Feeding zilpaterol hydrochloride (ZH) with ruminally protected AA was evaluated in a small-pen feeding trial. Crossbred steers ( = 180; initial BW = 366 kg) were blocked by weight and then randomly assigned to treatments (45 pens; 9 pens/treatment). Treatment groups consisted of no ZH and no AA (Cont-), ZH and no AA (Cont+), ZH and a ruminally protected lysine supplement (Lys), ZH and a ruminally protected methionine supplement (Met), and ZH and ruminally protected lysine and methionine (Lys+Met). Zilpaterol hydrochloride (8.3 mg/kg DM) was fed for the last 20 d of the finishing period with a 3-d withdrawal period. Lysine and Met were top dressed daily for the 134-d feeding trial to provide 12 or 4 g·hd·d, respectively, to the small intestine. Carcass characteristics, striploins, and prerigor muscle samples were collected following harvest at a commercial facility. Steaks from each steer were aged for 7, 14, 21, and 28 d, and Warner-Bratzler shear force (WBSF) was determined as an indicator of tenderness. Prerigor muscle samples were used for immunohistological analysis. Cattle treated with Met and Lys+Met had increased final BW ( < 0.3) and ADG ( < 0.05) compared to Cont- and Cont+. Supplementation of Lys, Met, and Lys+Met improved G:F ( < 0.05) compared to Cont- during the ZH feeding period (d 111 to 134) as well as the entire feeding period ( < 0.05). Zilpaterol hydrochloride increased carcass ADG ( < 0.05) when compared to non-ZH-fed steers. Methionine and Lys+Met treatments had heavier HCW ( < 0.02) than that of Cont-. Yield grade was decreased ( < 0.04) for Cont+ steers compared to steers treated with Lys, Lys+Met, and Cont-. Tenderness was reduced ( < 0.05) with ZH regardless of AA supplementation. Lysine, Met, Lys+Met, and Cont+ had less tender steaks ( < 0.05) throughout all aging groups compared to Cont-. Steaks from Lys-treated steers were less tender ( < 0.05) than those of Cont+ during the 7- and 14-d aging periods. Nuclei density was the greatest with Cont- cattle compared to all other treatments suggesting a dilution effect of the nuclei in the larger muscle fibers with ZH feeding. Supplementation of Met in conjunction with ZH feeding increased ADG and HCW although this may lead to decreased tenderness even after aging for 28 d. These findings indicated that steers fed ZH may require additional AA absorbed from the small intestine to maximize performance.

Providing cattle a more bioavailable zinc (Zn) source prior to administering a beta adrenergic agonist (βAA) may enhance the metabolic pool of primary nutrients that will influence the magnitude of the βAA response. Calf-fed Holstein steers were supplemented with a Zn methionine supplement (ZnMet; ZINPRO®; Zinpro Corporation, Eden Prairie, MN) for 115 ± 5 days prior to harvest along with zilpaterol hydrochloride (ZH; Zilmax®; Merck Animal Health, Summit, NJ) for the last 20 days with a 3-day withdrawal to evaluate the effects on growth and carcass performance together with gene and protein expression of skeletal muscle, adipose tissue, and fatty acid composition of polar and neutral lipid depots. Steers (n = 1296; initial weight = 468.5 ± 0.5 kg) were sorted by weight, blocked by harvest date, and randomly assigned to pens (n = 12) and treatments: control (90 ppm Zn from ZnSO4) and ZnMet (Control plus 720 mg Zn from ZnMet/hd/d). There were no differences (P > 0.05) in growth performance or carcass characteristics. The ZnMet-fed cattle had reduced (P < 0.05) abundance of myosin heavy chain (MHC)-IIX, β1-adrenergic receptor (βAR), peroxisome proliferator-activated receptor gamma, and stearoyl-CoA desaturase mRNA in skeletal muscle tissue. The ZnMet cattle had greater (P < 0.05) abundance of MHC-II protein, increased MHC-IIA and IIX cross-sectional areas (P < 0.05), an increased percentage of MHC-I fibers (P < 0.05), and a decreased percentage of MHC-IIX fibers (P < 0.05). The combination of ZnMet and ZH had positive biological effects on musculoskeletal tissue; however, these molecular effects were not significant enough to impact overall feedlot and carcass performance.

Effects of a tannic acid blend (ByPro; Silvateam USA, Ontario, CA) added to steam-flaked corn-based fishing diets on beef cattle growth performance, carcass characteristics, nutrient digestibility, fecal N volatilization, and meat lipid oxidation were evaluated. Steers ( = 144; 349 ± 25 kg initial BW) were blocked by initial BW and assigned randomly to 1 of 3 treatments with 12 pens/treatment and 4 steers/pen and fed ad libitum. Treatments included a control (CON; no ByPro) and ByPro fed at 30 or 60 g DM/steer daily (30-ByPro and 60-ByPro, respectively). Pen fecal samples were collected 7 d after cattle were shipped to slaughter for estimation of N volatilization. Strip loins were aged for 21 d for evaluation of color and antioxidant activity. Intake quadratically increased ( = 0.05) from d 0 to 35, whereas linear trends were observed for increased DMI from d 0 to 105 and d 0 to slaughter ( = 0.07 and = 0.06, respectively), resulting in a 3.7% greater overall DMI for 60-ByPro than for CON. No differences were detected for carcass-adjusted ADG ( = 0.65) or G:F ( = 0.17). Carcass characteristics including HCW ( = 0.52), fat thickness ( = 0.32), LM area ( = 0.57), quality grade ( = 0.44), yield grade ( = 0.29), and percentage of condemned livers ( = 0.13) were not affected by treatments. Apparent total tract digestibility of starch linearly decreased tendency ( = 0.03) with increasing ByPro dose, whereas tends for a linear decrease ( = 0.09) in CP and a quadratic increase ( = 0.09) in OM digestibility were observed. No effects of treatment ( ≥ 0.39) were noted for fecal N volatilization. An increase ( < 0.01) in metmyoglobin in strip loin steaks was observed with ByPro inclusion. Oxymyoglobin decreased ( < 0.01) as display day progressed, except on d 5, at which time CON and 30-ByPro steaks had lower proportions than 60-ByPro steaks. Only subtle changes in discoloration ratio and deoxymyoglobin were observed, whereas no effects ( ≥ 0.43) for pH or thiobarbituric acid reactive substances were noted. Feeding ByPro increased DMI during the first half of the feeding period without negatively affecting gain efficiency; however, fecal N retention was not altered by ByPro. ByPro did not negatively affect meat quality or carcass characteristics, and it did not seem to affect retail meat antioxidant activity.

Abstract A randomized complete block design experiment with 32 yearling crossbred steers (average BW = 442 ± 17.0 kg) fed a steam-flaked corn-based diet was used to evaluate the effects of dietary Zn (KemTRACE® Zinc Propionate 27; Kemin Industries, Inc., Des Moines, IA) supplementation on live growth performance, skeletal muscle fiber, and beta-adrenergic receptor (β-AR) characteristics during the finishing phase. Steers were blocked by BW (n = 4 blocks; 8 steers/block), assigned to pens (n = 4 steers/pen), and randomly assigned to the following treatments: control (CON; 0.0 g/ (hd · d) of additional Zn) or additional dietary Zn (ZnP; 1.0 g/(hd · d) additional Zn). The basal diet contained Zn (60 ppm DM basis) from ZnSO4; additional Zn was top-dressed at feeding. Ractopamine hydrochloride (RH; Optaflexx®: Elanco Animal Health, Greenfield, IN) was included at 300 mg/ (hd · d) for the final 28 d of the 111-d feeding period. Longissimus muscle biopsy samples, BW, and blood were obtained on d 0, 42, 79, and 107. Final BW was collected prior to shipping on d 111. Biopsy samples were used for immunohistochemical (IHC), mRNA, and protein analysis. Serum urea- N (SUN) and NEFA concentrations were measured. Steers fed ZnP had greater ADG (P = 0.02) and G:F (P = 0.03) during the RH feeding period compared to CON. There were no differences (P &gt; 0.05) in other growth performance variables, carcass traits, mRNA abundance, or relative protein concentration for fiber type and β-AR. Fiber type I and IIA had no differences for cross-sectional area; however, IIX area was greater for CON (P &lt; 0.04) compared to ZnP, and increased (P &lt; 0.02) over time. There were no differences between treatments for β1-adrenergic receptor density (β1-AR; P &gt; 0.05) in skeletal muscle tissue throughout the study. A treatment × day interaction was observed in β2-adrenergic receptor density (β2-AR; P = 0.02) and β3-adrenergic receptor density (β3-AR; P = 0.02) during the RH feeding period, where the abundance of the receptors increased with ZnP but did not change in CON. Compared to CON, ZnP had greater (P &lt; 0.01) mean NEFA concentrations. Mean SUN concentrations did increase by day (P &lt; 0.01). Additional dietary Zn, supplied as Zn propionate, upregulates β2-AR and β3-AR, and improves growth performance in feedlot steers during the RH feeding period, likely through a shift of resource utilization from lipogenesis to muscle maintenance and hypertrophy.

The objective of this study was to evaluate the effects of increasing concentrations of Cr propionate (CrP) on feedlot performance, blood parameters, carcass characteristics, and skeletal muscle fiber properties in feedlot steers. Crossbred steers (n=32; 367±2.5 kg; 16 pens; 2 hd/pen) were blocked by BW, and treatment was randomly assigned to pen: 1) 0 mg added Cr/kg diet DM (control), 2) 0.15 mg added Cr/kg diet DM (Cr propionate (CrP); KemTRACE® Chromium 0.04%, Kemin Industries, Des Moines, IA), 3) 0.30 mg added Cr/kg diet DM, and 4) 0.45 mg added Cr/kg diet DM. Steers were fed ad libitum, and the treatment was top-dressed at the time of feeding. Body weights, blood samples, and longissimus biopsies were collected before feeding on d 0, 28, 56, 91, 119, and 147. Blood sera were harvested for analysis of glucose, insulin, sera urea nitrogen (SUN), and NEFA concentrations. Longissimus biopsies were collected for gene expression, protein expression, and immunohistochemical (IHC) analysis. Pen was the experimental unit for live and carcass data, and steer was the experimental unit with day as a repeated measure for sera and IHC analyses. For the entire duration of the trial, a linear increase in ADG (P=0.01) and improvement in G:F was observed (P=0.01) with no change in DMI (P=0.11) with increasing CrP. A linear increase in HCW (P≤0.01) with no other changes in carcass composition were noted (P≥0.38) as the level of dietary CrP increased. There was no effect of treatment on any sera parameters measured (P≥0.10). No difference was detected for gene or protein expression of GLUT4 due to CrP supplementation (P≥0.10). For skeletal muscle fiber distribution and cross-sectional area, there was no effect of treatment (P≥0.10). Density of total GLUT4 did not change due to CrP (P≥0.10). Internalization of GLUT4 was increased in the 0.30 mg/kg and 0.45 mg/kg treatments (P&lt;0.01). For total nuclei density and myonuclei density, there were treatment × day interaction tendencies (P≤0.08). Supplementation of CrP did not alter density of satellite cells (P≥0.10). The number of transporters located in the sarcolemma of skeletal muscle fibers did decrease, implying fewer proteins were needed to transport extracellular glucose into the muscle fiber. Therefore, CrP may augment cellular function and growth via increased efficiency of GLUT4 function. These results indicated CrP increases BW, ADG, and HCW, without changes in circulating sera parameters or total GLUT4 expression.