Linear regression of ADG, FCR to intake level of Av-Cu. A, linear regression of ADG (g) to intake level of Av-Cu (mg/ kg) in phase 2; B, linear regression of FCR to intake level of Av-Cu (mg/ kg) in phase 2; C, linear regression of ADG (g) to intake level of Av-Cu (mg/ kg) in whole experimental period; D, linear regression of FCR to intake level of Av-Cu (mg/ kg) in whole experimental period.