2. A total of 300 male broiler chicks (Ross 308) were randomly allotted to 5 dietary treatments in a completely randomised design during 1–15 and 15–35 d rearing periods. Experimental treatments consisted of a basal diet with a reduction in Arg content (CON?; starter: 12.1 g/kg and grower: 11.3 g/kg Arg), a CON? diet supplemented with synthetic Arg equal to the required Arg level (CON+; starter: 13.80 g/kg; grower: 12.37 g/kg) and CON? diet supplemented with three levels of GAA (GAA0.6; GAA1.2; and GAA1.8; g/kg).

3. Supplemental GAA at 0.6 and 1.2 g/kg reduced the adverse effects of the CON? diet on weight gain and feed conversion ratio in the starter period, equal to the effect of CON+ diet. During the entire rearing period, such an effect was only seen for broilers fed CON? diet supplemented with 1.2 and 1.8 g/kg GAA (P < 0.05). Proportional weights of liver and abdominal fat were decreased in birds fed diets containing supplemental Arg and 1.8 g/kg GAA compared to the CON? broilers (P < 0.05). Jejunal villus height and villus height to crypt depth ratio were increased in broilers receiving the CON? diet (P < 0.05). Serum concentration of nitric oxide increased when the CON? diet was supplemented with either Arg or 1.8 g/kg GAA (P < 0.05).

4. Dietary inclusion of GAA had an Arg-sparing effect, whereby 1.2 and 1.8 g/kg of supplemental GAA resulted in greater growth performance during the starter and entire rearing periods, respectively. Supplementation with 1.8 g/kg GAA had significant effects on some carcass and physiological parameters.