Effect of different dietary levels of nucleotide supplementation on performance, carcass characteristics, immune system status, small intestine morphology and ileal microbial population of broiler chickens was evaluated using 308 one-day-old mixed-sex Ross 308 broilers in a completely randomized design with 4 treatments and 7 replicates of 11 chicks in each, up to 42 days of age. Experimental treatments included a corn-soybean meal basal diet (control), and the basal diet containing 0.05, 0.1 and 0.2 percent nucleotide supplementation. The results showed that feed intake, body weight gain and feed conversion ratio of the broilers were not significantly affected by experimental treatments. Results of humeral immune system response at 35 days of age showed that the blood serum IgM concentration in 0.2 percent nucleotide group was higher than 0.05 percent group (P< 0.05). Moreover, at this age serum IgG concentration in 0.05 percent nucleotide group was higher than 0.2 percent group (P< 0.05). At 42 days of age, serum IgG concentration in 0.1 percent nucleotide treatment was lower than control group (P< 0.05). The cellular immune system response of chicks fed diet supplemented with 0.1 percent nucleotide at 48 hours after Phytohemagglutinin-P injection was higher than control treatment (P<0.05). On the basis of current experiment results, supplementation of broiler diets with nucleotide improved the cellular immune system response but has no significant effect on other parameters in broiler chickens.

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