297 Effects of plasma zinc concentration on longissimus thoracis metabolic status of beef steers

Abstract

Abstract The objective of this study was to examine the role of Zn status on muscle glucose and other metabolites. Angus steers [n = 144; body weight (BW) = 525 ± 30 kg] with varying plasma Zn concentration and implant status served as the initial pool for this secondary experiment. Steers were assigned to one of two implant (IMP) treatments: no implant (NO) or Component TE-200 (TE-200; Elanco, Greenfield, IN) on d 0. Zinc was supplemented as ZnSO4 at 0 mg Zn/kg dry matter (DM; analyzed 54 mg Zn/kg DM), 30 mg Zn/kg DM, or 100 mg Zn/kg DM, starting 60 d before implant day. Steers were fed via GrowSafe bunks (GrowSafe Systems Ltd., Airdie, AB, Canada), and steer was experimental unit. Steers were fed in two blocks with a 14-d stagger for sample logistics. Blood and muscle biopsies of the longissimus thoracis were collected on d 40 after implant, a minimum of 2 h post-feed delivery. Plasma Zn was quantified via ICP-OES and 144 samples were stratified into quantiles by plasma Zn concentration. Samples (n = 12 low and 12 high from NO and TE-200 groups) were identified and designated as low plasma Zn (LOW, 1.1 mg Zn/L average) and high plasma Zn (HI, 1.6 mg Zn/L average) treatments (TRT). Muscle samples from these 48 steers were homogenized and derivatized for subsequent analysis via gas chromatography-mass spectrometry (GCMS) for non-targeted metabolomic analysis. Data were analyzed as a complete randomized design using the MIXED procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC) with fixed effects of TRT, IMP, BLOCK, and TRT×IMP. A TRT×IMP effect was observed for muscle glycine (P = 0.02) where LOW/IMP was similar to HI/NO but had greater glycine concentrations than LOW/NO and HI/IMP. There was a tendency for a TRT×IMP (P = 0.07) effect where LOW/IMP and HI/NO tended to have greater concentrations of hydroxyisovaleric acid. Given the role of glycine in protein synthesis and hydroxyisovaleric acid in leucine metabolism these data suggest differential protein responses to implants in cattle of lesser vs. greater plasma Zn concentrations. Hydroxybutyric acid, a ketone body which can be utilized for energy, tended to be greater in muscle of steers receiving an IMP (P = 0.09). Contrary to our hypothesis that greater plasma Zn would support differential muscle glucose metabolism, no effects of plasma Zn TRT or IMP were noted for glucose, lactate, and other detected metabolites. Both LOW and HI plasma Zn concentrations were still considered adequate, and future research should explore the impact of distinctly deficient and adequate plasma Zn concentration on glucose metabolism pathways in muscle.