90 The influence of supplemental zinc, zinc source, and dietary energy level on performance measures of beef steers

Abstract

Abstract The objective was to determine if steer performance improved with supplemental Zn above recommended concentrations with increasing growth rate. Angus steers (n = 72; 324 ± 2.1kg BW) were blocked by BW within growing diets to one of three Zn strategies (ZNTRT) 1) no supplemental Zn (analyzed 36 mg Zn/kg DM; CON), 2) supranutritional Zn as ZnSO4(CON + 120 mg Zn/kg DM; INZN), or 3) supranutritional Zn blend (CON + 60 mg Zn/kg as ZnSO4 + 60 mg Zn/kg as Zn-amino acid complex; ZNBLD) fed for 60 d, then assigned to dietary energy strategies (ENERGY) targeting growth rates of 1.6 (LOW) or 2 kg/d (HI). On d 60, HI steers were transitioned for 7 d and all animals received respective treatments for an additional 91 d finishing period (n = 12). Data were analyzed as a 3×2 factorial in Proc Mixed of SAS with block as fixed effect; steer was experimental unit. After 60 d of dietary treatment BW tended to be greater in Zn-fed steers vs. CON (P = 0.07). Finishing DMI within HI was similar between INZN and ZNBLD, which were greater than CON, while within LOW no differences were detected due to ZNTRT (ZNTRT×ENERGY; P = 0.01). Neither ZNTRT×ENERGY nor ZNTRT effects (P ≥ 0.37) were detected for finishing ADG, HCW, marbling score, yield grade or backfat. However, finishing period ADG, hot carcass weight, marbling score, yield grade, and back fat were greater in HI vs. LOW (P ≤ 0.05). Plasma NEFA concentrations were lesser for steers receiving HI vs. LOW (P = 0.02), while BUN was unaffected by ZNTRT or ENERGY (P ≥ 0.42). Steer performance was influenced by supranutritional Zn and dietary energy.