A 8-wk feeding experiment was conducted to investigate the effect of dietary supplementation with Arg on growth performance, nutrient digestibility, metabolizable energy, and intestinal morphology of growing turkeys. A total of one hundred and eighty 56-d-old male grower turkeys were weighed individually and randomly assigned to 1 of 3 dietary treatments with 6 replicate pens and 10 turkeys per pen in a completely randomized design. Dietary treatments consisted of basal diets supplemented with 0, 0.5, and 1.0 g Arg/kg. Growth response was measured during the grower (d 56–84) and finisher (d 84–112) phases, while nutrient digestibility, metabolizable energy, and intestinal morphology were measured at d 84 and 112. Arginine supplementation had no effect on growth response during the grower phase. During the finisher phase, feed conversion ratio decreased initially as Arg supplementation increased from 0 to 0.5 g/kg, but it increased with the 1.0 g Arg/kg (quadratic, P=0.028). At d 84, grower turkeys fed diets supplemented with 1.0 g Arg/kg had greater (linear, P
