165 Interactions Between Steroidal Implants and Zinc Supplementation in Feedlot Steers

Abstract

Abstract Angus-cross steers (n = 144; 362 kg ± 20.4) were used to determine the interaction of Zn and steroidal implants on growth and trace mineral (TM) status. Steers (n = 6/pen) were stratified by BW in a 3 × 2 factorial arrangement. Dietary treatments were fed for 60 days pre-implant, with a roughage-based diet from d -60 to -38, transition to a high concentrate diet, and 23 d on finishing diet before implant. Dietary treatments (8 pens per treatment; Zn as ZnSO4) included: 1) no supplemental Zn (analyzed 54 mg Zn/kg DM; Zn0); 2) 30 mg supplemental Zn/kg DM (Zn30); 3) 100 mg supplemental Zn/kg DM (Zn100). Within Zn treatment, steers received a steroidal implant treatment on d 0: 1) no implant; NO; or 2) high potency combination implant (TE-200, Elanco, Greenfield, IN; 200 mg TBA, 20 mg E2; TE200). Body weights were taken on d -1, 0, 28, 56, and 89, 90. Liver and blood were collected on d 0, 20, 40, and 84 for TM. GrowSafe bunks recorded individual feed intake (steer as experimental unit; n = 24 per treatment). Proc Mixed of SAS evaluated linear and quadratic effects of Zn within implant treatments and the effect of supplemental Zn within TE200. Performance and carcass characteristics used d -60 BW as a covariate. Plasma and liver TM data were analyzed as repeated measures. After 60 d plasma Zn was similar amongst Zn treatments (1.36 mg/L; P = 0.15). TE200 tended to decrease plasma Zn 8.4% from d 0 to 20 whereas NO cattle decreased 3.6% (implant × day; P = 0.08). Supplementation of Zn increased overall liver Zn concentration (P = 0.05). TE200 decreased liver Mn 13.8% from d 0 to 20 while NO decreased 1.2% (implant × day; P = 0.01). During the first 28 d post-implant, no linear or quadratic effects of Zn were noted within NO or TE200 for BW, ADG, G:F, or DMI (P ≥ 0.12). However, within TE200, Zn supplementation improved d 0-28 ADG and G:F (P ≤ 0.04). From d 56-90 steer performance was lackluster; however, within TE200, increasing concentration of supplemental Zn tended to linearly increase G:F (P = 0.07). Within TE200, marbling tended to be quadratically affected (P = 0.06) where Zn30 was lesser than Zn100 with Zn0 intermediate. No additional linear, quadratic, or Zn within TE200 carcass responses (P ≥ 0.11) were noted. From d 0 to 28 Zn supplementation improved ADG and G:F of implanted steers; beyond this, few growth performance differences were noted due to Zn. However, liver and plasma TM results are consistent with our prior work, suggesting steroidal implants increase demand for Zn and Mn following implant administration to support improved growth and efficiency.