Influence of level and form of supplemental zinc on feedlot growth performance and carcass characteristics of calf-fed Holstein steers

The objectives of this study were to evaluate the influence of level and source of supplemental Zn on growth performance and dietary energetics in calf-fed Holstein steers. A total of 168 steers (BW = 133 ± 7 kg) were used in a 336-d study. Treatments consisted of diets based on steam-flaked corn supplemented with (DM basis) (1) 20 mg of Zn/kg of DM as ZnSO4; (2) 10 mg of Zn/kg of DM as ZnSO4 plus 10 mg of Zn/kg of DM as Zn betaine; (3) 20 mg of Zn/kg of DM as Zn betaine; or (4) 40 mg of Zn/kg of DM as ZnSO4. Overall (d 1 to 336) there were no treatment effects (P > 0.10) on carcass-adjusted ADG, gain efficiency, and estimated dietary NE. At the 20 mg/kg level of Zn supplementation, the proportion of supplemental Zn provided as chelate did not influence overall ADG, gain efficiency, or dietary NE (P > 0.10). The proportion of Zn supplemented as chelate did not affect (P > 0.10) carcass weight, KPH, LM area, or marbling score. However, DP was greater (quadratic effect, P = 0.01) for steers receiving the 50:50 blend of ZnSO4 and Zn betaine. Carcass yield grade improved (linear component, P = 0.03) with proportion of supplemental Zn as chelate. We conclude that at a 20 mg/kg (DM basis) level of supplementation, Zn source does not affect growth performance of calf-fed Holstein steers. Increasing level of Zn supplementation (as ZnSO4) from 20 to 40 mg/kg will not further enhance overall performance responses.