L-Arginine supplementation enhances growth performance, lean muscle, and bone density but not fat in broiler chickens.

This study evaluated the effects of crystalline arginine (Arg) on performance and body composition in male broilers. A total of 600 1-day-old Ross 308 broilers were distributed in a completely randomized design, with 5 treatments and 6 replicates of 20 birds. The treatments were given as a percentage of the Ross 308 requirement, and defined as 70, 80, 90, 100 (Ross 308 requirement), and 110% of Arg. Body weight gain (BWG), feed intake (FI), and feed conversion ratio (FCR) were evaluated at 10, 24, and 42 d. Bone growth was measured from 7 to 11 d using mineral apposition rate (MAR) technique. At 42 d, 2 birds per pen were euthanized for bone mineral density (BMD) and body composition measurement using dual-energy X-ray absorptiometry, and liver gene expression and muscle diameter size analysis. The means were subjected to ANOVA and, when significant (P ≤ 0.05), were compared by Dunnett's test. Regression analyses were performed to evaluate trends of Arg dose response. Birds fed 70 and 80% of Arg had lower BWG than the ones fed 100% of Arg (P < 0.001), with quadratic effects for all phases (P < 0.001, R2 = 0.94). The 70% of Arg group showed lower FI compared to 100% from 11 to 24 d and 1 to 42 d (P < 0.009), with quadratic and linear effects (P < 0.049, R2 > 0.72), respectively. The 70% of Arg group showed higher FCR compared to 100% (P < 0.0001) with quadratic effects (P < 0.002, R2 > 0.94) for all periods. At 42 d, the 70% of Arg group showed lower BMD, tissue, and lean muscle percentage than 100% of Arg. There was a quadratic effect of Arg levels on lean muscle (P = 0.046, R2 = 0.89). Therefore, the dietary supplementation with Arg is necessary as it leads to an overall body growth with increased lean deposition and BMD, without increasing fat accretion in Ross 308 broiler chickens.