328 - Effects of Supplemental Zinc Concentration and Source on Performance and Biomarkers of Immune Status in Receiving Steers

Abstract: Weaned Angus-crossbred steers (n = 72; 626 ± 54 lbs) were enrolled in a 42-d receiving study evaluating trace mineral (TM) source and concentration on growth performance, immune, and TM status. Steers were housed in pens of 6, equipped with GrowSafe bunks to determine individual feed disappearance. Dietary treatments (n = 24 steers/treatment) included: 1) TM from an organic source (Availa4; Zinpro Corp., Eden Prairie, MN) at 7 g∙steer^-1∙d^-1; for 42 d (ORG); 2) ORG for entire 42-d plus AvailaZn to provide 1,000 mg Zn∙steer^-1∙d^-1 for first 14 d (ORG+Z); 3) inorganic TM sources to match TM concentration in ORG (ING) for 42-d. Cattle were weighed on d -1, 0, 14, 41, and 42. Data were analyzed using Proc Mixed with fixed effect of treatment and steer as experimental unit. Initial BW was covariate for growth performance. Final BW and overall ADG did not differ (P ≥ 0.19). However, overall DMI tended to differ (P = 0.06) and G:F was greater (P = 0.04) in ORG+Z than ING, with ORG intermediate. Plasma Zn increased from d 0 to d 14, while d 14 and d 42 did not differ (Day; P = 0.02) and was unaffected by treatment (p value). Based on repeated measures, plasma Cu concentration was greater (P = 0.06) in ING than ORG+Z, while ORG was intermediate and plasma Cu concentrations decreased over time (Day; P = 0.01). Frequency of total circulating NK and CD8 T cells measured on d 0, 14, 42 did not differ (P ≥ 0.07). Markers of activation (CD16, CD44 and CD8) on NK cells measured on d 14 differed by treatment (P ≤ 0.05). In this study, organic TM supplementation improved feed efficiency in received weaned beef steers and TM supplementation influenced markers of immune function.