26 Effect of Steroidal Implants and Zinc Supplementation on Circulating Metabolites and Insulin Sensitivity 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 circulating metabolites and insulin sensitivity in feedlot steers. Steers (n = 6 steers/pen) were stratified by BW in a 3 × 2 factorial design. Dietary treatments were fed for 60 days pre-implant, during this time cattle were transitioned from a roughage-based to a high concentrate diet. 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). Blood was collected from all steers on d 0, 20, 40, and 84 for analysis of serum glucose, insulin, non-esterified fatty acids (NEFA), and urea-N (SUN) in a subset of steers (n = 12 steers/treatment). Glucose, NEFA, and insulin concentrations were used to determine revised quantitative insulin sensitivity check index (RQUICKI) which was calculated as: RQUICKI = 1/[log(Glucose) + log(Insulin) + log(NEFA)]. Data were analyzed as repeated measures in Proc Mixed of SAS. A tendency for a Zn x day effect on serum insulin (Zn × day; P = 0.07) showed no difference between Zn treatments on d 0, 20, or 40 but on d 84 Zn100 was greater than Zn30 while Zn0 was intermediate. An implant × day effect (P = 0.02) for serum insulin was driven by a 45% increase from d 0 to 20 in NO while TE200 cattle did not change in that time. Serum insulin increased with days on feed (P = 0.01). Day 0 serum glucose concentration was greatest in Zn0 and Zn 100; however, on days 40 and 84, Zn100 had greater serum glucose concentration compared with Zn0 while Zn30 was intermediate (Zn × day; P = 0.07). Overall, serum glucose was unchanged over time until a decrease from day 40 to 84 (P = 0.01). A three-way interaction was noted for serum NEFA (Zn × implant × day; P = 0.04) driven by variation in serum NFEA concentration at d 0. Serum urea-N differed by day (P = 0.01) but was otherwise unaffected (P ≥ 0.16). RQUICK1 was greater for TE200 (P = 0.03) cattle on d 40 compared with NO cattle, indicating implanted cattle were more insulin sensitive. RQUICKI index value decreased with days on feed (P = 0.01) indicating lesser insulin sensitivity over time. These data indicate implants influence insulin sensitivity of late-stage finishing cattle and Zn and implants influence circulating metabolites indicative of energetic state.