Influence of graded levels ofL-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 ofL-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 ofL-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 mgL-theanine/kg diet; 200LT-basal diet + 200 mgL-theanine/kg diet; and 300LT-basal diet + 300 mgL-theanine/kg diet. Results revealed that the intermediate level ofL-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 allL-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 mgL-theanine/kg diet). Concerning meat color parameters, values for yellowness (b*), and redness (a*) were greater inL-theanine-supplemented groups than the control. Supplementing broiler diet withL-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 ofL-theanine improved antioxidant status in blood by increasing SOD, GSH-Px, and relative CAT levels. It is concluded that the optimum supplementation level ofL-theanine is 200 mg/kg of diet because it resulted in improved performance parameters in broilers. However, higher levels ofL-theanine (300 mg/kg diet) may have deleterious effects on performance and health of broiler chickens. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.