There are well documented complications associated with the continuous use of antibiotics in the poultry industry. Over the past few decades, probiotics have emerged as viable alternatives to antibiotics; however, most of these candidate probiotic microorganisms have not been fully evaluated for their effectiveness as potential probiotics for poultry. Recent evaluation of a metagenome of broiler chickens in our laboratory revealed a prevalence of Lactobacillus reuteri (L. reuteri) and Actinobacteria class of bacteria in their gastrointestinal tract. In this study Lactobacillus reuteri and Streptomyces coelicolor (S. coelicolor) were selected as probiotic bacteria, encapsulated, and added into broiler feed at a concentration of 100 mg/kg of feed. In an 8-week study, 240 one day-old chicks were randomly assigned to four dietary treatments. Three dietary treatments contained two probiotic bacteria in three different proportions (L. reuteri and S. coelicolor individually at 100 ppm, and mixture of L. reuteri and S. coelicolor at 50 ppm each). The fourth treatment had no probiotic bacteria and it functioned as the control diet. L. reuteri and S. coelicolor were added to the feed by using wheat middlings as a carrier at a concentration of 100 ppm (100 mg/kg). Chickens fed diets containing L. reuteri and S. coelicolor mixture showed 2% improvement in body weight gain, 7% decrease in feed consumption, and 6–7% decrease in feed conversion ratios. This research suggests that L. reuteri and S. coelicolor have the potential to constitute probiotics in chickens combined or separately, depending on the desired selection of performance index.

The research involving the beneficial aspects of amino acids being added to poultry feed pertaining to performance, growth, feed intake, and feed conversion ratio is extensive. Yet currently the effects of amino acids on the gut microbiota aren’t fully understood nor have there been many studies executed in poultry to explain the relationship between amino acids and the gut microbiota. The overall outcome of health has been linked to bird gut health due to the functionality of gastrointestinal tract (GIT) for digestion/absorption of nutrients as well as immune response. These essential functions of the GI are greatly driven by the resident microbiota which produce metabolites such as butyrate, propionate, and acetate, providing the microbiota a suitable and thrive driven environment. Feed, age, the use of feed additives and pathogenic infections are the main factors that have an effect on the microbial community within the GIT. Changes in these factors may have potential effects on the gut microbiota in the chicken intestine which in turn may have an influence on health essentially affecting growth, feed intake, and feed conversion ratio. This review will highlight limited research studies that investigated the possible role of amino acids in the gut microbiota composition of poultry.

The continuous use of antibiotics is associated with many complications in the poultry industry. Probiotics have emerged as a viable alternative over the past few decades to counter the adverse effects of antibiotics. No candidate probiotic microorganisms have been fully evaluated in the poultry industry for their effectiveness as potential probiotics in guinea fowls (GFs) compared to chickens. Recently, a metagenome evaluation of GFs in our laboratory revealed a predominance of Lactobacillus reuteri (L. reuteri) and actinobacteria class of bacteria in their gastrointestinal tract. The aim of this study is to evaluate a well-known lactic acid probiotic bacterium (L. reuteri) and a unique probiotic (S. coelicolor) that has not been assessed in any guinea fowl species. In the current study, L. reuteri and Streptomyces coelicolor (S. coelicolor) were selected as probiotic bacteria, encapsulated, and added into French guinea fowl (FGF) feed individually at a concentration of 10⁸ cfu/g or both microorganisms combined each at 10⁴ cfu/g. In an 8-week study, 216-day-old guinea keets were randomly assigned to four dietary treatments as indicated: (1) L. reuteri (10⁸ cfu/g); (2) S. coelicolor (10⁸ cfu/g); (3) mixture of L. reuteri (10⁴ cfu/g) and S. coelicolor (10⁴ cfu/g); and (4) control treatment (no probiotics included). The L. reuteri, S. coelicolor, and L. reuteri + S. coelicolor were added into the feed using wheat middlings as a carrier at a final concentration of 10⁸ cfu/g. The FGFs that were fed diets containing L. reuteri showed improved feed consumption at 3–8 weeks of age (WOA). The guineas fed L. reuteri and S. coelicolor showed a lower feed conversion ratio (FCR), which was significant at 2 and 8 WOA, and a numerically lower 8-week average FCR when compared with other dietary treatments. Differences in body weight gain among all dietary treatments were not significant. This research suggests that L. reuteri and S. coelicolor may have the potential for use as probiotics in FGFs when used in combination or separately.

The overuse of antibiotics in poultry production has raised global concerns on antimicrobial resistance thereby increasing the need for effective and sustainable alternatives such as probiotics. Although previous research reveals that Lactobacillus reuteri and Streptomyces coelicolor supplementation improves performance metrics in broiler chickens, the molecular mechanisms contributing to these outcomes remain unclear. The goal of this study was to assess the transcriptomic and metabolomic responses of broiler chickens fed diets supplemented with L. reuteri, S. coelicolor, or their combination. A total of 240-day-old broiler chicks were randomly assigned to four dietary treatments and raised under standard commercial conditions for eight weeks. Liver and intestine samples collected at weeks 4 and 8 were subjected to RNA isolation, sequencing and differential gene expression analysis. Transcriptome profiling revealed unique gene expression patterns associated with each probiotic treatment and organ. Functional enrichment analyses highlighted the modulation of key immune pathways including cytokine signaling and lymphocyte activation, as well as metabolic pathways related to lipid processing and electrolyte balance. Metabolomics revealed that the combination treatment produced the largest unique number of detected metabolites. Together, we demonstrate that the combination of L. reuteri and S. coelicolor induced a synergistic transcriptional and metabolomic response that affects both immune regulation and nutrient metabolism. These findings provide insight into the host-probiotic interaction at the molecular level and support the potential use of targeted probiotics as functional feed additives in poultry.