L-Carnitine (β-hydroxy-γ-trimethylaminobutyric) is produced in living organisms through food and the biosynthesis of the amino acids lysine and methionine in the liver, kidney, skeletal muscle and brain and then enters the bloodstream. One of the most important functions of L-carnitine in the body is to produce energy, facilitate the entry of long chain fatty acids into the mitochondria, facilitate the exit of short and medium chain fatty acids into the mitochondria, eliminate the toxic effects of acyl groups in cells, regulate the ratio of coenzyme-A versus acyl coenzyme-A in the cytosol and mitochondria.
L-carnitine is a plasma lipid-lowering drug that lowers cholesterol, triglycerides, free fatty acids, phospholipids and low-density lipoproteins, while increases high-density lipoproteins. Supplementation of poultry diets with L-carnitine in has been reported to be effective in controlling blood lipids, abdominal fat pad and poultry health. This study aims to investigate the effects of L-carnitine on growth performance, carcass characteristics, abdominal fat, blood biochemical parameters, immune system, cecal microflora, histology of jejenum, taste properties of breast meat and fatty acid composition of breast meat of broilers.
Material and methods: The experiment was performed in a completely randomized design with 3 treatments, 4 replicates, with 10 broiler chicks with the approximate weights of 45±2g in each pen having the dimension of 1.5×1.5m2 and a total number of 120 chicks during 42 days. The experimental treatments included 3 levels of L-carnitine (0, 200 and 400 mg/kg) in corn-soybean meal basal diet. The effects of experimental treatments were analyzed by SAS software and the comparison of the means with Duncan’s multiple-range test at 5% significance level. Body weight gain, feed intake, and feed conversion ratio (FCR) were calculated at the end of feeding phases to evaluate the traits. European Production Efficiency Factor (Aviagen 2018), carcass characteristics (Farrokhyan et al. 2014), blood parameters (Hosseinitabar et al. 2015), immune system (Seidavi et al. 2014), breast meat fatty acid (Folch et al. 1957) cecal microbial population, histology of the small intestine were calculated at the end of experiment (42 days).
Results and discussion: In the finisher period of the experiment, the chickens fed by a diet containing 400 mg/kg L-carnitine significantly had lower feed intake and FCR as well as the highest weight gain compared to the control (p < 0.05) ). The reason for the increase in weight of the chickens fed by L-carnitine may be due to the effect of this substance on increasing the insulin-like growth factor-I and also the elevated access of chickens to the energy of feed (Kita et al. 2002). Rabie and Szilagyi (1998) reported that the effect of L-carnitine on improving FCR is related to improving nitrogen metabolism. Elevated levels of L-carnitine significantly increased the European Production Efficiency Factor (P <0.05) in which the highest European Production Efficiency Factor (312.75) was obtained by consuming 400 mg/kg of L-carnitine. The application of L-carnitine significantly reduced abdominal fat pad (p < 0.05) and the lowest was obtained by consuming 400 mg/kg L-carnitine. L-carnitine reduces fat accumulation in tissues by altering fat metabolism (Burtle et al. 1994). Heart weight increased and the weight of duodenum decreased with the supplemntation of L-carnitine (p < 0.05). The level of cholesterol, triglycerides, and very low-density lipoprotein (VLDL) decreased with L-carnitine compared to the control (P <0.05). L-carnitine also increased total protein and HDL compared to the control. The effect of L-carnitine on albumin and glucose levels was not significant (P≥0.05). Zhang et al. (2010) reported that L-carnitine reduces blood triglycerides in broilers by increasing the catabolism of fatty acids. On the other hand, Cartwright (1986) believes that L-carnitine reduces the serum triglyceride by increasing the activity of lipase enzyme. The weight of the immune system organs (spleen, thymus, and bursa of Fabricius) were not affected by L-carnitine supplemntation (P≥0.05). The antibody titer against the Newcastle virus and the level of total immunoglobulin against SRBC was significantly increased at 35 and 42 days of age with the use of L-carnitine (p < 0.05). A group of researchers stated that L-carnitine improves the humoral response to vaccination and boosts the immune system in broilers and laying hens by producing monoclonal antibodies and increasing the tendency of white blood cells to remove foreign agents (Mast et al. 2000, Deng et al. 2006). L-carnitine Supplementation of broilers diet significantly (p < 0.05) reduced the population of clostridium, Escherichia coli, coliform bacteria and increased the population of Lactobacillus bacteria The health of digestive system is a necessity to increase performance and profitability in poultry farming. The balance between the gram-positive and negative microbial populations plays an important role in the health of the digestive system. In a healthy digestive system, the population of gram-positive bacteria is predominant (Norreh et al. 2015). L-Carnitine had a positive and significant effect on improving the sensory properties of breast meat (P <0.05) and increased the flavor of breast meat. The highest amounts of oleic acid (18: 1c) and linoleic acid (18: 2c) in breast meat were obtained using 200 and 400 mg/kg L-carnitine, respectively. Also, the length of the intestinal villi increased and the depth of the crypt decreased with increasing L-carnitine level in the diet. L-carnitine appears to improve intestinal histology by affecting the intestine microflora, reducing harmful bacteria, and increasing lactobacilli.
Conclusion: Considering the positive effect of L-carnitine on the traits measured in the present study, supplementing the diet of Ross 308 broiler chickens with 400 mg/kg L-carnitine is recommended to improve growth performance, carcass characteristics, blood parameters, function of immune system, cecal microbial population, histology of the small intestine, and composition of breast meat fatty acids of broiler.