Effects of Zinc Source and Level and Added Copper Lysine in the Receiving Diet on Performance by Growing and Finishing Steers11The authors were supported by funds from the New Mexico Agric. Exp. Sta., Las Cruces. Appreciation is expressed to Zinpro Corp., Edina, MN, for partial financial support.

Two hundred eighty-eight newly weaned beef steers were used to evaluate effects of dietary Zn source and level and supplemental Cu Lys on performance and health during receiving and growing and finishing periods. Eight dietary treatments were applied in a 4 x 2 factorial arrangement during the 28-d receiving period (three pens per treatment) and included: Basal, 65% concentrate diet supplemented (DM basis) with 30 mg/kg of Zn (from ZnO) and 3.25 mg/kg ofCu (from CuO); Basal + 5 mg/kg of supplemental Cu from Cu Lys; Low Zn Met, Basal + 35 mg/kg of supplemental Zn from Zn Met; Low Zn Met + 5 mg/kg of supplemental Cu from Cu Lys; High ZnSO4, Basal + 70 mg/kg of supplemental Zn from ZnSO4; High ZnSO4 + 5 mg/kg of supplemental Cu from Cu Lys; High Zn Met, Basal + 70 mg/kg of supplemental Zn from Zn Met; and High ZnMet + 5 mg/kg of supplemental Cu from Cu Lys. At the conclusion of the 28-d receiving period, Cu Lys supplementation was discontinued, and steers remained in their assigned pens, resulting in a total of six pens per each of the four Zn source-level treatments. Over a subsequent 21-d period, steers were stepped up to a 90% concentrate diet, which was fed for a 161-d finishing period. Neither Zn source-level nor Cu Lys supplementation affected performance or morbidity from bovine respiratory disease during the 28-d receiving period. Percentage of morbid steers during both the receiving and step-up periods was decreased (P<.07) by the High ZnSO4 (12.5%) and High Zn Met (9.7%) diets compared with the Basal (22.2%) and Low Zn Met (23.6%) diets. Daily gain and feed efficiency during the 161-d finishing period were not affected by Zn source-level, but DMI was greater (P<.10) by steers fed the Low Zn Met, High ZnSO4, and High Zn Met diets than by those fed the Basal diet. Supplemental Cu Lys fed during the receiving period had a negative effect on daily gain (P<.02) and DMI (P<.09) during the subsequent growing and finishing period. Carcass measurements were not affected by Zn source-level. These results suggest no advantages in daily gain and feed efficiency as a result of supplying Zn in excess of requirements; however, higher levels of Zn seemed to have beneficial effects on the health of newly weaned beef steers.