In all bird species studied, plasma growth hormone (GH) concentrations are high after hatching and during the rapid growth period. Then, plasma GH concentrations decline during the slow growth period to reach low concentrations in adult birds (Harvey et al, 1983). Moravej et al. (2006) indicated that low-energy intake could increase FCR and mean plasma concentrations of GH and T3 but could decrease BW and mean plasma concentrations of T4. They also reported that different protein levels during starter, grower and finisher periods in broilers may change the plasma concentrations of GH, T4 and T3 but keeping protein levels nearly constant during these phases of growth did not change (P<0.05) these hormones.