عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Three hundred eighteen young Holstein bulls (initial BW = 375 ± 17.5 kg) were randomly allotted to one of six treatments in a completely randomized design for 56 d the treatments of which consisted of 1) the basal diet (control); 2) basal diet plus 30 mg of Cu/kg of DM as CuSO4; 3) basal diet plus 150 mg of Zn/kg of DM as ZnSO4; 4) basal diet plus chlortetracycline (200 mg/animal/d; CTC); 5) basal diet + Cu + CTC; and 6) basal diet + Zn + CTC within the same dose. Effects of treatments on blood metabolites and Back fat thickness, Rump fat thickness, Longissimus muscle area and Hip height were evaluated. Serum urea nitrogen (P < 0.001) and plasma total protein (P < 0.001) were different among treatments. Copper supplementation improved ultrasound index, however, zinc supplementation negatively affected (P < 0.001). As a result, the control of Cu and Zn levels, as replacers for CTC, in the diet of young bulls can increase Longissimus muscle area and can decrease fat thickness.