effect of nutrient dilution and glutamine supplementation on growth performance, small intestine morphology and immune response of broilers

introduction glutamine (gln), a semi-essential or conditionally essential amino acid, is an abundant amino acid in plasma and skeletal muscle. it is the main energy substrate for cells that undergo intense replication, such as enterocytes, lymphocytes, macrophages, neutrophils and kidney cells and plays an important role in their function and homeostasis. apart from providing nitrogen for protein synthesis, gln is a precursor for nucleic acids, nucleotides, hexose amines, the nitric oxide precursor arginine (arg), and the major antioxidant-glutathione. it plays a central role in nitrogen transport between tissues, specifically from muscle to gut, kidney, and liver. in addition to its role as a gluconeogenic substrate in the liver, kidney, and intestine, gln is involved in the renal handling of ammonia, serving as a regulator of acid base homeostasis. so the aim of this study was to evaluate the effect of nutrient dilution and l- glutamine (gln) supplementation on growth performance, intestine morphology and immune response of broilers during starter (0 to 10 days), growth (11 to 24 days) and finisher (25 to 42 days) periods. materials and methods a total of 320 one-day-old male ross 308 broiler chicks were randomly assigned to eight treatments with 4 replicates and 10 chicks per each. in this study two levels of nutrient dilution (ross 308 broiler nutrition recommendation and 5% diluted) and 4 levels of gln supplementation (0, 0.5, 1 and 1.5%) were used in a completely randomized design as factorial arrangement 2×4. growth performance was measured periodically. in order to investigate jejenual histomorphology such as villus height, depth of crypt, villus height to depth of crypt ratio, villus width, muscle layer thickness and epithelium thickness, on day 42 after 4 h fasting, one bird per each replicate was randomly selected, slaughtered and 1 cm of middle section of jejenum was cut. cellular immune response was assessed in 40-d-old chick using the in vivo cutaneous basophilic hypersensitivity response lectin phytohaemagglutinin (pha-p) and humoral immune response was evaluated by injection of 1 ml of 10 % suspension of sheep red blood cell (srbc) on day 18. primary immune response was measured after 6 (24 –day-old chick) and 12 (30 –day-old chick) days of the injection and secondary immune response was assessed on day 36 and 42 experiment. results and discussion the results indicated that nutrient dilution and gln supplementation significantly improved feed conversion ratio (fcr) in grower and finisher periods. gln supplementation increased relative weights of jejunum, small intestine, thymus and bursa of fabricius. the nutrient dilution and gln significantly affected villi height and crypt depth of jejunum. gln is an important oxidative fuel for rapidly proliferating cells such as those of the gastrointestinal tract and immune system, reticulocytes, fibroblast. to study humoral immunity, the highest primary and secondary antibody response against sheep red blood cell (srbc) was seen in diets containing 1.5% gln and the lowest was seen in control (without gln supplementation). in cellular immunity determination, 24 h after subcutaneous injection of phytohemagglutinin-p (pha-p) revealed that gln supplementation increased toe web thickness. gln is known to modulate immune function. glutamine is utilized at a high rate by cells of the immune system in culture and is required to support optimal lymphocyte proliferation and production of cytokines by lymphocytes and macrophages. more recently, gln has also been shown to have anti-inflammatory effects, modulating cytokine production, both in vitro and in vivo, possibly through decreasing a major transcription factor regulating immune and inflammatory responses. in addition, it has been demonstrated that glutamine can modulate immune response by t cell activation. therefore the increased toe web thickness after pha-p injection can be explained by increasing t cell proliferation. conclusion the results of present study revealed that formulation of diets with ross 308 nutrient recommendation and 0.5% gln supplementation improved growth performance and enhancement of immune system function was observed in chicks fed diet with 1% gln supplementation and ross 308 nutrient recommendation.