16S ribosomal RNA sequencing reveals a modulation of intestinal microbiome and immune response by dietary L-theanine supplementation in broiler chickens.

Despite the availability of abundant literature on green tea, studies on the use of L-theanine (an amino acid found only in green tea) as a feed additive in poultry especially broiler are limited. So, this study was conducted to explore the effects of L-theanine on the intestinal microbiome and immune response in a broiler. A total of 400-d-old chicks were randomly divided into four treatment groups (A, B, C, and D) using a complete randomized design. Treatments were as follows: A, control (basal diet); B, basal diet + 100 mg L-theanine/kg diet; C, basal diet + 200 mg L-theanine/kg diet; and D, basal diet + 300 mg L-theanine/kg diet. Mucosal samples from ileum and jejunum of broiler chicken were extracted at 21 and 42 d of age. Extraction of genomic DNA was followed by amplification of V3 and V4 hypervariable regions of 16S ribosomal RNA. After Illumina sequencing, results revealed that treatment with L-theanine significantly increased the population of Lactobacillus in ileum and jejunum as compared to a control group, but the higher population was observed in jejunum at both 21 and 42 d of age. The overall diversity of the jejunum microbiome in the treatment group was significantly lower than that of the ileum and control group (P < 0.05). Results of this study revealed that mRNA expression of TLRs (TLR-2 and TLR-4) and cytokines (TNF-α, IFN-γ, and IL-2) was decreased in response to treatment with L-theanine. Moreover, the negative correlation of abundance of Lactobacillus was observed with expression of IL-2 and IFN-γ in the intestine and these effects were highly significant (P < 0.01). In summary, our finding revealed that dietary supplementation of L-theanine exhibited a positive influence on intestinal bacteria by supporting beneficial microbes like Lactobacillus while decreasing harmful microbes like Clostridium.

Influence of Graded Levels of l-Theanine Dietary Supplementation on Growth Performance, Carcass Traits, Meat Quality, Organs Histomorphometry, Blood Chemistry and Immune Response of Broiler Chickens.

l-theanine is a water-soluble non-proteinous amino acid mainly found in green tea leaves. Despite the availability of abundant literature on green tea, studies on the use of l-theanine as a feed additive in animals, and especially broilers are limited. The objective of this study was, therefore, to evaluate the effect of different dietary levels of l-theanine on meat quality, growth performance, immune response, and blood metabolites in broilers. A total of 400 day-old broiler chicks were randomly divided into four treatment groups using a completely randomized design; C-control, basal diet; 100LT-basal diet + 100 mg l-theanine/kg diet; 200LT-basal diet + 200 mg l-theanine/kg diet; and 300LT-basal diet + 300 mg l-theanine/kg diet. Results revealed that the intermediate level of l-theanine (200 mg/kg diet) showed better results in terms of body weight gain (BWG), feed consumed (FC), and feed conversion ratio (FCR) as compared with the other supplemented groups and the control. The live weight eviscerated weight and gizzard weight were higher in all l-theanine levels as compared to those of the control group. Increased weight (p ≤ 0.05) of spleen and bursa were found in group 200LT (200 mg l-theanine/kg diet). Concerning meat color parameters, values for yellowness (b*), and redness (a*) were greater in l-theanine-supplemented groups than the control. Supplementing broiler diet with l-theanine reduced (p = 0.02) total serum cholesterol contents while increased HDL. Further analysis revealed lower relative serum cytokines (IL-2 and INF-γ) and reduced mRNA expression of TNF-α and IL-6 in thymus, and IFN-γ and IL-2 in spleen in the treated group. Moreover, supplementation with 200 mg/kg of l-theanine improved antioxidant status in blood by increasing SOD, GSH-Px, and relative CAT levels. It is concluded that the optimum supplementation level of l-theanine is 200 mg/kg of diet because it resulted in improved performance parameters in broilers. However, higher levels of l-theanine (300 mg/kg diet) may have deleterious effects on performance and health of broiler chickens.