Marginal deficiencies of dietary arginine and methionine could suppress growth performance and immunological responses in broiler chickens.

The present study was conducted to investigate the effects of different levels of dietary arginine (Arg) and methionine (Met) on performance, immune responses, and carcass characteristics of broiler chickens. A total of 540 day-old Ross 308 broiler chicks were randomly assigned into the nine experimental diets, consisting five replicates of 12 birds each. Dietary treatments included three different levels (90%, 100%, and 110% of National Research Council [NRC] specifications) of either dietary Arg or Met, which were fed to the birds according to a 3 × 3 factorial arrangement of treatments during a 42 days feeding trial. Results showed that supplementation of Arg and Met into the deficient-diets increased (p < .01) weight gains during all trial periods. Although average daily feed intake (ADFI) was not influenced by dietary treatments, increasing Arg up to 100% of NRC recommendations improved (p < .05) feed conversion ratio (FCR) throughout the trial period. Similarly, supplementation of deficient-diets with Met improved FCR values. There was a significant (p < .01) Arg × Met interaction for ADFI during the starter period; increasing the dietary Arg level increased ADFI when the diets were deficient in Met, while had an opposite effect in diets containing higher dietary Met levels. On the other hand, dietary Met fortification improved (p = .067) FCR values to a greater extent in 110% Arg-diets during the entire trial period. Although different levels of Arg and Met had no marked effects on carcass yield and abdominal fat percentage, supplemental Arg up to 100% of NRC values increased (p < .01) the relative weights of spleen and bursa of Fabricius. Furthermore, bursa weight was affected by Arg × Met interaction (p < .01), so that supplemental Arg level of 100% of NRC increased the relative bursa weight in birds that were fed diets containing 90% and 110% of Met. Serum uric acid level was decreased (p < .05) as a result of dietary Arg fortification up to 110% of NRC recommended values. Supplementation of deficient-diets with Met decreased (p < .05) serum cholesterol level. Although Newcastle antibody titer was not affected by dietary Arg or Met levels, Arg fortification of deficient-diets increased (p < .001) antibody responses against infectious bronchitis (IBV) and bursal (IBD) disease viruses. Similarly, Met supplementation of deficient-diets increased IBD antibody titer. There were significant (p < .05) Arg × Met interactions for IBV and IBD titers; Met fortification of 110% Arg-diets was more effective in increasing antibody titers. An increase in dietary Met level up to 100% of NRC values increased (p < .001) serum concentration of γ-globulins. The present findings imply that supplemental Arg could affect feed efficiency and antibody responses when the diets were already fortified with a sufficient Met level.