Effects of feeding ractopamine hydrochloride in combination with zinc or chromium on growth performance, carcass characteristics, and meat quality of finishing steers

Chromium;Ractopamine Hydrochloride;Steers;Zinc

Edenburn, Bailey Marie ; Felix ; Tara

关键词: Chromium;    Ractopamine Hydrochloride;    Steers;    Zinc;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/88944/EDENBURN-THESIS-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Cattle growth rate, feed efficiency, and carcass quality directly influence profitability of beef cattle producers throughout the United States. Volatile feed costs have made it economical for livestock producers to use technologies to improve efficiency and profitability. Beta adrenergic agonists are one such technology and are a class of feed additives that have been widely fed by the feedlot industry in the last decade. One product available on the market is ractopamine hydrochloride (RAC), a beta-agonist that acts as a nutrient repartitioning agent to shift nutrient deposition from fat to lean tissue. There are other additives which may work in combination with RAC to enhance lean tissue deposition and improve meat quality. Of particular interest in this thesis are trace minerals, specifically zinc (Zn) and chromium (Cr) fed in combination with RAC. Zinc is not only involved in protein synthesis through its integral role in all 3 RNA polymerases (Cousins, 1998), but Harris et al. (2012) reported Zn in combination with RAC reduced β-receptor desensitization in bovine muscle satellite cells. This suggests that Zn supplementation may prolong the response of skeletal muscle to RAC. In addition to Zn, Cr is integral to glucose metabolism and has been shown to increase glucose clearance rates following glucose infusion (Sumner et al., 2007). We hypothesized that feeding RAC in combination with Zn would increase efficiency of gain and muscle growth over feeding RAC alone, that RAC in combination with Cr would increase intramuscular fat deposition over RAC alone, and RAC in combination with Zn and Cr would enhance both lean tissue accretion and marbling. Therefore, objectives were to determine the effects of feeding RAC with Zn and Cr on feedlot growth performance, carcass characteristics, and meat quality. Crossbred steers (N = 179; average initial BW = 533 ± 94 kg) were blocked by BW and allotted to 30 pens, 10 pens per block, for a 63 d trial. Pens were randomly assigned to 1 of 5 treatments: (1) control (CONT), (2) RAC only (RO), (3) RAC + Zn (RZ), (4) RAC + Cr (RC), or (5) RAC + Zn + Cr (RZC). Steers were fed the same basal diet containing 60% dry rolled corn, 20% corn silage, 10% DDGS, and 10% supplement. Trace minerals were fed from d 0 to 63 and to target 1 g of Zn/steer·d-1 (KemTRACE Zn; Kemin Industries, Inc., Des Moines, IA) and 3 mg Cr/steer·d-1 (KemTRACE Cr; Kemin Industries, Inc.) for Zn and Cr treatments, respectively. Dry rolled corn, 0.605 kg/steer, was removed from the ration and 400 mg RAC, per 0.605 kg of ground corn carrier, was top dressed per steer immediately following feed delivery to pens fed RAC. Data were analyzed using the MIXED procedure in SAS. There were no effects (P > 0.45) of trace mineral supplementation during the first 35 d of the trial, prior to RAC supplementation, on DMI, ADG, or G:F. There were also no effects (P > 0.46) of treatment for the entire 63 d of the trial on DMI, ADG, or G:F. Despite the lack of differences in live performance, steers fed RO and RC averaged 0.10 kg/d greater (P = 0.10) carcass ADG than steers fed RZC and CONT, while steers fed RZ were intermediate and not different. Steers fed RO had 13% greater (P = 0.09) carcass G:F than steers fed CONT. Steers fed RO and RC averaged 5.5 kg heavier (P = 0.09) HCW than steers fed RZC and CONT, while steers fed RZ were intermediate and not different. There were no treatment effects (P > 0.32) on LM area, 12th rib fat, marbling score, KPH, carcass yield, or USDA yield grade and distribution. However, carcasses from steers fed RC had the greatest (P = 0.10) percentage grading USDA Select. There were no treatment effects (P > 0.20) on shear force, intramuscular fat, pH, a*, and b*. Steaks from steers fed RO and RC had 11.4% greater (P = 0.08) cook loss than steaks from steers fed CONT and RZC, whereas steaks from steers fed RZ were intermediate and not different. Also, steaks from steers fed RC had 2.11 units greater (P = 0.03) L* values than steaks from steers fed RZ, steaks from steers fed CONT, RO, and RZC were intermediate. In feedlot steers, addition of either Cr and Zn, alone or in combination did not improve growth performance or meat quality when fed in combination with 28 d of RAC supplementation; however, RAC, fed alone or in combination with Cr, did increase HCW.