Several researchers have explored the potential of Cu as a growth-promoting agent in the diets of broiler chicks in excess of the current recommended nutritional level (up to 300 mg/kg of the diet). However, it is not clear whether the reported beneficial or toxic effects of extra Cu last until market age if Cu is supplemented to the diet only during the starter period. Therefore, an experiment was conducted using 1-d-old male broiler chicks to investigate the effects of different levels of Cu [0, 125, and 250 ppm of Cu from cupric sulfate pentahydrate (CuSO4•5H2O)] in excess of the requirement during the starter period (1 to 21 d) on broiler chick performance, bone development, and gastrointestinal development. The addition of 250 ppm of Cu had significant (P < 0.05) negative effects on bird BW, BW gain, and feed intake during the earlier parts of the starter period. However, the addition of 125 ppm of Cu improved (P = 0.05) FCR from 1 to 42 d. Tibia bone ash content and gastrointestinal organ relative weights were not significantly affected (P > 0.05) by additional Cu supplementation; however, the addition of 250 ppm of Cu to the basal diet significantly (P < 0.05) increased liver Cu and decreased blood hematocrit (%) at 20 d. Although feeding 250 ppm of Cu during the starter period had negative consequences on bird performance, moderate levels of Cu (125 ppm) had beneficial effects on FCR without having deleterious effects on bird performance at market age. Caution is advised when considering higher levels of Cu (250 ppm) as a feed supplement in broiler diets
