Nutritional additives to enhance gut microbiome and immunity
In modern-day intensive broiler production systems, strategies to improve broiler immunity and gut health are crucial, particularly amidst antibiotic growth promoter restrictions. Focusing on nutritional additives, this report elaborates on the benefits of supplementing broiler diets with selenium-yeast, fenugreek seeds, and Bacillus-based probiotics on gut health and immunity.
Enteric diseases can cause an imbalance of the intestinal microbiota, which can result in dysbiosis, inflammation, and susceptibility to other pathogens. There is, therefore, a great need to find effective and sustainable strategies to improve broiler immunity while enhancing the intestinal microbiota balance, especially in the face of the ban or restriction of antibiotic growth promoters (AGP) in many countries.
The additives
Researchers of the current study published in the journal The Microbe explored the effect of supplementing different dosages (0.15, 0.225 and 0.30 mg/kg) of selenium-enriched yeast (selenium-yeast) on growth performance, intestinal morphology, gut microbial population and immune status of broiler birds (day 1-35). The other part published in the journal Poultry Science explores the effects of combining fenugreek seeds and multi-strain Bacillus-based probiotics on the immune-related gene expression and caecal microbiome in broiler chickens (day 1-42); the multi-strain Bacillus-based probiotics contained B. subtilis, B. amyloliquefaciens, and B. licheniformis.
Selenium (Se) is an essential element for poultry production; its inadequacy may lead to poor growth performance, nutritional muscular dystrophy, immune deficiencies, reduced antioxidant status and lipid peroxidation. Yeast and yeast cell wall products modulate the host immune response, reduce the load of pathogens, and ameliorate the pathologic effects of enteric infections in poultry. The principal mechanisms of action of yeast probiotics and prebiotics are competitive exclusion and antagonism, immunomodulation, effect on digestive enzymes, and direct nutritional benefits. Yeast cells are capable of binding dietary selenium in the form of both organic and inorganic compounds.
As a phytogenic additive, Fenugreek seeds contain various bioactive compounds, such as saponins, flavonoids, alkaloids, and polyphenols, that can exert antioxidant, anti-inflammatory, antimicrobial, and immunomodulatory effects. Fenugreek seeds also contain insoluble and soluble fibres, with high concentrations of galactose and mannose — presenting a potential beneficial effect on gut microbiome. Direct-fed microbials or probiotics are feed additives containing live or viable microorganisms that can confer beneficial effects on the host animal; for example, Bacillus spp. can modulate the intestinal microbiota by producing antimicrobial substances, enzymes, and organic acids, as well as competing with pathogens for nutrients and adhesion sites.
Selenium-yeast on growth performance
Supplementation of selenium-yeast (Se-Ye) at different dose rates significantly improved weight gain and the feed conversion ratio (FCR) compared to the control group birds (Table 1). The highest dosage (0.30 mg/kg Se-Ye) showed the greatest improvement in growth performance.
Intestinal morphology and immunity
The results of the study demonstrated improvement in intestinal morphology and immunity of birds supplemented with selenium-yeast. The height of the villi and crypts depth and their ratio were highly significant amongst the selenium-yeast groups with the 0.30 mg/kg dosage producing the best results (highly enhanced surface area for nutrient absorption). The occurrence of goblet cells was higher in the selenium-yeast-fed birds. Goblet cells are specialised epithelial cells that have a role in barrier maintenance through the secretion of mucus. In addition, goblet cells secrete anti-microbial proteins, chemokines, and cytokines demonstrating their function in innate immunity beyond barrier maintenance.
Supplementing selenium-yeast increased the weight, length and thickness of immune organs, that is, the bursa of Fabricius, spleen and thymus, indicated enhanced immunity. Selenium-yeast at 0.225 and 0.30 mg/kg also boosted the humoral immunity against Newcastle disease virus compared to the unsupplemented diet. The researchers also concluded that suppression of inflammatory factor, interleukin 10 (IL 10) is selenium-yeast dose-dependent. “This means beneficial bacteria might take part in anti-inflammatory reactions that minimise inflammation or decrease cytokine secretion by suppressing the pathogenicity of pathogens,” the researchers said.
Selenium-yeast on microbial population
From the analysis of the caecal microbial population, Ileal and colorectal microbial population and faecal microbial population, the researchers found a selenium-yeast dose-dependent reduction of gut pathogens (E. coli and Salmonella), while the abundance of the beneficial bacteria, Bifidobacterium spp., was significantly increased compared to the birds from the control diet.
Fenugreek seeds and probiotics on immune modulation
The relative mRNA expression of ileal pro-inflammatory interleukins IL6 and IL8L2 showed significant downregulation by the individual supplementation of fenugreek seeds, Bacillus-probiotics and their combination compared to the control diet. The researchers stated that the downregulation of IL-6 and IL8L2 is generally associated with an anti-inflammatory response. They said previous studies have shown the upregulation of IL-6 and IL8L2 in chickens is associated with Salmonella and Eimeria infection. “The observed downregulation of IL-6 and IL8L2 in our study suggests that both fenugreek seeds and multi-strain Bacillus-probiotics exert anti-inflammatory effects in the gut.”
To substantiate their observation, researchers also assessed the gene expression of other pro-inflammatory-related factors (caspase-6, interferon regulatory factor 7 and β-Defensins) and found a similar trend whereby the individual supplementation of fenugreek seeds, Bacillus-probiotics and their combination significantly downregulated these indicators of inflammation compared to the control diet. There was a tendency for improved gut microbiome diversity following the combination of the additives, which was ascribed to the additive effects of the prebiotic fenugreek seeds and the Bacillus-based probiotics.
Synergistic effect
It was concluded that supplementation of selenium-enriched yeast at the dose rate of 0.30 mg/kg significantly improves the growth performance, and gut health and enhances the immunity of broiler chickens. On the other hand, both fenugreek seeds and multi-strain Bacillus-based probiotics demonstrate the potential for improving broiler immunity through inflammation reduction. “The combination of fenugreek seeds and Bacillus-based probiotics offers a synergistic effect in immune modulation and specific microbial modulation, warranting further investigation with pathogen challenge models for comprehensive understanding,” the researchers said.
