effect of different levels of vitamin c and l-carnitine on performance and some blood and immune parameters of broilers under heat stress.

introduction: high environmental temperature during summer months which leading to heat stress, is of great concern in all types of poultry production. feed consumption, growth rate, hatchability, mortality, and other important traits governing the prosperity of the industry are adversely affected by severe heat stress. literature suggests that the advantages of dietary l-carnitine and ascorbic acid have been particularly apparent under heat stress (8). l- carnitine is a zwitterionic compound synthesized in vivo from lysine and methonine, and is essential for the transport of long – chain fatty acid across the inner mitochondria membrane for β – oxidation and remove toxic accumulations of fatty acids from mitochondria (18). vitamin c is an effective antioxidant, which is essential for collagen synthesis, helps to maintain various enzymes in their required reduced form, and participates in the biosynthesis of carnitine, norepinephrine and certain neuroendocrine peptides (11). invertebrates, insects, most fishes, some birds, guinea-pigs, bats and primates are not able to synthesize ascorbic acid. thus, these animals must depend upon a dietary supply of this vitamin c. in poultry, ascorbic acid has been demonstrated to be essential for growth (25). materials and methods: in this study, 396 of ross 308 broiler chicks in a completely randomized design with 3 × 3 factorial arrangement with 4 replicates of 11 chicks in each replicate were used for 42 days. treatments were 3 levels of vitamin c (0, 250 and 500 mg/ kg) and 3 levels of l-carnitine (0, 50 and 100 mg kg). in the first 3 weeks of breeding, broilers were under normal temperature and heat stress was done from the beginning of forth week. feed and water were provided ad-libitum. performance parameters were recorded weekly. the 0.5 ml suspension of 5% srbc was injected at 28 and 35 days of age in one bird of each pen. to determine the antibody titer, blood was collected 1 week after each injection. vaccination against newcastle was done at 8 days of age and 10 days after that blood was collected for determining newcastle titer. at the end of the experiment, one bird of each replicate was slaughtered and blood was collected for analyzing lipid parameters, and also carcass characteristics were analyzed. results and discussion: highest feed intake observed in birds that consuming 250 mg/kg of vitamin c and 100 mg/kg of l-carnitine at the starter period but at the grower period feed intake was highest in birds consuming 500 mg/kg of vitamin c and 50 mg/ kg of l-carnitine. in the total period of experiment, treatments of 500 mg/kg of vitamin c with 50 and 100 mg/kg l-carnitine showed highest feed intake (p 0/05). celik and ozturkcan (8) showed that l-carnitine or l-carnitine and vitamin c improved feed conversion ratio. the lowest concentration of triglycerides and ldl and the highest concentrations of blood hdl was observed in birds consuming 500 mg/kg vitamin c and 100 mg /kg of l-carnitine (p<0.05). the lowest concentration of cholesterol was observed in birds consuming 500 mg/kg vitamin c and 100 mg/kg of l-carnitine (p<0.05). hassan et al (12) observed that levels of plasma cholesterol, ldl and hdl decreased significantly by adding l-carnitine in combination with vitamin c in the diet. also, vitamin c significantly increased primary and secondary response of srbc (p<0.05). pardo et al (25) also reported that intake of 1000 ppm vitamin c increased antibody production against srbc in broilers. conclusions: based on the results of the current study, it is concluded that use of 500 mg/kg of vitamin c and 100 mg/kg of l-carnitine in combination can increse performance parameters and improve blood lipid and immune parameters of broilers under heat stress.