Effect of dietary L-glutamine on growth performance, blood parameters, carcass quality, and immune response in broiler chickens

Introduction: Glutamine represents approximately 30-35% of the total amount of nitrogen in the blood derived from amino acids. The role of glutamine as a nitrogen shuttle helps to protect against the toxic effects of high levels of ammonia in the blood. In addition, glutamine has vital and specific metabolic functions as a vehicle for carbon exchange between tissues, as a fuel for rapid cell division, and as a precursor of many naturally active molecules. It's a great example of how amino acids are used for different purposes in the metabolism and the immune system of the body. Glutamine, a conditionally essential amino acid, seems to be a key nutrient for the gut, as it may be a prominent source of vitality for the enterocytes. Glutamine appears to trigger an increase in the level of intestinal secretory immunoglobulin A, which is essential for mucosal defense. The investigation showed that the use of amino acid supplements in broiler diets improves the performance and the carcass characteristics. Glutamine is one of the most abundant amino acids in blood plasma and is involved in the building of muscle, and tissue, and gaining body weight. Researchers found that adding 10 g of L-glutamine per kg of food increased the weight gain and serum immunoglobulin A and G concentrations in broiler chickens. Therefore, an experiment was carried out in broiler chickens over 42 days of production to determine the effect of L-glutamine on broiler growth, carcass quality, and certain blood parameters. Materials and methods: The experiment was conducted using 300 one-day-old male Ross 308 broiler chickens in a completely randomized design with five treatments and five replicates from the age of 1 to 42 days. The experimental treatments included were: the addition of zero, 0.25, 0.5, 0.75, and 1% of L-glutamine in corn-soybean meal-based diets supplemented with dietary fat. During the experimental period, average daily feed intake (DFI), body weight gain (BWG), and feed conversion ratio (FCR) were measured. At the end of the experiment, two birds were selected from each replicate and slaughtered after weighing, and the weight of the internal organs (thigh, breast, heart, liver, gizzard, fat pad, pancreas, bursa, spleen, and thymus) was measured. Blood samples were collected from two birds per replicate to determine the number of white blood cells (WBC), and heterophile to lymphocyte ratio (H/L). Blood samples were taken from the jugular vein in tubes without anticoagulant and then centrifuged (2000×g for 10 min) to obtain a serum. On the 42nd day of rearing, serum cholesterol (total cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL)) and triglycerides were determined by calorimetric examination. Results and discussion: Weight gain during the initial and growth periods was affected by L-glutamine supplementation (P<0.05). Despite higher feed intake for L-glutamine-supplemented diets during the initial period, this effect was significant only during the growth period (P<0.05). FCR and relative weight of internal organs, except liver weight, were not significantly different from the control group in the L-glutamine-supplemented chickens. The addition of 0.5% L-glutamine supplementation reduced cholesterol and triglyceride content and increased HDL in the blood of broilers (P<0.05). The H/L ratio in chickens that consumed L-glutamine was significantly lower than in the control group (P<0.05). L-glutamine has been reported to increase the activity of the intestinal enzyme Na-K ATPase, thereby indirectly increasing the absorption capacity of nutrients such as glucose and amino acids in the intestine. Researchers reported that L-glutamine increases the performance and feed intake of chickens by improving intestinal function and increasing digestibility. Expanding the villi of the small intestine can increase digestion and feed intake by increasing nutrient absorption and thus improving chicken performance. Improving the morphology of the digestive system is one of the possible mechanisms of the positive effect of L-glutamine on improving weight. Since glutamine stimulates anabolic conditions in the body and increases the amount of protein synthesis, therefore, along with muscle growth, it can increase the final body weight. Avian health is directly related to the immune system, and birds with adequate immune systems grow better. The majority of essential amino acids are recognized as critical resources for cytokine production and immune function. Conclusions: Results from this study indicate that 0.5% dietary glutamine supplementation improved growth performance and had a positive effect on lipid metabolism-related blood parameters.