to the development of gut villus morphology, which in turn influences host nutrition absorption and immune health.

Gut microbiota interacts directly and indirectly with the intestinal epithelial cells (IEC) that together with a mucus layer functions as the final barrier between the luminal content and the underlying host tissue. There is proven effect of microbiome, especially probiotics on gut integrity, thanks to
• Direct secretion of metabolites and
• Indirect modulation of gut microbiota.

There are many components to maintain intestinal integrity: e.g. tight junctions (TJ), desmosomes, adhesion junctions, and gap junctions.

TJ is a complex of several proteins also known as tight junction proteins that reside in the apical section of the epithelial cell. These proteins include both membrane bound and intracellular proteins that interact between adjacent cells, but also with the cytoskeleton in the cell. This helps stabilising the TJ, but also makes it possible for the cytoskeleton to regulate interactions between IEC.

The review of the current knowledge of the most relevant gut health biomarkers for poultry production is summarized in this article and effect of the probiotic solution Bacillus subtilis DSM 29784 (Bs29784) on modulating these markers are also highlighted.

The first approach is to do the macroscopical scoring of the intestine. Several methodologies exist but the one published by Teirlynck et al (2011) showed negative correlation with villus length and positive correlation with T-cell infiltration in dysbacteriosis condition. In our trial, a dietary challenge was induced by increasing NSP content of the feed with 20% rye inclusion. The Bacterial Enteritis Score was 2.0 for the control group and decreased to 1.0 with the supplementation of Bs29784.

Then, microscopical evaluation (histomorphology) of the gut gives a precise state of the epithelial integrity and inflammation (Gholamiandehkordi et al, 2007). For instance, longer villi height (and then quantity of epithelial cells) is associated with higher body weight (Kraieski et al, 2017). On 42-day-old broilers, Bs29784 significantly increased villi length relative to control from 0.66 to 0.79 µm in the ileum, and from 1.25 to 1.46 µm in the cecum.

Looking at the microbiota from an ecological perspective could provide insight into how to promote health by targeting this microbial community with dietary solutions. Microbiota will be as resilient as possible if the population is diverse and contains more bacteria with anti-inflammatory properties (butyrate producers like Ruminococcaceae and Lachnospiraceae) and less opportunistic pathogens like Clostridium perfringens or Enterobacteriaceae (Salmonella or Escherichia coli). In a necrotic enteritis challenge model, Bs29784 group showed higher alpha-diversity than control birds with Chao and Shannon index. We also observed higher prevalence of Ruminococcaceae (P>0.001) with the supplementation of Bs29784, especially for Faecalibacterium prausnitzii (+13.4%; P<0.001) that is known to be correlated with other gut health parameters such as villus length and CD3 area. In another trial where broilers were challenged with C. perfringens, we observed that the number of E. coli at 21 d and the number of C. perfringens at 28 d were significantly reduced in the Bs29784 group.

Finally, some microbial metabolites can be linked to gut health. Nicotinic acid for instance activates the GPR109A receptor, which suppresses intestinal inflammation. We demonstrated that it increases cell proliferation and wound healing in a Caco-2 in vitro model. An exploratory study on 13-day-old chicks showed that Bs29784 increased (P <0.01) the intestinal content of nicotinic acid in ileum and jejunum, revealing a mode of action through which it can improve gut health.

This showed some very important gut health biomarkers that could be used for both research and practical purposes. We also demonstrated that these key markers can be measured to evaluate the consistent efficacy of Bs29784 in broilers.